Rehabilitation of unilateral profound sensorineural ...
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Rehabilitation of unilateral profound sensorineural hearing loss with a bone anchored hearing aid Katrise Mary Eager Bachelor of Speech Pathology, University of Queensland, 1996 Postgraduate Diploma of Audiology, University of Queensland, 1997 This thesis is presented for the degree of Masters of Medical Science - Research The University of Western Australia School of Surgery 2009
Transcript of Rehabilitation of unilateral profound sensorineural ...
Rehabilitation of unilateral profound sensorineural hearing loss with a bone anchored hearing aid
Katrise Mary Eager
Bachelor of Speech Pathology, University of Queensland, 1996
Postgraduate Diploma of Audiology, University of Queensland, 1997
This thesis is presented for the degree
of
Masters of Medical Science - Research
The University of Western Australia
School of Surgery
2009
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ABSTRACT
The long-term outcomes of subjects fitted with a bone anchored hearing aid
(BAHA) for a unilateral profound sensorineural hearing loss (UPSHL) are still
evolving. Previous studies have focused on the comparison between short-
term outcomes obtained with hard-wired contralateral routing of signal (CROS)
hearing aids and those obtained with BAHA devices. Published results on
subjects who have worn their BAHA devices for UPSHL for more than twelve
months are limited.
This study explored the long-term outcomes of adults fitted with a BAHA for
UPSHL. The aims were firstly to examine subjects’ pre-operative and post-
operative speech perception in quiet and noise, as well as administer two
standardised questionnaires, the Abbreviated Profile of Hearing Benefit
(APHAB) and the Glasgow Hearing Aid Benefit Profile (GHABP). The second
aim was to evaluate the responses of implanted subjects following the pre-
operative test protocols using a supplementary questionnaire, the Single Sided
Deafness Questionnaire (SSDQ). The third aim was to monitor the subjects’
implant or repair issues. In addition, questionnaire results were compared to
subjects who underwent pre-operative assessment but were not implanted.
All subjects had a UPSHL resulting from various aetiologies including vestibular
schwannoma or other skull base tumour removal, viral infections, cochlear
trauma, idiopathic sudden hearing loss, and Meniere’s disease. There was a
significant difference between the implanted groups’ pre- and post-operative
outcomes measures, indicating a treatment effect from the fitting of the BAHA
device. No significant changes were found with the non-implanted groups’ long-
term outcome measures in regards to their perceived hearing difficulties. No
significant correlations were found between outcome measures and gender,
age of fitting, length of deafness, or ear affected for either group.
The implanted subjects’ responses on the SSDQ revealed depreciation over
time in overall usage and satisfaction rates. However, these rates remained
high when compared to other reported studies. The overall outcome results
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revealed that the BAHA remains one of the treatment methods of choice for
hearing rehabilitation with this subject group. Further studies comparing the
BAHA to wireless frequency modulated (FM) contralateral routing of signal
(CROS) systems, as well as the fitting of FM systems compatible with the BAHA
to this subject group of UPSHL are warranted to ascertain respective
advantages of these different treatment options.
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TABLE OF CONTENTS Abstract ............................................................................................................. ii
Table of Contents ............................................................................................. iv
Acknowlegements ........................................................................................... ix
List of Figures ................................................................................................. xii
List of Tables .................................................................................................. xiv
Abbreviations .................................................................................................. xv
Glossary ....................................................................................................... xviii
Chapter 1: Introduction .................................................................................... 1
1.1 Unilateral profound sensorineural hearing loss (UPSHL) .............................. 3
1.1.1 Types of hearing loss ................................................................ 4
1.1.2 Audiological test battery ............................................................ 6
1.2 Incidence of UPSHL ................................................................................. 13
1.2.1 Incidence of congenital UPSHL .............................................. 14
1.2.2 Incidence of acquired UPSHL ................................................. 14
1.3 Congenital causes of UPSHL ................................................................... 15
1.4 Acquired UPSHL ...................................................................................... 16
1.4.1 Trauma ................................................................................... 16
1.4.2 Metabolic ................................................................................ 17
1.4.3 Neoplasms .............................................................................. 17
1.4.4 Infections ................................................................................ 19
1.4.5 Ototoxicity ............................................................................... 19
1.4.6 Immunological ......................................................................... 20
1.4.7 Idiopathic ................................................................................ 20
1.5 Loss of binaural hearing cues ................................................................... 21
1.5.1 Head shadow effect ................................................................ 23
1.5.2 Binaural summation ................................................................ 24
1.5.3 Binaural squelch ..................................................................... 25
1.5.4 Binaural redundancy ............................................................... 25
1.5.5 Localising sound ..................................................................... 26
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1.6 Studies on unilateral hearing loss ............................................................. 27
1.7 Quality of life aspects and outcome measures ......................................... 29
1.7.1 Abbreviated Profile of Hearing Aid Benefit (APHAB) .............. 32
1.7.2 Glasgow Hearing Aid Benefit Profile (GHABP) ....................... 33
1.7.3 Single Sided Deafness Questionnaire (SSDQ) ....................... 34
1.8 Summary .................................................................................................. 35
Chapter 2: Traditional options for UPSHL .................................................... 37
2.1 Transcranial hearing aids ......................................................................... 37
2.2 Contralateral routing of signal (CROS) hearing aids ................................ 38
2.3 Frequency modulated (FM) systems ........................................................ 42
2.4 Monitoring hearing loss ............................................................................ 43
Chapter 3: The bone anchored hearing aid (BAHA) .................................... 46
3.1 Background information on the BAHA ...................................................... 46
3.1.1 Surgical procedure .................................................................. 46
3.1.2 Direct bone conduction ........................................................... 50
3.1.3 BAHA sound processors ......................................................... 52
3.1.4 Post surgical complications and management ........................ 58
3.2 Use of BAHA in hearing rehabilitation ...................................................... 61
3.3 Application of BAHA with UPSHL ............................................................. 63
3.3.1 How the BAHA works with UPSHL ......................................... 65
3.3.2 Background studies ................................................................ 65
3.3.3 Recent studies ........................................................................ 69
Chapter 4: Purpose of the study .................................................................... 72
Chapter 5: Material and methods .................................................................. 74
5.1 Subject selection ...................................................................................... 74
5.1.1 Subject inclusion criteria ......................................................... 74
5.1.2 Subject recruitment ................................................................. 76
5.1.3 Study ethical approval ............................................................. 76
5.2 Test equipment ......................................................................................... 77
5.2.1 General test equipment ........................................................... 77
5.2.2 BAHA test equipment .............................................................. 78
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5.2.3 BAHA setting protocols ........................................................... 78
5.3 Test protocols ........................................................................................... 79
5.3.1 Pure tone audiometry testing .................................................. 80
5.3.2 Immittance audiometry testing ................................................ 80
5.3.3 Speech audiometry under headphones .................................. 81
5.3.4 Free-field speech testing set up .............................................. 81
5.5.5 Free-field speech testing ......................................................... 82
5.3.6 Single word testing in quiet ..................................................... 83
5.3.7 Sentence testing in noise ........................................................ 84
5.3.8 Protocols for implanting subjects and post-surgical fitting of
sound processor .................................................................................... 85
5.3.9 Questionnaire administration .................................................. 86
5.3.10 Data analysis ......................................................................... 87
Chapter 6: Results .......................................................................................... 88
6.1 Subjects .................................................................................................... 88
6.1.1 General subject characteristics ............................................... 89
6.1.2 Implanted subject characteristics ............................................ 90
6.1.3 Non-implanted subject characteristics .................................... 92
6.1.4 Subject implantation and BAHA device ................................... 95
6.2 Speech testing in quiet via free-field testing ............................................. 97
6.2.1 Pre-operative speech results of Group A ................................ 97
6.2.2 Pre-operative speech results of Group B/C ............................ 98
6.2.3 Post-operative results of Group A ........................................... 99
6.2.4 Post-operative results of Group B/C ..................................... 101
6.3 Speech testing in noise .......................................................................... 101
6.3.1 Pre-operative results of Group A ........................................... 101
6.3.2 Pre-operative results of Group B/C ....................................... 102
6.3.3 Post-operative results of Group A ......................................... 103
6.3.4 Post-operative results of Group B/C ..................................... 104
6.4 Abutment and repair issues .................................................................... 105
6.5 Questionnaires ....................................................................................... 109
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6.5.1 Implanted subjects APHAB results ....................................... 109
6.5.2 Non-implanted subjects – APHAB results from initial and
repeated surveys ................................................................................. 110
6.5.3 Implanted subject GHABP results ......................................... 111
6.5.4 Non-implanted subjects – GHABP results from initial and
repeated surveys ................................................................................. 112
6.5.5 Alternative aids and employment .......................................... 113
6.5.6 SSDQ .................................................................................... 113
Chapter 7: Discussion .................................................................................. 117
7.1 Subjects .................................................................................................. 117
7.1.1 Subject selection ................................................................... 117
7.1.2 Hearing loss group classification ........................................... 119
7.1.3 Implantation uptake of the subject group .............................. 119
7.1 4 Implanted subject numbers ................................................... 122
7.2 Speech testing ........................................................................................ 123
7.2.1 Speech testing in quiet .......................................................... 124
7.3 Speech-in-noise testing .......................................................................... 127
7.3.1 Testing in S0:N0 condition .................................................... 135
7.3.2 Testing in S0:N90/S0:N270 conditions ................................. 136
7.4 Abutment and device issues ................................................................... 138
7.4.1 Post-operative skin infections and complications .................. 138
7.4.2 Repair issues ........................................................................ 139
7.4.3 Abutment removal and discontinued usage of BAHA ........... 141
7.5 Questionnaires ....................................................................................... 143
7.5.1 APHAB .................................................................................. 143
7.5.2 GHABP .................................................................................. 145
7.5.3 SSDQ .................................................................................... 147
7.5.4 BAHA outcome measures with non-implanted subjects ........ 151
7.6 Limitations to the study ........................................................................... 152
7.7 Future studies ......................................................................................... 153
Chapter 8: Conclusions ................................................................................ 156
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Chapter 9: References .................................................................................. 159
Chapter 10: Appendices ............................................................................... 179
Appendix I ....................................................................................................... 180
Appendix II ...................................................................................................... 181
Appendix III ..................................................................................................... 183
Appendix IV..................................................................................................... 184
Appendix V ..................................................................................................... 187
Appendix VI .................................................................................................... 190
Appendix VII.................................................................................................... 193
Appendix VIII................................................................................................... 195
Appendix IX..................................................................................................... 197
Appendix X ..................................................................................................... 198
Appendix XI .................................................................................................... 199
Appendix XII.................................................................................................... 200
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ACKNOWLEDGEMENTS
I am grateful to the following people and organisations who have helped me
over the last four and half years in order to produce this Masters thesis.
I would like to thank my supervisors, Associate Adjunct Professor, Dr Robert
Eikelboom and Professor Marcus Atlas, for all their help and guidance with this
project. They have supported me both professionally and personally since the
inception of this thesis, which has been greatly appreciated. Additionally, Dr
Eikelboom, kindly did all the statistical analysis for this study. I would also like
to thank Associate Adjunct Professor, Paul Davis, who gave audiological advice
about the study and its content.
The study was funded by the Ear Sciences Institute Australia (ESIA), Nedlands,
Western Australia. I wish to thank the Institute for its continued interest and
financial support, and to Gemma Upson who has supported the study through
access to the clinical services at the Lions Hearing Clinic-Implant Centre at
Nedlands, Western Australia.
Thank you to Entific Medical System’s distributor, Shine Medical, for the loan of
test equipment during the initial years of the study. Jodie Oakley and Chris
Broadbent at Cochlear Limited, Australia kindly allowed the use of equipment
for testing procedures, loan devices and provided technical advice regarding
aspects of the bone anchored hearing aid.
I would like to thank the audiologists, Roberta Marino and Gemma Ivey at Lions
Hearing Centre-Implant Centre, Nedlands, Western Australia, as well as Celene
McNeill, Erica Caiuby and Monique Mainey from the Healthy Hearing & Balance
Care, Bondi Junction, New South Wales for subject data collection that was
used in this study, but most importantly for giving me great support and
providing important feedback during the whole process.
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The technical support and equipment design involved student and staff at Lions
Ear & Hearing Institute (LEHI), later ESIA. Mark Gallop, research officer, for the
development of the on-line data collection website. The University of Western
Australia, Engineering students who did vacation work on this project, Jennifer
Hubble and Gabrielle van der Linde, and University of Western Australia,
Nedlands, WA.
I would like to thank the subjects recruited from the clinical caseloads of the
Lions Hearing Clinic-Implant Centre and Healthy Hearing & Balance Care, who
gave generously of their time to allow this study to be completed.
Cathy Sucher and Gae Di Francesco who tirelessly read drafts of my thesis,
and provided sound audiological advice and editing skills.
A big thanks to my sister, Zoë Pozza who helped edit the final draft.
Finally, and most importantly, I want to thank my husband, Alan and my sons,
Patrick and Angus for being understanding and patient when I was not able to
fulfil my responsibilities as a wife and mother when working on this study.
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STATEMENT OF CANDIDATE CONTRIBUTION
This is to certify that:
i. The thesis consists of only my original work towards the Masters of
Medical Science-Research.
ii. Due acknowledgement has been made in the text to all other material
used.
iii. This thesis is under 50,000 words in length, exclusive of footnotes,
tables and appendices.
Signature: ……..…………………………………….…………………………….
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LIST OF FIGURES
Figure 1.1. Audiogram of a left UPSHL ............................................................. 4
Figure 1.2. The anatomical components of the ear ........................................... 5
Figure 1.3. Degrees of hearing loss .................................................................. 7
Figure 1.4. Five major types of tympanograms ................................................. 9
Figure 1.5. Vestibular schwannoma compressing surrounding
brain structures ............................................................................. 18
Figure 1.6. Head shadow effect illustrating the difference that the frequency
content of the signal has on reaching the contralateral ear ........... 24
Figure 2.1. Photograph of a hard wired PIC 2 CROS aid system
with a remote Control .................................................................... 39
Figure 2.2. WiFi Mic with behind-the-ear hearing aid system ......................... 39
Figure 2.3. Edulink FM receiver and a Smartlink Transmitter ......................... 42
Figure 3.1. Diagram of the three components of the BAHA system ................ 47
Figure 3.2. Diagram of placement of the BAHA in the mastoid region of the
temporal bone ............................................................................... 48
Figure 3.3. Diagram detailing the titanium screw within the mastoid bone ...... 48
Figure 3.4. Side view of Classic 300 ear level sound processor ..................... 52
Figure 3.5. Subject wearing Compact ear level sound processor ................... 53
Figure 3.6. Divino model, ear level sound processor ...................................... 56
Figure 3.7. Intenso model, ear level sound processor .................................... 56
Figure 3.8. Timeline of the introduction of BAHA sound processors ............... 57
Figure 3.9. Photograph of subject’s abutment placement in mastoid Bone .... 60
Figure 3.10. The transfer of sound across to the non-affected cochlea on the
contralateral side from direct bone conduction using the BAHA .. 64
Figure 5.1. Test rod device used in pre-operative evaluation ......................... 78
Figure 5.2. Photograph of Compact BAHA on test band ................................. 78
Figure 5.3. Version of the test band to trial BAHA device ............................... 80
Figure 5.4. Position of speakers for speech testing in noise (S0:N270) .......... 82
Figure 5.5. Position of speakers for speech testing in noise (S0:N90) ............ 82
Figure 5.6. Position of speakers for speech testing in noise (S0:N0) .............. 82
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Figure 6.1. Subject group classification according to aetiology
of hearing loss ............................................................................... 88
Figure 6.2. Individual subject’s PTA3F in each ear ......................................... 95
Figure 6.3. Group A free-field speech testing using AB word lists in quiet ...... 97
Figure 6.4. Group B/C presentation levels (dBHL) for AB words in quiet tested
in the free-field .............................................................................. 99
Figure 6.5. Pre- and post-operative AB words in quiet scores tested in the
free-field ...................................................................................... 100
Figure 6.6. Group B/C pre-operative BKB/A SNR levels ............................... 103
Figure 6.7. Group B/C’s SNR levels using BKB/A sentence ......................... 105
Figure 6.8. Schematic drawing of the internal components of the BAHA ...... 107
Figure 7.1. Adaptation of Killion (1997b)’s data of the relationship between
hearing loss and SNR ................................................................ 132
Figure 7.2. Dry and Store cleaning and drying device .................................. 140
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LIST OF TABLES
Table 1.1. Effects of neuromaturation on selected auditory processes ............ 23
Table 5.1. Calibration of test equipment used during testing procedure .......... 77
Table 6.1. Implanted subject characteristics .................................................... 91
Table 6.2. Non-implanted subject characteristics ............................................. 93
Table 6.3. Implanted subject surgery and device details ................................. 96
Table 6.4. Group A intra-subject scores for AB words Wilcoxon Signed Rank
Test for test band, BAHA and unaided pairs ................................ 101
Table 6.5. BKB/A sentence results for Group A using Wilcoxon Signed
Rank Test..................................................................................... 102
Table 6.6. Group A subjects’ post-operative scores for BKB/A sentences using
Wilcoxon Signed Rank Test ........................................................ 104
Table 6.7. Subjects who had skin reactions requiring treatment .................... 104
Table 6.8. Subjects’ surgical and repair issues ........................................................ 106
Table 6.9. BAHA usage, post-operative complications and repairs of the
implanted subjects ....................................................................... 108
Table 6.10. Implanted subjects APHAB using Wilcoxon Signed Rank Test .... 110
Table 6.11. Non-implanted subjects’ APHAB results using Wilcoxon Signed
Rank Test ..................................................................................... 111
Table 6.12. Implanted subjects GHABP using Wilcoxon Signed Rank Test ... 112
Table 6.13. Non-implanted subjects’ GHABP responses using Paired Samples
T-Test ........................................................................................... 112
Table 6.14 Short-term and long-term SSDQ results from
implanted subjects ....................................................................... 115
Table 6.15 Implanted subjects’ SSDQ responses using Wilcoxon
Signed Ranks Test ....................................................................... 116
Table 7.1. Comparison of implanted GHABP’s mean ± standard deviation of
the four scale scores between two BAHA studies ........................ 146
Table 7.2. Summary of responses to single-sided deafness (SSDQ) across
studies .......................................................................................... 149
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ABBREVIATIONS
AB Max Arthur Boothroyd (word list) - maximum
ABR Auditory brainstem response
ABS Australian Bureau of Statistics
AC Air conduction
ACHA Air conduction hearing aid
AGC Automatic gain control
AGCo Automatic gain control output
ANOVA Analysis of variance
ANSA American National Standards Administration
APHAB Abbreviated Profile of Hearing Aid Benefit
BAHA Bone anchored hearing aid
BC Bone conduction
BCHA Bone conduction hearing aid
BKB/A Bamford/Kowal/Bench - Australian version (sentence test)
BTE Behind-the-ear (hearing aid)
CROS Contralateral routing of signal
CT Computer tomography
CVC Consonant-vowel-consonant (combination)
dB Decibel
dB HL Decibel hearing level
dB SPL Decibel sound pressure level
DSP Digital sound processing
ENT Ear, Nose and Throat (Specialist)
EQ-5D European Quality of Life-5D global survey
ESIA Ear Sciences Institute Australia
FDA Food and Drugs Administration
FM Frequency modulated
GBI Glasgow Benefit Inventory
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GHABP Glasgow Hearing Aid Benefit Profile
HA Hearing aid
HHIA Hearing Handicap Inventory for Adults
HINT Hearing In Noise Test
HL Hearing loss
Hz Hertz
IAM Internal auditory meatus
IEC International Electrotechnical Commission
ILD Interaural level difference
IPD Interaural phase difference
ITD Interaural time difference
ISO International Organisation of Standardisation
kHz Kilohertz
LEHI Lions Ear & Hearing Institute
LHC Lions Hearing Clinics
LKW Loose key word
MRI Magnetic resonance imaging
NAL National Acoustic Laboratories (Australia)
NF2 Neurofibromatosis 2
OAE Otoacoustic emissions
PTA Pure tone average
PTA3F Pure tone average thresholds at frequencies 0.5, 1 and 2kHz
PTA4F Pure tone average thresholds at frequencies 0.5, 1, 2 and 3kHz
QOL Quality of life
SD Speech discrimination
sd Standard deviation
SF-36 Medical Outcomes Study SF-36 Health Survey
SNHL Sensorineural hearing loss
SNR Signal-to-noise ratio
SPL Sound pressure level
SRT Speech reception threshold
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SSD Single sided deafness
SSDQ Single Sided Deafness Questionnaire
TGA Therapeutic Goods Administration
UPSHL Unilateral profound sensorineural hearing loss
VS Vestibular schwannoma
WHO World Health Organisation
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GLOSSARY
AB words: Arthur Boothroyd word lists (1968). Each list consists of ten words
scored as phonemically correct with a possible maximum score of thirty
(Medical Research Council, Institute of Hearing Research, 2008).
Affected ear: Term used to refer to the ear with a hearing loss. In the case of
UPSHL it is the ear that is profoundly hearing impaired and non functional.
Air-bone gap: The difference between the air conduction and bone conduction
thresholds obtained by pure tone audiometry.
Atresia: A congenital condition where there is malformation or absence of the
external ear or pinna (aural atresia) which may include the ear canal,
and /or malformation of the middle ear (Dillon, 2001).
Auditory brainstem response (ABR): An electrical, far-field recordings of
synchronous activity in the auditory nerve and brainstem. It is
characterised by five waveforms which occur within 10 msec following a
presentation of an auditory stimuli to the individual (Bellis, 2003).
Auditory neuropathy: Hearing disorder in which the transmission of signals
from the inner ear to the brain are impaired. Clinical signs are the
presence of otoacoustic emissions with the absence or severely abnormal
auditory brainstem responses (Starr, Picton, Sininger, Hood, & Berlin,
1996).
Audio-vestibular symptoms: Auditory and vestibular symptoms that are
related to ear disorders affecting the cochlear and vestibular system (semi-
circular canals).
Audiologist: A university trained allied health professional specialising in
identifying, diagnosing, treating, monitoring, and rehabilitation services
related to hearing disorders of the auditory and vestibular systems.
Automatic gain control: (AGC) An automatic monitoring circuit used in hearing
aids that reduces gain as a function of the level of the signal that is
amplified. It can be used for compression limiting (substitute for peak
clipping) or to repackage speech into the user’s residual dynamic range
instead of linear processing (Hall & Mueller, 1997).
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Babble noise: Speech weighted noise used in the assessment of speech-in-
noise. It consists of a mixture of different voices to create background
noise.
Bone anchored hearing aid (BAHA) contralateral routing of signal (CROS): The term used by Snik et al. (2005) to describe the BAHA positioned on
the deaf side in subjects with a unilateral profound sensorineural hearing
loss. It functions as a transcranial CROS device. Sounds are transmitted
to the functional contralateral cochlear via direct bone conduction.
Binaural interaction: The integration of input along the auditory pathway after
both ears are presented with sound (Litovsky, 2007).
Cortical auditory evoked potentials (CAEP): Cortical auditory evoked
potentials, reflecting electroencephalographic (EEG) activity in response to
sound stimulation in central auditory pathways, particularly the measured
P1 wave (Peters, 2007).
Ceiling effect: When an individual scores 80% or greater in initial presentation
during testing (Australian Hearing, 2000).
Class D output amplifier: An electronic amplifier that uses switching modes of
transistor to regulate power delivery. Used in devices that require high
power output as they have high power efficiency ratios to weight (Dillon,
2001).
Conformity mark (CE mark): A mandatory conformity mark of the European
Union for consumer safety, health or adhering to environmental impact
requirements.
Congenital: Refers to being present from birth, due to damage and/or defects
to the developing foetus.
Contralateral routing of signal (CROS): A hearing system suitable for people
with unilateral loss, that has hearing aid components at each ear and
requires an electrical connection or wireless transmission (Dillon, 2001).
Dichotic listening: Testing procedure where two different auditory stimuli are
presented in each ear under headphones simultaneously. The subject
may be required to attend to one or both of the messages and asked to
repeat content about either message. It requires communication between
cerebral hemispheres and functional integrity of the temporal lobes. Right
ear advantage (REA) is a term often used as testing with verbal stimuli
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presented dichotically. It was shown that a left sided dominance for
language processing is shown as REA on test results (Bellis, 2003).
Directional microphone: The response of the directional microphone
suppresses noise coming from some directions, while retaining good
sensitivity to sounds arriving from one direction, usually the front. It
achieves this by having two separate inlet ports to the arrival of sound into
the device (Dillon, 2001).
Distortion product otoacoustic emissions (DPOAEs): Distortion product
otoacoustic emissions is an objective auditory test determines the outer
hair cell function of the cochlea. The presence of a DPOAE response
indicates preserved function of the cochlear amplifier (Ito, Endo, Monobe,
Ochiai, & Iwasaki, 2005).
Electrocochleography: A method that measures the electrical potentials
generated in the cochlea, also known as ECochG. Generally involves
measurement of the stimulus–related cochlear potentials (as opposed to
resting potentials) and often includes measurement of the whole nerve or
compound action potentials (AP) of the auditory nerve. The ECochG can
be measured transtympanically via a needle electrode through the
tympanic membrane or extratympanically on sites such as the ear canal or
lateral surface of the tympanic membrane. ECochG are commonly used
as part of the test battery for diagnosis of Meniere’s disease (Ferraro,
2000).
Floor effect: When an individual’s scores are 20% or lower at the initial
presentation of speech testing.
Food and Drugs Administration (FDA): Regulatory body for administration of
drugs, therapeutic goods and food regulations to ensure public safety and
health in the United States of America.
Full thickness skin graft: A surgical technique used in BAHA surgery to create
a skin graft. The graft is raised with fat tissue and hair follicles removed.
Subcutaneous tissue is removed by sharp dissection and bipolar
diathermy is used to control any bleeding (Lekakis, Najuko, & Gluckman,
2005).
Hearing impairment: Hearing loss that affects one or both ears. The
impairment can be graded as complete or partial with various degrees of
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severity such as mild, moderate, severe or profound. “Deafness is the
complete loss of ability to hear in one or both ears” (World Health
Organisation, 2006). Hearing losses can be conductive, sensorineural or
mixed, as well as being defined as either congenital or acquired.
Hearing In Noise Test: A speech test developed to measure word recognition
abilities in quiet and noise. Consists of 25 equivalent 10 sentence lists
that can be presented in quiet or noise with the listener asked to repeat as
much of the sentence as possible. The number of words correct is scored,
but must be repeated verbatim with no pluralisation or verb tense change
accepted as correct (Sargent, Herrmann, Hollenbeak, & Bankaitis, 2001).
Idiopathic: Disease or disorder of unknown cause.
Intralabyrinthine schwannoma: Rare, benign tumour within the labyrinth. The
symptoms are non-specific audio-vestibular symptoms and can be
confused with Meniere’s disease. Magnetic resonance imaging is used in
the detection of intralabyrinthine tumours (Saeed, Birzgalis, & Ramsden,
1994).
Lateralisation: Form of localisation on the horizontal plane. It is the laboratory
version of localisation as a means of studying judgements of distance and
direction of a sound source (Moore, 2003).
Localisation: The ability to discriminate and orient to where a sound originates,
based on binaural hearing cues (Sargent et al., 2001).
Loose key word scoring: A scoring technique used in the BKB/A sentences.
Mastoid: The mastoid portion forms the posterior section of the temporal bone.
Microtia: A congenital abnormality of the outer ear (pinna), which can be
unilateral or bilateral.
Middle fossa surgical approach: One of the skull base surgical techniques
used in the removal of vestibular schwannomas.
Omni-directional microphone: The response of the omni-directional
microphone is a near perfect sphere in three dimensions. It is the opposite
to a directional microphone, as it has a single port and a polar diagram
that is in the shape of a circle (Dillon, 2001).
Otitis externa: An inflammation or infection of the outer ear and ear canal,
causing pain, ear discharge and swelling. The inflammation can be
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dermatitis without microbial infection or it can be caused by active bacterial
or fungal infection. It can be caused by trauma to the skin in the ear canal
or prolonged water exposure in swimming or extreme humidity. Untreated
otitis externa with perforation can lead to complications such as
cholesteatoma or necrotizing external otitis (malignant otitis externa) with
elderly individuals with uncontrolled diabetes or severely compromised
immune system (Wikipedia contributors, 2009a).
Otitis media: An infection or inflammation of the middle ear, caused by a
bacterial or viral infection of the upper respiratory tract.
Otoacoustic emissions (OAEs) testing: Audiological testing procedure
clinically used to measure the outer hair status of the cochlear from
evoked stimulus, including pure-tones, click (broadband) or tone burst
stimulus. Commonly used to as a part of universal hearing screening
programmes for newborn babies. OAEs are also used with difficult to test
subjects and young children, as well as part of a test battery for the
differential diagnosis of the cochlear and higher level hearing losses such
as auditory neuropathy (Wikipedia contributors, 2009b).
Otolaryngologist: A medical doctor that specialises in diseases and disorders
of the ear, nose, throat as well as the head and neck. Also known as
Head and Neck surgeon; an Ear, Nose and Throat (ENT) specialist or an
otolaryngologist or otorhinolaryngologist.
Phonemes: The individual sounds within a word. For example, the word “cat”
has three phonemes.
Presbyacusis: The deterioration in hearing, particularly in the higher
frequencies, as a characteristic of the ageing process. The hearing loss is
sensorineural in nature and the hearing loss worsens with age in most
people, even with the absence of significant noise exposure (Grant, 1999).
Retrocochlear pathology: Any pathology diagnosed along the auditory
pathways beyond the cochlea, such as vestibular schwannomas or
auditory neuropathy. Generally diagnosed by magnetic resonance
imaging and/or auditory brainstem responses.
Split thickness skin graft: A surgical technique used in BAHA surgery using a
dermatome. This graft includes the epidermis and varying amounts of
dermis. (Lekakis et al., 2005)
xxiii
Skull base surgery: The skull base is a term used to describe the area of the
skull on which the brain rests. Disorders within the skull base can be
vascular lesions or tumours of the cranial nerves. Skull base surgery
involves operating within one of the three regions of the skull; anterior,
middle or posterior fossa depending on the size and type of lesion to be
removed (Maroon, 2005).
Sleeping (spare) fixture: A spare titanium BAHA implant that is surgically
placed in the mastoid region of the temporal bone. It is usually placed in
children receiving a BAHA as a back up to implant failure.
Speech reception threshold (SRT): A speech reception threshold at which the
speech level or SNR at which a specified level of performance, such as
50% correct is achieved (Dillon & Ching, 1995).
TDH-39: Standard air conduction headphones that are calibrated to a specific
audiometer. They are not interchangeable between audiometers unless
recalibrated.
Temporal processing: Testing can be of gap detection abilities. Temporal
encoding occurs in the peripheral auditory system and represented at
various levels throughout the auditory pathways. The extraction and
analysis of auditory temporal cues are a central function (Bellis, 2003).
Therapeutic Goods Administration (TGA): Australian regulatory body for
administration of drugs, therapeutic goods and food regulations to ensure
public safety and health.
Test band: A metal headband used to attach the external sound processor
during pre-operative assessments. A modified version of the test band is
used to trial the sound processor in work and/or home environments.
Test rod: A device comprised of hard plastic with a BAHA abutment embedded
on the top. Used in the pre-operative assessment for BAHA to gauge user
benefit when the BAHA sound processor is attached to the abutment part.
Transducer: The vibrating part within a bone conduction headphone or bone
anchored hearing aid.
Transcranial: Transfer of sound across the cranium or skull, for example
transcranial hearing aids.
Translabyrinthine surgical approach: One of the skull base surgical
techniques used for the removal of tumours found in the posterior fossa of
xxiv
the skull base. The region of the cerebellopontine angle is accessed
through the mastoid region and labyrinth of the ear to remove tumours in
this area (Maroon, 2005).
Top-down factors: Processes that filter down a system using higher level
knowledge to facilitate lower level processes (Parkin, 2000). Speech
sounds are recognised cognitively and processed “top-down” to give
linguistic meaning to speech. Top down processing allows cognitive
interpretation of the intent of the speaker, allows prediction of remaining
structure and content of sentences as they occur (Schum & Beck, 2008).
1
Chapter 1: Introduction
Individuals diagnosed with a profound sensorineural hearing loss in one ear,
commonly known as a unilateral hearing loss, have always posed difficult
clinical questions for audiologists and otolaryngologists in regard to their
management. It has been reported that annually there are about 7500 new
cases of unilateral profound sensorineural hearing loss (UPSHL) in the United
Kingdom (Baguley, Bird, Humphriss, & Prevost, 2006). However, the
rehabilitation options for individuals with this type of hearing loss are limited due
to lack of technology and the very nature of the hearing loss. The individual with
UPSHL, is able to compare the artificial acoustic input from hearing aids or
assistive listening devices which are the primary rehabilitation choices, to the
“natural” sound they perceive in their normally functioning ear. This can lead to
higher expectations (Hill, Marcus, Digges, Gillman, & Silverstein, 2006). Thus
the hearing difficulties experienced by many individuals with a UPSHL have not
been effectively addressed.
Traditionally, the options offered to individuals with a UPSHL were to monitor
the hearing in the good ear, counselling on listening strategies, and/or fit an
amplification device such as a contralateral routing of signal (CROS) hearing aid
(Dillon, 2001). In recent years, a new application of a well-known rehabilitation
device became available to individuals with this type of hearing loss. The bone
anchored hearing aid (BAHA, designed by Nobel Biocare, Gothenberg, Sweden
and now marketed as Baha ® by Cochlear Limited, Australia) is an implantable
device that can be fitted in the mastoid bone of the ear with the profound
sensorineural hearing loss (Bosman, Hol, Snik, Mylanus, & Cremers, 2003;
Niparko, Cox, & Lustig, 2003; Wazen et al., 2003; Weber, 2002). Currently, this
is the only available implantable device which uses direct bone conduction to
transfer sound from the profoundly hearing impaired ear to the contralateral
better hearing ear.
Recently, there have been reported cases of implanting a standard cochlear
implant in individuals with a UPSHL. However, this has been to treat
incapacitating unilateral tinnitus and not the hearing loss (Van de Heyning et al.,
2
2008). This study has focused on adults with a UPSHL who have been fitted
with the BAHA.
The BAHA has been successfully used as a rehabilitation tool for over thirty
years with individuals who are unable to use conventional air conduction
hearing aids due to chronic conductive hearing loss, and/or mixed hearing
losses, for anatomical or medical issues such as an atretic outer ear or
persistent otitis externa. There are 50,000 BAHA users worldwide using the
BAHA device for a range of hearing losses (Tjellstrom, 2008). In 1999,
researchers in France reported on their study of applying the BAHA to
individuals with unilateral total deafness (Vaneecloo et al., 2001). By 2003, the
BAHA device had been applied to between 250 to 400 individuals with UPSHL
worldwide, predominantly in France, United Kingdom and the United States of
America (Entific Medical Systems, 2003b; Roberts, Mitchell, & Parker, 2005). In
Australia, the first BAHA fitted for a UPSHL was in November 2002 at the Ear
Sciences Institute of Australia (ESIA), at the time known as the Lions Ear &
Hearing Institute (LEHI).
Although the principles of the BAHA rehabilitation procedure are the same
across the various countries fitting the device, standardised testing of potential
candidates using normalised speech tests with an Australian accent and
vocabulary has not been validated. In addition, evaluation of the efficacy of this
device as a treatment strategy for UPSHL has not been conducted, as it is a
relatively new application of the BAHA. Little is known about the long-term
outcomes of individuals who are fitted with the BAHA for their UPSHL.
This study aimed to develop protocols using standardised speech tests
developed for the Australian population to evaluate the long-term outcomes of
individuals fitted with the BAHA to rehabilitate their UPSHL. The results will
assist audiologists and otolaryngologists alike to make scientifically informed
decisions regarding the clinical management of individuals with UPSHL.
3
1.1 Unilateral profound sensorineural hearing loss (UPSHL)
There are many different terms used in the literature to describe a UPSHL:
single sided deafness (SSD, a registered trademark of Cochlear Limited), total
monaural deafness, unilateral total (sensorineural) deafness (Snik et al., 2005);
(Vaneecloo et al., 2001), monaurally deaf (Van Wanrooij & Van Opstal, 2004),
ipsilateral sensorineural deafness (Vermeire et al., 2008), and unilateral
deafness (Lin et al., 2006; Van de Heyning et al., 2008). In audiological terms,
this type of loss is generally referred to as a UPSHL, and is defined as one
affected ear with hearing thresholds to the profound level whilst the non-affected
ear has hearing thresholds within normal limits. The term SSD was not used as
it is a broad term, which can be used to define a hearing loss in one ear that can
range in severity from mild to profound, as well as refer to unilateral conductive,
sensorineural or mixed losses.
Worldwide, no consensus exists on the definition of normal hearing. The
American National Standards Institute (ANSI, 1989) states that normal hearing
is indicated by hearing thresholds in the range of 0 to 25dB HL to describe
normal hearing limits (Sataloff & Sataloff, 1993). In Australia, it is generally
accepted that thresholds of hearing up to and including 20dB HL are regarded
as the clinical normal hearing region for adults. A profound hearing loss is
indicated by a hearing loss of 91dB HL or greater as tested by pure tone
audiometry techniques (Australian Hearing, 2008a; Wilson, Walsh, Sanchez, &
Read, 1998). Figure 1.1 shows an example audiogram of a UPSHL with no
detection of air or bone conduction thresholds at the maximum limits of the
audiometer in the left ear.
Depending on the aetiology, in addition to pure tone audiometry, the hearing
loss can also be investigated by objective diagnostic techniques such as
magnetic resonance imaging (MRI), computer tomography (CT) scans,
automatic brainstem response (ABR), electrocochleography (ECochG), and
otoacoustic emissions (OAEs) testing (Hill et al., 2006). A UPSHL has medical
diagnostic significance as asymmetrical hearing thresholds between ears are
not considered as a normal presentation in regards to hearing loss (McLeod &
Upfold, 1999). A UPSHL is localised to the cochlea and/or higher auditory
4
pathways up to the level of the auditory nuclei, including the bipolar ganglion of
the eighth cranial nerve (Sataloff & Sataloff, 1993). The hearing loss may be
congenital or acquired, and is permanent due to its sensorineural component.
Figure 1.1. Audiogram of left UPSHL.
1.1.1 Types of hearing loss
There are three components of the ear: the outer, middle and inner ear. These
parts of the ear can be affected by various diseases, injury and genetically
inherited conditions to cause a multitude of hearing losses. The three major
types of hearing loss are: conductive, sensorineural and mixed hearing losses.
A conductive hearing loss can be congenital or acquired, and affects the
transmission of sound by a blockage or damage to outer part and/or the middle
ear system as shown in Figure 1.2. Within the ear canal, infections such as
otitis externa can cause swelling, therefore affecting effective transmission of
sound to the tympanic membrane (eardrum) onto the middle ear. There can
also be issues within the middle ear cavity when the movement of the ossicles
5
(middle ear bones) is affected by fluid in the normally air-filled cavity from an
infection such as otitis media, or due to anatomical structural problems as
otosclerosis. These issues in the outer and/or middle ear prevent sound from
being effectively conducted through to the cochlea and the auditory nerve to
higher cortical structures. Conductive hearing losses can be transient in nature
such as occurs with otitis externa or otitis media. However, it can also be
chronic in the cases were infections have caused damage to the structural
integrity of the middle ear system or due to congenital malformation of the outer
and/or middle ear system such as atresia or microtia (malformed pinna or
auricle). Generally, conductive hearing losses can be treated medically or
surgically.
Figure 1.2. The anatomical components of the ear.
Note. From (Virtual Medical Centre, 2007)
A sensorineural hearing loss refers to an affected sensory system and/or neural
system as shown in Figure 1.2. The sensory system includes the cochlea and
its fine architecture of hair cells. The neural system involves the auditory nerve
and vestibular nerves, their myelinated sheath, and the pathways to the auditory
cortex. If there is damage to either or both of the sensory or neural
components, the hearing loss is usually permanent, being medically and/or
6
surgically irreversible. The loss affects the quality and quantity of sound
reaching the auditory cortex. The sensorineural hearing loss results in the
higher cortical processing levels receiving a distorted signal. This leads to
issues of clarity and incomplete sound needing to be interpreted by the
individual. A mixed hearing loss refers to the combination of a conductive and a
sensorineural hearing loss. For example, it can occur when a sensorineural
hearing loss from the ageing process (presbyacusis) is compounded by
infections of the outer ear canal causing swelling and inflammation blocking the
transmission of sound, such as chronic otitis externa. Some conditions such as
otosclerosis, which start as a conductive hearing loss, can later present as a
mixed hearing loss due to involvement of the cochlear structures as the
condition progresses.
1.1.2 Audiological test battery
As mentioned previously, a UPSHL is diagnosed by pure tone audiometry. This
testing is conducted in soundproof conditions such as an audiological booth. Air
and bone conduction thresholds are obtained in adults and older children by
presenting pure-tone through an audiometer in an ascending and descending
technique, known as the modified Hughson-Westlake procedure. This
audiometric testing technique is designed to obtain the individual’s hearing
threshold, or just detectable hearing level. The individual is required to respond
to air conduction stimuli that are presented to each ear in an adaptive procedure
at suprathreshold and below thresholds at various frequencies between 0.25kHz
and 8kHz. The audiologist accepts two out of three threshold responses from
the individual at a particular intensity measured in decibel hearing level (dB HL)
for each frequency in each ear to determine the threshold. The thresholds are
plotted on an audiogram as shown in Figure 1.3. The same technique is used
to obtain bone conduction thresholds but with a smaller range of frequencies,
usually 0.5kHz, 1kHz, 2kHz and 4kHz. Threshold testing is conducted with the
interoctaves or intermediate frequencies such as 0.75kHz, 1.5kHz, 3kHz and
6kHz if there is a 20dB HL difference between the standard frequencies that are
tested.
7
Air and bone conduction clinical masking is performed when there is a
significant difference between the thresholds in each ear such as an
asymmetrical hearing loss and a UPSHL. There are set predetermined
difference levels between the air conduction and bone conduction thresholds
that will require the input of narrow band noise (masking noise) into the non-test
ear. The non-test ear requires this signal to ensure that cross-over of the stimuli
does not interfere with the thresholds being determined in the tested ear.
Audiologists generally perform clinical masking according to the Hood
procedure. Similarly, speech masking is conducted with speech testing under
headphones, however the masking noise is a speech-weighted noise instead of
narrow band noise.
Figure 1.3. Degrees of hearing loss. NB: Shaded areas on an audiogram show the areas of normal hearing that overlap when they have been divided into paediatric and adult. Note. From (Center for Hearing and Communication, 2008) In addition to pure-tone air and bone conduction audiometry, impedance
audiometry and evaluation of speech understanding is normally conducted as
part of the standard audiometric test battery. Impedance or immittance
audiometry consists of tympanometry and acoustic reflexometry.
Tympanometry is a measure of tympanic membrane impedance or compliance.
8
The plot presents with pressure along the X axis (measured in daPa) and static
compliance along the Y axis (measured in mmH20) (Troost & Walker, 1998a).
The Jerger-Linden classification system for tympanograms is usually used,
which classifies the plot as a Type A, B, C, As and Ad as shown in Figure 1.4
(Fowler & Shanks, 2001). The peak of static compliance is generally the critical
feature that differentiates the different description of the tympanograms along
with measurements of ear canal volume and middle ear pressure. Type A
tympanograms are recorded in ears with normal hearing thresholds. They are
also associated with a sensorineural hearing loss in an otherwise healthy ear. A
Type B tympanogram is flat or rounded; indicating either middle ear disorders
such as a fluid-filled middle ear system or a perforated tympanic membrane,
and is often associated with a conductive hearing loss. Type C describes a
tympanogram that has a peak in the negative middle ear pressure range; Type
As describes a tympanogram with a shallow peak, and Type Ad has a deep or
high peak (Fowler & Shanks, 2001).
Acoustic reflexometry obtains acoustic reflex thresholds. That is the lowest
intensity of a pure tone stimulus that is required to elicit a contraction of the
stapedius acoustic tympani muscles. This contraction is to protect the hearing
system from loud and potentially damaging stimuli. Ipsilateral reflexes are
measured by stimulating one ear and recording the responses from the same
ear. Normal acoustic reflexes occur between 70 and 100 dBSPL. Acoustic
reflexes are used as part of a test battery to confirm audiometric thresholds and
tympanometry results that have been obtained, as middle ear abnormalities,
retrocochlear pathology or a significant sensorineural hearing loss can obliterate
the acoustic reflex response (Troost & Walker, 1998a). An individual with
UPSHL would be expected to have would be expected to produce normal
ipsilateral acoustic reflexes in the non-affected ear, with an absence of
ipsilateral acoustic reflexes in the affected ear.
9
Figure 1.4. Five major types of tympanograms.
Note. From (Troost & Walker, 1998b).
Evaluation of speech understanding at suprathreshold levels produces a
“speech discrimination score” or “word discrimination score” (Thibodeau, 2000).
With standard audiometric testing, an audiologist will assess suprathreshold
levels by presenting a series of single consonant-vowel-consonant (CVC) words
in quiet to obtain a speech recognition score at the prescribed level dependent
on the pure tone audiometry thresholds. Each ear is tested separately under
headphones. The subject verbally repeats what they thought they heard, and
the audiologist scores the response by the amount of correctly repeated
phonemes.
For testing speech understanding of single words, the word lists generally used
in Australia are the Arthur Boothroyd word (or AB words) lists (Boothroyd,
1968), which are isophonemic, i.e., word lists that contain the same proportion
of phonemes in each list (Dillon & Ching, 1995). On most occasions
audiologists will find the individual’s AB maximum (Max) score in each ear
representing the level at which the subject is expected to respond with the
highest speech recognition score to correspond to their hearing thresholds.
This test conducted under headphones is also used as part of the test protocols
10
to verify the audiometric thresholds in each of the tested ears. For example,
individuals who are malingering with their pure tone thresholds may have
inconsistent speech discrimination scores; or retrocochlear pathology such as
auditory neuropathy may result in usual pattern of speech discrimination
responses that are not consistent with the individual’s thresholds. It is common
practice in Australia to use the term “speech discrimination (SD) score” for all
measures of identification or recognition of speech at suprathreshold levels,
whereas the technically correct term is either “speech recognition score” or
“word recognition score” (Dillon & Ching, 1995).
The SD score is also used to evaluate whether further investigation or referral is
required to rule out retrocochlear pathology, as well as assisting audiologists in
determining whether the fitting of conventional air conduction aids would be
beneficial (Dillon & Ching, 1995). Fitting hearing aids to individuals with poor
speech discrimination and/or profound sensorineural hearing thresholds can
produce limited outcomes. Using the AB Max score to help decide whether
amplification of a particular hearing loss may be beneficial is somewhat
arbitrary. Dillon (2001) stated that a minimum cut-off score used by audiologists
to determine hearing aid candidates from non-candidates is not valid due to the
poor correlation between unaided speech testing and hearing aid outcomes.
One major problem with speech tests is that hearing aids give a different
frequency response compared to the flat frequency response of amplified
speech under headphones (Dillon & Ching, 1995). Another problem is that
speech testing in the pre-fitting situation is normally conducted in quiet, clinical
conditions, which is an unrealistic setting. Therefore, it is not possible to make a
direct comparison between the unaided speech score obtained under
headphones and the aided benefit from testing in free-field conditions.
Bentler (2000) supported this by reporting that there is poor correlation between
the predicative nature of traditional pre-fitting speech measures, which are
normally done in quiet settings, and hearing aid fitting outcomes. She therefore
suggested that unaided and aided speech perception testing be conducted in
noise to determine the signal-to-noise ratio (SNR) for 50% performance, and
that this may instead present the greatest insight into the individual’s auditory
11
integrity. This testing requires the subject to repeat the stimulus verbally at
threshold level and is referred to as the speech recognition threshold (SRT).
Testing of this type evaluates whether the auditory filters of the auditory system
can separate the intended signal from the background noise, and consequently
can be used as part of pre- and post-fitting evaluations.
There are many speech tests available to evaluate speech understanding in
noise. However, many of the speech tests in common use can not be
considered for research for the following reasons: (i) the speech material is not
digitally recorded and so has to be presented via a “live” voice. If there is more
than one tester, this would lead to inaccuracy with the results and difficulty in
obtaining a constant signal of the voice due to normal individual speech
fluctuations; (ii) recorded speech material with either an American or British
accent, so this is not as appropriate for the Australian population; (iii) tests that
have insufficient number of sentence lists; and (iv) tests that are too difficult, for
example, consonant-vowel-consonant (CVC) monosyllabic word lists have less
salient features for the listener than a sentence test, particularly for testing in
background noise.
Despite the consensus amongst researchers and audiologists that individuals
with a UPSHL have difficulty understanding speech in noise, administrating
tests evaluating this is not part of standard pre-fitting audiological evaluation
(Smits, Kramer, & Houtgast, 2006). It does occur in specialised cochlear
implant clinics, but not for standard hearing aid fittings. There are many
different speech materials available for assessing understanding of sentences in
noise. One such test that is commonly used in Australian cochlear implant
clinics is the Bamford-Kowal-Bench/ Australian Version (BKB/A) sentences lists
(Bench & Doyle, 1979; Bench, Kowal, & Bamford, 1979) because they have
been recorded with male voice with an Australian accent, are easy to use,
calibrated and can be presented with four-speaker babble.
The BKB/A sentences are predominantly used in the clinical situation for the
evaluation of aided versus unaided performance with cochlear implant subjects,
as well as part of research protocols studying hearing impaired populations, and
12
therefore may be appropriate for UPSHL. Initially the BKB/A sentence test was
designed to be used with severe to profoundly hearing impaired children. It is
clinically appropriate to use with normal hearing children from six years of age,
but can also be used with hearing impaired adults. Lists 8, 10, 16 and 20 were
significantly different from other lists in terms of difficulty (Australian Hearing,
2000; Keidser et al., 2002) and therefore should be excluded. The fifty
embedded target words were scored using the Loose Key Word (LKW) method.
LKW method allows a grammatical error for the key word to be accepted, for
example “running” instead of “ran” or accepting the singular plural “lady” instead
of plural that is denoted by a high frequency /s/ sound, as in “ladies”. This
method has been found to result in less scorer error in relation to the tester’s
perception of the listener response than other scoring methods (Bamford and
Wilson, in Bench et al., 1979).
Thorton and Raffin (1978) have shown that sensitivity of speech tests depends
on the number of trials administered. Their model demonstrates that
performance variability is greatest in the middle range of scores and less at the
extremes. The BKB/A sentence list is a 50-item list, and therefore when
determining 50% as the initial speech recognition score, the probability of this
obtaining this score is difficult, with a score being likely to fall between 32-68%.
Guided by Thornton and Raffin’s (1978) critical differences model, for the given
number of test items, values within each range are not significantly different
from the initial speech recognition score (p>.05) (Thibodeau, 2000). Therefore if
the two scores are not significantly different according to the model, the two can
be averaged to represent the speech recognition performance. To observe a
treatment effect, the level had to fall outside the range given by Thornton and
Raffin (1978)’s model.
In cases of bilateral severe to profound hearing losses, however, Dillon (2001)
pointed out that the benefits of traditional hearing aid amplification to assist with
speech understanding and voice monitoring cannot be ignored. This is a valid
point for individuals with a bilateral, progressive sensorineural hearing loss, or
even those with a congenital profound sensorineural hearing loss who have
been consistent hearing aid users. However, for those individuals with a
13
UPSHL, the aforementioned advantages of conventional amplification are not
applicable because of the normal hearing levels in the non-affected ear and
speech discrimination that is typically very poor, often below 20% correct.
There is an issue to whether applying amplification into the affected ear via a
conventional hearing aid to produce a distorted signal interferes with the clear
input received by the normal hearing in the non-affected ear. Therefore, the
audiologist is faced with a difficult clinical decision when dealing with a UPSHL.
The audiologist must decide whether to aid this type of hearing loss, and/or
determine what rehabilitation options, if any, are most suitable for each
individual and their respective circumstances.
1.2 Incidence of UPSHL
It is difficult to state the exact percentage of the population presenting with a
UPSHL. In Australia, the Blue Mountains Hearing Study, which studied a
population of 55 year olds and older, showed that 0.5% of the population
sample had a bilateral profound hearing loss (>90dB HL) (Sindhusakea et al.,
2001). Another demographic study of hearing impairment in the Australia,
suggested that 22% of the population over the age of fifteen had a hearing loss.
The study gives the figure of 6.3% of subjects having a unilateral hearing loss
greater than 21dB HL (average of 0.5kHz, 1kHz, 2kHz & 4kHz) (Wilson et al.,
1998). As the figures relate to all unilateral hearing losses greater than 21dB
HL, the number of individuals who could be categorised as having a UPSHL
would be most likely to be considerably less. Reports on both of these studies
do not record the number of individuals with a UPSHL or specify whether the
unilateral hearing loss was congenital or acquired. Therefore, as it stands, the
percentage of the Australian population with a UPSHL has not been determined.
Overseas figures of proportion of the population with a UPSHL are not well-
defined either. It is estimated that there are 10,000 people in the United
Kingdom alone with “single sided deafness” (Shanker, Davison, & Johnson,
2004), however this estimate does not define whether it is UPSHL, and what
percentage of the individuals with the hearing loss resulted from congenital or
acquired manifestation. Colletti, Fiorino, Carner & Rizzi (1988) conducted a
study of 31,235 individuals having a hearing test in a clinical setting between
14
1970 and 1987 at the ENT Department of the University of Verona, Italy.
Eleven percent of these individuals presented with unilateral hearing loss, of
which 49.5% had a sensorineural loss. They examined the degree of hearing
loss in a smaller subgroup, reporting that 71 of 1583 (4.5%) of these individuals
had a UPSHL. This figure of 4.5% only represents a small percentage of the
Italian population as these individuals presented to an ENT clinic, therefore had
a specific hearing problem. It gives an example of the clinical presentation to
ENT clinics, but not a broader demographic representation of UPSHL in the
population.
1.2.1 Incidence of congenital UPSHL
The incidence of children born with a congenital unilateral hearing loss ranges
from 2 per 1000 to 13 per 1000 in the United States of America (Bentler, 2000;
Bess & Tharpe, 1986). A smaller study in Western Australia, as part of a
newborn screening programme has been reported by Krishnaswamy (2008).
He found that 0.72 per 1000 live births were diagnosed with a unilateral
sensorineural hearing loss. However, this figure only reflects a 50% capture
rate of the total live births in Western Australia and does not specify the severity
of the unilateral hearing loss. With some genetic disorders, it is difficult to
categorise the hearing loss as congenital or acquired. The genes that
predetermine particular hearing losses may be present at birth, but expression
of the loss does not occur until a later stage of the individual’s development.
1.2.2 Incidence of acquired UPSHL
When determining the prevalence of acquired UPSHL, it is difficult to gauge the
extent of prevalence in the population. For example, despite there being
documentation of the occurrence of Meniere’s disease, there are no specific
numbers of those individuals who have a UPSHL resulting from Meniere’s
disease as the hearing loss can fluctuate before the final stage of “burn-out”.
Similarly when looking at sudden idiopathic sensorineural hearing loss, studies
often report incidence of long-term hearing loss, but the degree of final hearing
loss is not reported, so it can not be assumed that it is a UPSHL.
15
Instead, the post-operative UPSHL resulting from a vestibular schwannoma
(VS) removal with the translabyrinthine surgical approach is often quoted when
estimates of the occurrence of acquired UPSHL. This is due to records of VS
surgery being documented through the use of Medicare codes in Australia
(McLeod, Upfold, & Taylor, 2008). This surgical technique is preferred for
individuals with large VS and poor pre-operative hearing as this approach has a
high likelihood of no residual hearing post-operatively.
The translabyrinthine approach for the tumour removal may also be selected by
the surgeon as it has advantages of good identification of the facial nerve,
minimum cerebellar retraction, lowest morbidity with spinal fluid leaks and post-
operative headaches (Brackman & Green, 2008). Other surgical techniques for
tumour removal, such as the middle fossa approach may result with
preservation of hearing after the tumour is removed.
The incidence of VS in the Australian population is estimated to be about 1.71
per 100 000 individuals (McLeod et al., 2008), with approximately 300 new
cases of VS diagnosed each year (Acoustic Neuroma Association (NSW),
2005). A review by Edwards, Schwartzbaum, Lonn, Ahlbom & Feychting (2006)
reported the incidence of VS to be 1-20 per 100 000 per year in Scandinavian
countries.
1.3 Congenital causes of UPSHL
A UPSHL can be genetically inherited, and may arise from including anomalies
of the bony structures of the inner ear, such as Mondini dysplasia or large
vestibular aqueduct syndrome and/or internal auditory meatus (IAM). Enlarged
vestibular aqueduct syndrome confirmed by radiological examination is a
congenital condition. The UPSHL and balance disorder associated with this
condition generally occur as a consequence of a minor head trauma.
Another group of individuals who present with a UPSHL are those with isolated
cochlear nerve aplasia (occurring in the form of auditory neuropathy), without a
narrow internal auditory meatus (IAM). A group of such individuals were
described in a paper by Ito, Endo, Monobe, Ochiai & Iwasaki (2005). The
16
researchers concluded that some subjects with a UPSHL may have had the
aetiology of their hearing loss misdiagnosed as a more common aetiology (a
viral infection such as mumps), if MRI or OAEs procedures had not been
performed. The MRI has allowed better imaging of the anatomical structures
within the temporal bone to define abnormalities. In the case of these
individuals, OAEs would be present, whereas with a profound sensorineural
hearing loss they are expected to be absent. These imaging and diagnostic
procedures were not readily available when some of the adult cases in this
present study were first diagnosed with their UPSHL. Ten years ago these
diagnostic techniques were in their infancy and/or there was limited access to
this medical imaging and diagnostic audiological testing. However, it is now
routine to perform a MRI on individuals who present with a UPSHL, even if it
was initially diagnosed in childhood, if this type of imaging technique was never
performed.
Some causes of congenital UPSHL can be due to the cross-placental viral
infection in the developing foetus. Viruses that may result in bilateral or
unilateral hearing loss include toxoplasmosis, rubella or cytomegalovirus (CMV)
(Fowler et al., 1997).
1.4 Acquired UPSHL
An acquired UPSHL, which may result from trauma, neoplasms, metabolic
disorders, infections, ototoxicity, immunological reactions or idiopathic cause is
commonly seen by medical and allied health professionals dealing with hearing
loss in their clinics (Ruckenstein, 2000). Some acquired UPSHL may be a
combination of one or more of the listed factors above.
1.4.1 Trauma
UPSHL can also be acquired through head trauma or complications from ear
surgery, resulting with an insult to the inner ear or auditory nerve. For a
unilateral loss to occur, Ghossaini (2006) reported that the injury sustained with
trauma needs to lead to cochlea damage, such as a fractured temporal bone
damaging the cochlea or injury to the vestibular-acoustic nerve (VIII). Head
trauma is more likely to cause a SNHL with a transverse fracture than a
17
longitudinal one. Haemorrhage into the inner ear as a result of temporal bone
trauma may also lead to a sudden UPSHL (Grant, 1999).
Barotrauma results in an ear injury when the ear structures are exposed to
extreme pressure changes, and the inability of the system to equalise the
pressure of the air-containing spaces of the ear to that of the external
environment. Large, sudden changes to the middle ear pressure can be
transmitted to the inner ear resulting in cochlear damage and a UPSHL. This
can occur when the ear is subjected to implosive or explosive mechanisms
related to the round or oval window (Bentz, 2008).
1.4.2 Metabolic
Vascular disease or vascular lesions with haemorrhage, thrombosis, and
vasospasm of the terminal branch of the anterior-inferior cerebellar artery or
cochlear vessels can result in a UPSHL (Grant, 1999).
1.4.3 Neoplasms
A neoplasm is any abnormal growth of new tissue or a proliferation of cells no
longer under physiological control. These may be benign or malignant.
Tumours affecting the hearing system include vestibular, intracochlear or
trigeminal schwannomas which may cause a UPSHL. Vestibular schwannomas
(VS) form the greatest number commonly associated with UPSHL. They can be
sporadic or hereditary, in the case of the autosomal dominant disorder,
Neurofibromatosis II (NFII). Eighty-five percent of NFII patients show bilateral
tumours on the MRI (Olschwang, 2002). However, the person diagnosed with
NFII may have a period where they have a UPSHL due to the removal of one
tumour resulting in the profound hearing levels on one side, and the presence of
a small asymptomatic tumour on the contralateral nerve, which does not affect
the hearing thresholds in that ear at that stage.
A unilateral progressive sensorineural hearing loss is an early and main feature
of a VS (Forton, Cremers, & Offeciers, 2004). Vestibular schwannomas are
classified as benign tumours of the nerve root sheath of the superior or the
inferior vestibular, or rarely, the cochlear nerve (Grant, 1999). They generally
18
grow slowly at the inner entrance of the IAM. Van Leeuwen, Braspenning,
Meijer & Cremers (1996) reported that 96% of their subjects reported poor
hearing before VS surgical excision, while Obholzer, Rea & Harcourt (2004)
reported 90% of subjects with VS had audio-vestibular symptoms. Similarly,
Jia, Marzin, Dubreuil & Tringali (2008) reported that 93% of subjects with
intralabyrinthine schwannomas presented with a hearing loss. The reason that
hearing loss occurs with VS is not fully known, but Forton et al. (2004)
suggested that it is due to the tumour compressing the blood supply to the
cochlea, and on the cochlear nerve itself as shown in Figure 1.5. Mahmud,
Khan & Nadol (2003) reported that VS caused hearing loss and poor speech
discrimination as a result of degenerative changes in the inner ear, including
endolympathic hydrops, atrophy of the stria vascularis and spiral ligament, as
well as proteinaceous precipitates in ear fluids. The authors were unable to
describe or explain the mechanisms that caused these changes.
Figure 1.5. Vestibular schwannoma compressing surrounding brain structures.
Note. From (Man-Wook Seo, 2007).
Although the growth of a VS is slow, its impact over time on surrounding
anatomical structures increases, and treatment includes surgery, radiotherapy
and observation. If the translabyrinthine surgical procedure is used, a UPSHL is
nearly always the outcome, although there are reported cases of small VS being
19
removed via the translabyrinthine procedure with preservation of auditory nerve
function (Kiyomizu et al., 2006).
Other neoplasms such as trigeminal or intracochlear tumours can result in
UPSHL. Benign trigeminal nerve schwannomas represent 0.2% to 0.4% of all
intracranial tumours and are differentiated by their anatomical location via
imaging such as a MRI. Their growth needs to be very extensive to cause a
UPSHL.
1.4.4 Infections
Due to the anatomical structure and organisation of the hearing system, it is
particularly vulnerable to metabolic influences as the second-order neurons of
the auditory pathway are within the brainstem. With its requirements for high
levels of oxygen and glucose due to high vascularity, the cochlear nucleus is
susceptible particularly in early development and post-natal period (Fisch,
1983). Causes of acquired UPSHL include the following: post-natal viral
infections that have affected only one ear such as mumps, measles, pertussis
(whooping cough), rubella and varicella-zoster (chicken pox); acute labyrinthitis
(Nageris, Popovtzer, & Tiqva, 2003); and bacterial meningitis (unilateral or
bilateral profound sensorineural hearing loss occurs in 5 to 30 per cent of
survivors (Goycoolea, Iniguez, & Perez, 1995). Medical conditions such as
Ramsay Hunt Syndrome results in a hearing loss from an infection of the herpes
zoster virus to the hearing system.
A UPSHL may result as the sequelae of otitis media that initially starts with a
bacterial infection, however in chronic conditions where a cholesteatoma has
developed, the infection can erode structures within the middle ear and inner
ear, or lead to bacterial meningitis.
1.4.5 Ototoxicity
Medications such as amino glycosides; diuretics, particularly loop diuretics;
salicylates; cytotoxic chemotherapeutic agents (for example, cisplatium) have
been reported to cause hearing loss in humans.
20
Diseases of the inner ear may be directed treated by ototoxic drugs to alleviate
the symptoms. UPSHL may be the result of the treatment of Meniere’s when
the disease is causing persistent hearing loss and the vertigo attacks are
unrelenting. Injections of the ototoxic antibiotic gentamicin through the tympanic
membrane result in destroying the balance in the ear, but also can result in
further loss of hearing (Gibson, 2003).
1.4.6 Immunological
Autoimmune inner ear disease may result in a UPSHL. Types of autoimmune
diseases such as vasculitis, scleroderma and Kawasaki disease can result in
hearing loss.
1.4.7 Idiopathic
Idiopathic sudden sensorineural hearing loss can present as a UPSHL. Causes
of idiopathic sudden sensorineural hearing loss are unknown, but three common
theories are they arise from a viral infection, vascular occlusion or intra cochlear
membranous rupture. As childhood viral infections can cause a sudden
UPSHL, many individuals report these viruses as the cause of their loss.
However, unless serology for the virus has been conducted to establish the
actual cause of the hearing loss, these individuals should be classified as
having an idiopathic sudden hearing loss.
The cause of Meniere’s disease is unknown, however greater understanding of
the mechanism which triggers the symptoms of recurring attacks of vertigo,
nausea and vomiting, hearing loss, tinnitus and a blocked sensation in the
affected ear is increasing. Meniere’s disease is progressive with three distinct
stages and it is the final stage that generally causes a UPSHL in the affected
ear. This third stage is described as “burnt-out” Meniere’s in cases when the
disease is left untreated, resulting in an ear with poor balance and unusable
hearing, but is without the acute attacks of vertigo. Treatment with ototoxic
drugs for Meniere’s disease may cause a UPSHL. Similarly, the surgical
treatments of Meniere’s disease all have a risk of causing a complete hearing
loss.
21
Despite numerous possible causes for UPSHL, once damage to one side of the
hearing system has occurred in either the developing hearing system or
acquired through disease, trauma, this damage results in monaural input to the
higher cortical areas, limiting binaural processing cues. Therefore, regardless of
causality, individuals are faced with similar hearing issues as a result of their
UPSHL.
1.5 Loss of binaural hearing cues
Having hearing in two ears (binaural hearing) is critical for the brain in order to
receive and process signals from the two sources. Two ears allow the auditory
system to function and enable hearing in the dynamic world of sound. Binaural
hearing provides an increased understanding by cancellation of background
noise to enable discrimination of a particular voice from the completing noise
(Dillon, 2001). The competing background noise may comprise of three or four
different speakers or environmental noise such as music. With a unilateral
hearing loss, the person may have difficulty hearing and/or recognising sounds
and noise, particularly when the sound source is on the affected side.
Binaural hearing can be compared to binocular vision, in that both ears
contribute to the central representation of the auditory input, just as both eyes
contribute to the central representation of the visual input (Barr & Kiernan,
1988). Hearing input that is limited to one side will result in auditory deprivation,
as auditory input is limited to one cochlea and reduced stimulation along the
ipsilateral pathways to the brain. The inability to use binaural hearing could be
described as a “neglect” effect in those with unilateral hearing losses.
Therefore, there can be a permanent loss of function of the auditory centre
when it is not stimulated effectively (Fisch, 1983). Features of the stimulus,
such as the direction and distance of a sound source rely on a discrepancy in
the arrival time of the stimulus between each ear in order to be perceived. The
different inputs to the brain from the two cochleae are compared and analysed
in the superior olivary nuclei (SON) and interpreted by the auditory cortex (Barr
& Kiernan, 1988).
22
Having input from both sides of the peripheral sensory hearing system is
important as there are maturation effects as a human develops with the brain’s
processing of binaural cues. Some abilities are present at birth such as gross
localisation, but other abilities may not reach full maturity until adolescence or
beyond. Bellis (2003) has summarised components of the neuroplasticity of the
auditory system by the following table of selected auditory processes and their
developmental ages as shown in Table 1.1. There appears to be a critical
period of development where neuroplasticity in most of the auditory processing
abilities described by Bellis (2003) may have been developed by twelve years of
age. This may be seen as a cut-off point for development of some features of
binaural processing.
The social consequences of a UPSHL are often significant. Adults with
unilateral hearing loss describe an increased difficulty hearing in noise, an
inability to localise sound and problems at work due to difficulty understanding
speech. These hearing difficulties can lead to feelings of confusion,
embarrassment, helplessness and annoyance by the individual (Sargent,
Herrmann, Hollenbeak, & Bankaitis, 2001). Lack of recognition that someone is
speaking on the affected side often results in the person being left out of group
conversation or even being classified as rude or ignorant by those who do not
know of the pre-existing hearing loss. These individuals tend to change their
behaviour e.g. positioning in a group or seating position to maximise
communication cues and reduce effort. Their communication difficulties can be
explained in terms of a loss of the UPSHL causing a loss of one or a
combination of the following binaural cues: head shadow effect, loss of binaural
loudness summation, loss of binaural squelch, and loss of localisation ability
due to issues with lack of binaural redundancy, interaural time, intensity and
phase cues (McLeod et al., 2008).
23
Table 1.1
Effects of neuromaturation on selected auditory processes
Neuromaturational effects Dichotic listening
• Right-ear advantage reaches adult values by the age of 10 to 11 years
• Neuromaturational effects on REA more pronounced for linguistically loaded stimuli
• Overall performance improves until the age of 12 or 13 years Temporal
processing • Temporal resolution abilities improve until the age of 8 to 10 years
• Gap detection abilities appear to be adult-like by the age of 6 or 7 years
• Performance on temporal patterning tasks reaches adult values by approximately the age of 12 years
Binaural interaction
• Gross localisation abilities are present at birth
• Conscious perception of auditory space occurs at 4 months of age • Precision and accuracy of localisation abilities improve until
approximately the age of 5 years • MLD reaches adult values at approximately the age of 6 years
Speech-sound
discrimination
• Ability to discriminate among all phonemes in all languages of the world present at birth
• By 9 months of age, preferential responses are seen to phonemic sequences, contrasts, and prosodic patterns of the native language
• By 12 months of age, discrimination abilities are restricted to phonemic constructs that occur in native language only
• Accuracy of speech-sound discrimination improves until approximately the age of 8 years
Top-down factors
• Maturation of attention, problem-solving, memory, and related executive abilities continues through puberty and beyond
• Ongoing linguistic, cognitive, and experiential changes occur throughout the life span
REA= right ear advantage; MLD=masking level difference Note. From Assessment and management of central auditory processing disorders in the educational setting: from science to practice. (2nd ed.) p.133, T.J. Bellis, New York: Delmar Learning.
1.5.1 Head shadow effect
The terms head shadow effect or head diffraction are used to describe the
attenuation of sound as it travels from one side of the head to the other,
resulting in the individual ears detecting a different intensity of the sound
(Vermeire & Van de Heyning, 2009). This occurs as the head naturally acts as
an acoustic barrier to sound, resulting in sounds on one side reaching one ear
sooner than the other ear as well as being slightly louder on one side (Dillon,
2001). The head shadow effect is frequency dependent, with the greatest
influence on the shorter wavelengths or frequencies above 1500 Hz as shown in
Figure 1.6. The attenuation of the sound entering the opposite hearing ear can
be up to 30dB (Dillon, 2001; Hill et al., 2006). Head diffraction is important as it
24
enables increased speech intelligibility in noise when speech and noise come
from different sides of the head. This allows the brain to attend to the ear with
the better SNR, thus improving speech understanding. As the speech
consonants which are important for speech understanding are found
predominantly in the higher frequencies, the individual affected by head shadow
has degraded speech recognition, particularly in the presence of noise (Sargent
et al., 2001).
The problem is highlighted with a UPSHL as the person has only one hearing
ear. The head shadow effect can result in poor understanding of speech-in-
noise. As head diffraction is only possible if the individual can hear mid or high
frequency parts of speech, it is compromised if there is no hearing on one side,
or if residual hearing in the affected ear is limited to very low frequencies (Ching,
Incerti, Hill, & Brew, 2004).
Figure 1.6. Head shadow effect illustrating the difference that the frequency content of the signal has on reaching the contralateral ear.
Note. From (Brice, 1998)
1.5.2 Binaural summation
Binaural summation is the phenomenon whereby the sum of two equally
sensitive ears improves hearing by an average of 6dB to 10dB in perception of
loudness at comfortable listening levels (Dillon, 2001; McLeod et al., 2008;
25
Valente, 1996). The major effect of binaural summation is speech recognition
with an 18-30% advantage with binaural hearing (Bentler, 2006). Therefore, the
loss of binaural loudness summation results in an overall loss of sensitivity to
loudness of sound. As sound is heard more softly with only one hearing ear
compared to two normal hearing ears, this may explain why individuals with a
UPSHL may require a louder than normal volume for television, or have difficulty
hearing softer voices over distance.
1.5.3 Binaural squelch
Binaural squelch or binaural release from masking is the phenomenon that
allows the brain to separate noise and speech due to differences in interaural
timing cues between the two signals (Dillon, 2001; Vermeire & Van de Heyning,
2009). Studies by Carhart (1965), cited in (McLeod et al., 2008; Valente, 1996)
reported that the loss of binaural squelch can lead to decreased speech
understanding by an equivalent 3dB in SNR because the interference of noise
and reverberation is not as effectively eliminated. In the individual with UPSHL,
not having the advantage of binaural squelch leads to having to position the
target sound source carefully. Unwanted noise can be directed to their affected
ear allowing the non-affected ear to detect the wanted speech. This however is
not possible if the unwanted noise source or target speech is moving or when
the person with a UPSHL is positioned with the unwanted noise going directly
into their non-affected ear, such as having a passenger in a car on the affected
side.
1.5.4 Binaural redundancy
Binaural redundancy refers to the advantage of hearing with identical signals
arriving at both ears. Speech perception can be improved due to the
redundancy of the signals received by the two ears. In the case of the same
signal and noise reaching both ears, the brain can combine both inputs and
increase salient central representations of the speech signal as opposed to if
input from only one ear is available (Ching et al., 2004). Without this binaural
processing skill, individuals with a UPSHL reported that they found conversation
very confusing in situations where there was competing noise. Often their
residual hearing is not adequate to enable ease of conversation in settings with
26
high ambient background noise levels such as in restaurants, at group meetings
and at parties.
1.5.5 Localising sound
The ability to localise sound and adjust head angle requires binaural hearing
due to the interaural time and intensity differences between the two ears,
particularly when listening in a noisy environment (McLeod et al., 2008). With
sound input from two sides, the brain has a better representation of speech and
noise, and is better able to locate the origin of the sound (Dillon, 2001).
Differences in the sound’s time, intensity, phase, and arrival time in reaching the
two ears enables the central auditory nervous system to accurately locate which
side the sound originates on a horizontal plane. These differences rely on the
higher levels of the brain to interpret low frequency information (Byrne, Noble, &
LePage, 1992; Sargent et al., 2001).
Individuals with normal hearing have an overall awareness, or a three-
dimensional representation of sound that is innate. Three-dimensional hearing
allows the individual to have a psychological advantage or emotional well-being
that they are aware of sound surrounding them. An individual with a UPSHL
does not have this spatial awareness and is unable to localise sound,
particularly on the horizontal plane. They may feel that their safety is
compromised as due to their poor localisation skills. They are likely to miss
critical auditory cues that allow them to hear incidental warning sounds, for
example hearing a person or a cyclist on a dual use pathway is approaching
them on their “deaf” side from behind, and the direction of approaching vehicles.
With no ability to localise sound, the individual has to scan the environment to
visually obtain the source of the sound. This results in a slower response time
in recognising and locating the sound source. They rely on positioning people
on their “good” hearing side when walking beside them. Overall impaired
localisation may result in reduced safety and difficulties in social functioning
(Ching et al., 2004).
27
1.6 Studies on unilateral hearing loss
As previously discussed, the fundamental problems reported by people with a
UPSHL are not being able to hear on their deaf side, hearing clearly over
distance, hearing in crowded, noisy situations, and/or detecting where sound is
located. These problems relate to the individual’s poor speech recognition
ability in noise and reduced localisation skills. The impact of binaural hearing
loss is significant, while the presence of a UPSHL are not immediately obvious
to the individual’s communication partner, as the individual can still hear well
with one ear (Sargent et al., 2001). Children with a unilateral hearing loss are
typically diagnosed later than bilaterally hearing impaired children as parents
observe inconsistent behaviour to sound; and/or miss the subtle cues indicating
a hearing loss (Bess, Rothpletz, & Dodd-Murphy, 2002), although the age of
diagnosis of unilaterally hearing impaired children is becoming earlier with
increased neonatal screening and better diagnostic testing of younger infants.
Some individuals cope relatively well with a UPSHL as they have well-
developed coping strategies for difficult listening situations. However, others
may report a multitude of difficulties, including speech understanding in noisy
situations (Hill et al., 2006).
The significance of an acquired unilateral hearing impairment was investigated
by Feuerstein (1992), who simulated unilateral hearing loss in normal hearing
subjects. The subjects’ performance in word recognition, attentional effort,
speech tasks in noise, and ease of listening ratings were evaluated. Feruerstein
found that listening ratings and word recognition were easier if binaural cues
were available to the individual. Perceived quality of sound was also reported to
be an issue when there was an absence of binaural hearing (Perez, Rodriguez,
Macias, & Garcia-Ibanez, 2004).
Ponton et al. (2001) in their study of brain plasticity in subjects with late-onset
profound unilateral deafness suggested that with auditory evoked potential data,
the cortical activity changes were gradual and that they continue for at least two
years after the onset of hearing loss. They surmised that these changes
indicated neural plasticity. This has also been well documented in cochlear
implant studies that recipients are able to adapt and utilise new sound through
28
their implant(s). There have been studies indicating an increase in activation
along the ipsilateral auditory pathways on the intact hearing ear side in unilateral
hearing-impaired individuals. Ponton et al. (2001) reported that contralateral
auditory pathways are stronger than ipsilateral ones in normal hearing subjects.
Studies of adults with a congenital unilateral impairment have shown that these
subjects are able to localise better than normal hearing subjects who had been
given a pseudo unilateral hearing loss (Stattery & Middlebrooks, 1994).
A retrospective study of twenty-one subjects with unilateral sudden
sensorineural hearing loss and its associated audiological handicap, reported
that 86% of the subjects reported having a hearing handicap; with one in ten
subjects experiencing a severe audiological handicap (Chiossoine-Kerdel,
Baguley, Stoddart, & Moffat, 2000). Colletti et al. (1988) compared the long-
term effects of unilateral hearing loss in forty adults who had been diagnosed
with their loss in early childhood to a control group of forty-five individuals with
normal hearing, matched for gender and age. The criteria for the unilateral
hearing impaired subject group was a hearing level worse than 40 dB HL that
was acquired before school age, and the absence of any other significant
general or neurological disorder. The study involved administering a
questionnaire designed by the researchers aimed at identifying objective and
subjective indices of psychosocial disability and handicap. There were sections
relating directly to auditory function, degree of education, type of employment as
well as social interactions with family, friends, work colleagues, finance,
housing, and social/leisure activities
The significant differences between the two groups were in the following
situations: listening to or playing music as a hobby, difficulties in speech
recognition in noise; and sound localisation, with the hearing impaired group
reporting their percentage of difficulty to these two situations being 95% and
82.5%, respectively (Colletti et al., 1988). The researchers did find that the
unilateral hearing impaired group had reduced difficulties with telephone
conversation in the presence of noise, when compared to the group with normal
hearing. By using their better hearing ear on the telephone, these individuals
would have less interference from background noise due to the ability to tightly
29
couple the phone around the hearing ear effectively masking out the noise. The
group of hearing subjects would be dealing with the two auditory inputs,
therefore needing to obtain a better SNR on the side of the telephone to hear
effectively. Overall the researchers concluded that long-term unilateral hearing
impaired subjects were not affected by the lack of auditory function in both ears
as they coped well in the psychosocial aspects such as education levels,
employment and social problems that were explored in the questionnaires, but
acknowledged the reporting of specific difficulties by this subject group with
particular listening situations was due to the lack of binaural hearing.
1.7 Quality of life aspects and outcome measures
To evaluate the impact that hearing loss has on an individual’s lifestyle, there
are many outcome measures in the form of questionnaires that can be
administered by audiologists. Self-reported measures of outcome are used to
enable the audiologist to determine the real-world benefits that the individual
has received from the hearing aid performance, as objective measuring is
generally for research purposes or performed in a clinical setting that are
artificial to real life situations.
Outcome measures can be used to examine if the individual has limitations in
activities and participation restrictions in day to day interactions (Abrams, 2000).
Each type of hearing loss has its unique issues, which are specific to that
particular individual. Therefore, it is important to establish what are the
particular problems the individual is experiencing prior to and following
intervention. For example, those with conductive hearing losses usually require
greater medical follow-up than those individuals with sensorineural hearing
losses. Conversely, conductive hearing losses may require less time for
adjustments to amplification devices than sensorineural hearing losses. The
issue of a UPSHL is different to other types of hearing losses as only one ear is
affected and the degree of the hearing loss limits rehabilitation strategies.
There is currently no specific validated questionnaire that has been designed for
individuals with a UPSHL to assess the individual’s specific problems pre-and
post-intervention. There have been some questionnaires designed in-house by
clinics or researchers for this particular hearing impaired population that have
30
had their results published, but there has been no standardisation for validation
or reliability studies of these questionnaires (McLeod et al., 2008).
Outcome measures have been used in previous studies to demonstrate
accountability of treatment, validating clinical decisions to continuously and
effectively improve care, and establishing and maintaining “best practices”
(Abrams, 2000). Outcome measures are designed to assess change in the
individual’s health status resulting from treatment. Robinson, Gatehouse &
Browning (1996) reported that measurements of benefit resulting from
intervention should be patient-orientated, be sensitive to health status following
intervention and be able to make comparisons between different interventions.
Patient-orientated measurement provides systems that can be used in research
to determine the relationship between patient benefit and pre-intervention
variables such as personality, motivation and expectations (Robinson, et al,
1996).
Health-related quality of life (HRQOL) evaluations can be generic or disease-
specific to help determine the benefit of medical treatment. Generic measures
enable the comparison between individuals with different conditions as well as
comparisons to the general population. However, generic measures have been
found to have limited value in evaluating subjects with hearing impairment
following intervention with amplification devices as they are not sensitive to the
changes that occur with communication issues as they are not examined (Mo,
Harris, & Lindbaek, 2004; Snik et al., 2005).
Hol, Spath, Krabbe & van de Pouw (2004) found that in their study of 56
subjects who were fitted with BAHA for traditional otolaryngological reasons
following previous use of conventional air and bone conduction devices, there
were significant benefits in fitting of BAHA. They administered two generic
measures, being the Medical Outcomes Study short form SF-36 Health Survey
(SF-36) and Euro Quality of Life-5D (EQ-5D) global survey.
These questionnaires were administered before the BAHA surgery and six
months post-operatively. The total subjects’ group scores from the SF-36
31
showed the only one difference between the pre-and post-surgery mental health
domain scores. There were no important differences shown between pre- and
post-surgery in the EQ-5D scores. The subject group as a whole showed
slightly poorer scores on mobility, pain/discomfort and anxiety/depression
domains after implantation. However, the disease-specific measure, Hearing
Handicap Inventory (HHDI) for Adults scores showed a significant improvement
in both the disability and handicap scales with the same subjects associated
with implantation. The results were independent of previous hearing aid use. In
the hearing aid related questions; all of the subjects were wearing their BAHA
device eight or more hours each day. The subjects reported a reduced number
of visits to otolaryngologist for complaints about draining ears. Hol et al.
(2004b) argued that generic measures were not representing the actual impact
on subjects' well being as they did not show BAHA treatment effects after six
months of use, despite the disease-specific questionnaire, the HHDI, as well as
objective testing showing BAHA benefit.
Another study of eight BAHA subjects implanted for UPSHL used both generic
and disease-specific measures of QOL. The researchers found that the generic
measure (SF-36) was unable to show any significant benefit to the fitting of a
BAHA while the disease-specific HRQOL survey, Hearing Handicap Inventory
for Adults (HHIA) did show significant differences (Newman, Sandridge, &
Wodzisz, 2008).
Abrams (2000) argued that general health status instruments lack specificity to
hearing aid benefit due to absence of questions relating to hearing function and
its impact on communication. He reports that disease-specific outcome
measures provide a better symptom score associated with the disease. These
scores are then used as an outcome measure by comparing the change in
status following intervention (Robinson et al., 1996). Disease-specific outcome
measures can be used to evaluate the same health condition with different
treatments (Abrams, 2000). Hol et al. (2004b) reported the Glasgow Benefit
Inventory (GBI, Robinson et al., 1996) was one of the only validated, generic,
health related quality of life (QOL) inventories that was patient-orientated for
hearing impairment. They suggested that the questionnaire is designed for
32
measuring outcomes of the patient’s benefit and not health status per se
following otorhinolaryngological intervention. These retrospective studies found
significant improvement in patient’s QOL after BAHA surgery, an improvement
comparable to results obtained in middle ear surgery. Shanker et al. (2004)
found that when assessing a small number of individuals post-BAHA fitting for
UPSHL as a result of acoustic neuroma removal and mastoidectomy. They
measured a higher rating of benefit using the GBI, than the average of all the
other BAHA users, and similar to other studies of GBI and the reported benefit
following cochlear implantation.
In addition to HRQOL surveys, disease-specific questionnaires have been used
to examine the domains for hearing with regard to sound quality, comfort,
cosmetic appearance, practical arrangement and utilisation time (amount of time
worn). Another area that can be evaluated is user satisfaction which differs
from benefit as it is not performance driven (Taylor, 2007). The use of several
outcome measures can help identify trends (Abrams, 2000).
The main disease-specific questionnaires that have been used in studies to
examine the subjective benefit of the surgical intervention and fitting a BAHA to
UPSHL are the Abbreviated Profile of Hearing Aid Benefit (APHAB), Glasgow
Hearing Aid Benefit Profile (GHABP) and the Entific Single Sided Deafness
Questionnaire (SSDQ).
1.7.1 Abbreviated Profile of Hearing Aid Benefit (APHAB)
The Abbreviated Profile of Hearing Aid Benefit (APHAB- Version A, Cox &
Alexander (1995) is a standardised 24 item self-assessment inventory in which
the subject reports the degree of difficulty they have with communication and
perception of environmental sounds. The questionnaire’s outcomes are divided
into four subscales: ease of communication (EC scale), background noise (BN
scale), reverberation (RV scale), and aversiveness (AV scale). The subscales
EC, BN and RV are used to look at speech understanding in everyday
situations. The AV scale looks at negative reactions to environmental sounds.
The percentage scores show how frequently the subjects experienced
problems. The questionnaire indicates clinically significant benefit with 90%
33
level of certainty when the subject’s mean aided scores exceed the mean
unaided scores by 5% for each of the speech communication subscales (BN,
RV and EC) to give a global assessment. The subscale AV is not included as
part of this global assessment (Cox, 1997).
One of the disadvantages of this questionnaire is that due to its standardisation,
some of the questions may not be relevant to the subject and therefore the
results may not be as sensitive to benefit of intervention (Abrams, 2000).
Another issue is that responses are arbitrarily descriptive, such as “seldom”,
“occasionally’ which could mean many things to different individuals. The use of
the corresponding numerical representation in the form of a percentage, may be
argued to counter balance this ambiguity. There are also reversals in the
scaling direction, which although not uncommon in many surveys may cause
confusion in some respondents. Cox (1996) argues that it ensures the subject
is reading each question and paying close attention to the questionnaire. Cox,
however, does acknowledge that elderly subjects in particular may find the
inventory confusing, although reports that the inventory should be administered
in an interview style which may resolve this issue.
1.7.2 Glasgow Hearing Aid Benefit Profile (GHABP)
The second questionnaire administered to subjects was the GHABP
(Gatehouse, 1999). This questionnaire can be administrated as one or divided
into two separate questionnaires to differentiate pre-fitting (unaided) and post-
fitting (aided) responses. In this study, this questionnaire was administered as
two separate questionnaires. The second version of the questionnaire the post-
fitting questionnaire - is based upon the subjects’ responses to the first version.
This questionnaire wording refers to the device fitted as a hearing aid; and as
the BAHA is an implanted hearing aid, none of the wording had to be altered to
suit the subject group in this study. The questionnaire outcomes contain
subsets that give scores for initial disability, handicap, hearing aid use, benefit,
residual disability and satisfaction. The benefit of the GHABP is that it combines
both standardised questions as well as subject goal-orientated areas for
intervention. It has four set questions that the subject responds to, but also
allows the subject to nominate up to four areas of hearing difficulty. The
34
responses to both standardised and nominated listening situations are
compared to the subjects’ aided outcomes. The questionnaire was designed to
determine the success of an intervention and evaluate whether further support
or intervention is required (Medical Research Council, Institute for Hearing
Research, 2005).
One disadvantage of this style of open-ended questioning, with the individual
being able to nominate specific hearing difficulties, is that there is no prescribed
method in the administration to rate the hearing difficulties with a hierarchy of
most to least significant importance to the individual. Therefore, not having a
hierarchy of hearing goals does not reflect the most important hearing difficulties
to be evaluated in rating the success of intervention. Another questionnaire, the
Client Orientated Scale of Improvement (COSI) (Dillon, James, & Ginis, 1997)
also has open-ended questioning allowing individuals to identify, state and rank
five areas of communication difficulties due to hearing loss. This allows a
rehabilitation to be tailored for the individual, but being so open-ended it can be
difficult for many individuals to verbalise difficulties precisely to create outcome
goals for the intervention program. However, despite specific rating of the
nominated hearing difficulties not being part of the GHABP, as the questionnaire
was part of an interview in the initial assessment, the particular areas of concern
could be determined. Therefore, the greatest benefit of the GHABP is that it
combines both standardised questions as well as individualised goal-oriented
areas for intervention.
1.7.3 Single Sided Deafness Questionnaire (SSDQ)
The SSDQ (Entific Medical Systems AB, Goteborg, Sweden) was specifically
designed to be administered after BAHA implantation for UPSHL. The use of
this questionnaire was first detailed in study by Wazen et. al (2003). This is a
user-friendly questionnaire, with questions relating to UPSHL hearing difficulties,
usage and satisfaction of wearing a BAHA for UPSHL. It was based on the
questionnaire developed by Entific Medical Systems (2001), published in their
audiology manual to administer to general BAHA recipients.
35
The SSDQ has greater specificity for UPSHL with treatment of BAHA as this
was designed to be administrated post-operatively to individuals who have
received a BAHA for UPSHL. The other two questionnaires can be used
generically with any type of hearing loss, with pre- and post-intervention of any
hearing rehabilitation method. One disadvantage with the SSDQ is that it is a
subject satisfaction questionnaire, so that results are always affected by a
positive bias, particularly as subjects feel grateful for intervention even if it is not
technically successful (Robinson et al., 1996).
Both the GHABP and SSDQ focus on subject satisfaction with their device. The
satisfaction domain examines whether the device meets or exceeds the
expectations of the individual, but also reflects the individual’s perception of the
complete audiological service (Abrams, 2000). The SSDQ reaches some of
these goals by examining the positive effects, negative features and personal
image (cosmetics) of the BAHA device.
Questionnaires not only formulate the basis of outcome measures, but also
allow the hearing professional to recognise the particular difficulties that the
individual has in regard to their hearing in certain listening situations. The
responses of initial questionnaires can be used to design communication goals
in the areas of hearing difficulty to be addressed, and can be a guide to the form
of intervention that is most appropriate for that individual.
1.8 Summary
When examining the literature on the effects due to lack of binaural cues, the
hearing difficulties that individuals with UPSHL report are similar to studies of
other hearing impaired groups, such as unilateral cochlear implant users. As
the individual with a UPSHL has normal hearing in one ear, this may have been
lead to the communication difficulties of this hearing impaired group being
underestimated in the past. However, more research is showing the extent of
the effect of the UPSHL on the individuals’ quality of life.
For those individuals who acquire a UPSHL, the impact of the hearing loss on
their lifestyle can be significant. Stahl & Cohen (2006) reported that their
36
subjects who had normal hearing, then a sudden unilateral hearing loss,
commented on the loss of localisation of sound, and the psychologically
disturbing or overwhelming impact of tinnitus where it was associated with the
loss of hearing. Whether the subject obtains intervention is strongly dependent
on the time of the hearing loss onset. If the cause is VS, the individual is usually
an adult. The individual may experience a sudden UPSHL following surgery to
remove the VS. In this case, the individual may seek rehabilitation sooner than
someone whose hearing loss has gradually progressed to the profound level.
Their case is similar to those who present with an idiopathic sudden
sensorineural hearing loss.
Fifty percent of individuals with a sudden hearing loss will not have recovery in
their hearing, with most seeking help as a result of their permanent UPSHL
(Stahl & Cohen, 2006). Individuals with a UPSHL may obtain intervention for
many reasons. Intervention is particularly significant for those individuals whose
hearing has once been within normal hearing thresholds, as the UPSHL may
result in a change to their pattern of communication and socialisation (Peters,
2007). On the other hand, the individual who has a congenital UPSHL may see
their hearing status as “normal” because they have only ever heard in one ear.
Such an individual may not obtain any intervention at all.
37
Chapter 2: Traditional options for UPSHL
There are a significant number of individuals with UPSHL. Therefore,
professionals with an interest in such losses, such as audiologists,
otolaryngologists and hearing aid manufacturers alike, have explored several
interventions to help overcome the communication difficulties that those with a
UPSHL experience. To date, all rehabilitation strategies for a UPSHL, except
one, have involved directing sound from the poorer hearing ear to the better ear.
The exception is the use of a conventional cochlear implant in the affected ear.
However, this strategy is still undergoing preliminary research and is limited to a
particular subject cohort of individuals with incapacitating unilateral tinnitus.
2.1 Transcranial hearing aids
Transcranial hearing aids or “transcranial CROS devices” have been used to
treat UPSHL for many decades with mixed success. Transcranial sound
transmission can be achieved with various types of conventional air conduction
hearing aids (ACHAs). Either a powerful behind-the-ear (BTE) hearing aid (Snik
et al., 2005), a high output in-the-ear (ITE) hearing aid (Hill et al., 2006), or a
completely-in-the-canal (CIC) hearing aid (Hayes & Chen, 1998) can be placed
in the affected ear.
A transcranial CROS fitting uses the physical vibrations of the hearing aid’s
receiver components to activate bone conduction as a method of sound
transmission to the other hearing cochlea (Hayes & Chen, 1998; Snik et al.,
2005). For a transcranial hearing aid to be effective, part of the device must lie
within the bony portion of the ear canal to enable vibration for transmission.
This can be uncomfortable for some individuals, as this part of the ear canal is
highly sensitive with little tolerance for pressure, any device imperfection, or
expansion with heat of the device (Australian Hearing, 1997).
The osseous structure of the ear canal is part of the tempo-mandibular joint.
Individuals with unusual tempo-mandibular joint movement will be sensitive to
discomfort. Such movement can also trigger acoustic feedback from the
38
hearing device. There may also be medical contraindications to making the
deep ear canal impressions required to fit a transcranial hearing aid. For
example, conditions resulting in abnormalities in the ear canal (e.g. exostoses,
which are benign bony growths), previous ear surgery, dermatitis or chronic ear
infections, abnormally shaped canals, severe bends within the canal, or small
restricted ear canals can all be contraindications for the fitting of deep-seated
hearing aid devices. Other factors, which have limited the success of wearing a
conventional hearing aid in the affected ear, include acoustic feedback and
inability to obtain adequate volume from the aid to enable effective bone
conduction transmission across the skull to the other cochlea.
2.2 Contralateral routing of signal (CROS) hearing aids
A CROS hearing aid consists of two parts: a microphone which is worn on the
affected ear (usually encased in a hearing aid), and a second hearing aid which
is worn on the non-affected ear and captures sound from the remote
microphone and directs sound into the ear canal of the non-affected ear. This
allows the listener to hear sound coming from the affected side but does not
improve localisation ability (Australian Hearing, 1997). CROS aids are either
hard-wired or wireless through radio frequency transmission. Hard-wired
devices have a cord connecting the two parts that runs along the nape of the
neck as shown in Figure 2.1.
39
Figure 2.1. Photograph of a hard wired PIC 2 CROS aid system with a remote control.
Note. From (Valente, Valente, & Mispagel, 2006)
Newer to the market are the wireless CROS systems (e.g. the wireless WiFi Mic
manufactured by Unitron Hearing, released in 2005), whereby the signal from
the microphone on the deaf ear is sent to the receiver worn on the good ear via
frequency modulation (FM) signals as shown in Figure 2.2. Therefore, the two
components of the system are linked, but the need for a cord as used in the
traditional CROS set-up is eliminated.
Figure 2.2. WiFi Mic with behind-the-ear hearing aid system.
NB: External casing and internal components with receiver. The blue arrow indicates the transfer of the frequency modulated (FM) signal on the left device in both diagrams.
Note. From (Unitron Hearing Ltd, 2007)
40
The limitations of CROS aids are well documented, and the difficulty in fitting the
group with UPSHL has been evaluated by many researchers (Hill et al., 2006;
Niparko et al., 2003; Wazen et al., 2003). One of the manufacturers of the
wireless CROS systems (Telex Communication Inc, Minneapolis MN) stated
that radio signal is subject to electrical interference and is one of the limitations
of the wireless CROS device. Another disadvantage of CROS aids is that a
device must be worn in each ear.
Byrne, Noble & Sinclair (1996) found that when people were aided with a closed
ear mould, it could impair their ability to localise on the horizontal plane. They
concluded that the reason for this was related to distortion of the interaural
phase and time differences between ears.
When individuals wear hearing aids their natural bone conduction (BC) is
altered. This results in the phenomenon called the “occlusion effect”. It is
caused by an interruption of the temporomandibular joint, which results in the
lower jaw vibrating out of phase with the remainder of the skull bones. This
causes displacement in the vibratory rate of the cartilaginous skeleton of the ear
canal, causing a sensation of increased loudness (Zemlin, 1988). In normal
non-occluded ear individuals normally hear themselves through a combination
of air and bone conduction. When a hearing aid is worn, the moulding of the
hearing aid in the ear canal changes the natural resonance and bone
conduction sound. Occlusion results in a perceived distortion to the sound of an
individual’s own voice, often described by the individual as making their voice or
speech sound “echoey”, “hollow” and/or “boomy”. The bone conducted sound
provides a biofeedback channel for voice monitoring (Zemlin, 1988), so these
individuals find wearing the hearing aid distracting and disturbing as their voice
does not sound “natural”.
Therefore, the occlusion effect has been reported as a major disadvantage for
users of CROS hearing aids, whether it is wired or wireless, and it may be a
contributing factor as to why individuals have rejected the use of these devices
in the past. Although open or minimal moulding has improved the reported
41
occlusion, individuals with UPSHL still report this physical sensation despite the
less invasive mould in their non-affected ear.
Valente (1996) asserted that CROS aids can reduce the release of masking
signals from the good side if gain of the device is incorrect. The head shadow
effect can be counteracted if the noise level input into the microphone on the
affected side overpowers the input from the good ear. Other disadvantages of
these systems have been the inconvenience of wearing a two-part device, the
limitation of subjective gain and their cost (Welsh, Welsh, Rosen, & Dragonette,
2004).
CROS devices have been reported to have minimal benefit in assisting with the
understanding of speech-in-noise; small benefits hearing speech over distance
as they do not restore the binaural summation or squelch effect, or improve
localisation. They do overcome the head shadow effect (Australian Hearing,
2008b; Hill et al., 2006; Sargent et al., 2001). Therefore, CROS aids are
typically used to assist with the following communication difficulties: hearing in a
car or airplane if the affected ear is closest to the person speaking (a fixed
seating arrangement); improving safety in a work situation; and hearing the
television or radio at a normal volume. However, there are a small group of
subjects who embrace this system and use it successfully in both work and
social environments involving situations with significant amounts of noise. The
major benefit of a traditional CROS system is that the device is non-invasive so
the individual does not require surgery. This is particularly significant for those
individuals who have acquired their UPSHL due to surgical excision of their VS
and do not want to undertake further surgery.
The CROS aid may also be an option for an individual with UPSHL, whose
hearing in the non-affected ear deteriorates over time due to the ageing effect,
or suddenly changes. Studies have found that the CROS to be particularly
useful for people with a mild high frequency hearing loss in the better hearing
ear (above 1500Hz), and if the user varies their head position in order to
partially determine which direction the sound is coming from (Valente, 1996).
42
Welsh et al. (2004) conducted a study of the speech-in-noise ability of three
groups. One group had twenty subjects with a high frequency sensorineural
hearing loss (≥2kHz) in the better hearing ear and profound deafness in the
other ear. Another group of nineteen subjects had hearing with normal limits,
and the third group of sixteen subjects had a UPSHL. They found that subjects
with the high frequency SNHL in the better ear had a poorer performance when
testing speech-in-noise than the group of subjects with a UPSHL and the normal
hearing group. They attributed this decrease in performance to the attenuation
of frequencies above 2kHz in the opposite ear, which had affected the speech
discrimination ability. If this is the case, appropriate amplification is warranted
for these individuals with a UPSHL and a high frequency hearing loss in the
opposite ear.
2.3 Frequency modulated (FM) systems
Personal wireless FM systems are available for individuals with all types of
hearing loss. An FM system consists of two parts: a transmitter and a receiver
as shown in Figure 2.3. The signal from the microphone, generally worn by the
target speaker, is transmitted to the individual’s receiver via FM radio wave. In
Australia, children with a unilateral hearing loss may be fitted with a Phonic Ear
FM system or an EduLink system via the government provider Australian
Hearing (Australian Hearing, 2008b).
Figure 2.3. Edulink FM receiver and a Smartlink Transmitter
Note. From (Phonak Limited, 2009).
The major advantages of FM systems are that they reduce the adverse effects
of distance, noise and reverberation within the listening environment. They can
improve the SNR as the target voice can be amplified without amplification of
the background noise. Australian Hearing (2008b) reported that personal FM
systems are beneficial in assisting individuals to understand speech-in-noise, for
43
hearing speech over distance, and hearing on the affected side if the speaker is
situated on that particular side.
FM systems were traditionally designed to be used in conjunction with a hearing
aid. However, the Phonic Ear FM system uses an ear-bud or headphones to
direct the sound into the non-affected ear. The EduLink S is an FM system
designed by Phonak Hearing Systems that can be fitted to children and adults
with a unilateral hearing loss. It is a multi-frequency FM receiver that allows the
speech via the transmitter to be up to 20 decibels louder than the background
environmental noise. The Edulink S can be used with all the Phonak
transmitters and allows the speaker’s voice to be directly channelled into the
non-affected ear via a specially designed earphone connected to the FM
receiver. Adults can be assisted by FM systems with desk-attached units
(Welsh et al., 2004). Some individuals use their FM system to help hear the
television at a volume acceptable to other family members who have normal
hearing (Australian Hearing, 2008b).
The disadvantages of FM systems are that the individual has to explain the
equipment to his/her communication partners, and they have to carry the
devices to use in difficult listening situations, which can be noticeable to others.
The FM system does not overcome the issue of localisation, as the sound is
directed into the non-affected ear.
2.4 Monitoring hearing loss
The conservative approach to managing an individual with UPSHL is to monitor
the hearing in the non-affected ear. Cases of unilateral hearing loss in children
have not been considered significant in regards to management. Children born
with a unilateral hearing loss were not traditionally offered much assistance as it
was considered that normal hearing in one ear was enough for normal speech
and language development as well as academic performance. However,
despite having developed strategies to compensate for their hearing loss, these
children still have difficulty in the school environment, particularly in group
activities.
44
Bess & Tharpe (1986) reported that 35% of children with permanent unilateral
hearing loss fail one or two grades at school. Culbertson & Gilbert (1986)
reported that in their study of twenty-five unilateral hearing impaired children
with matched controls with normal hearing, that the hearing impaired group had
lower scores on academic testing of word recognition, spelling and language,
despite no significant difference to the control group on self-concept and
cognitive measures. They highlighted the difference in the severity of the
unilateral hearing loss, with those children with severe to profound unilateral
losses having greater verbally based learning difficulties.
The unilateral hearing impaired children were rated by their teachers as having
less social confidence, greater difficulty in peer relationships, and were more
frequently distracted than their peers. These children present with the same
myriad of problems that adults with a UPSHL report. However, with children,
the parents generally heed the advice of the hearing professional whether to
monitor or obtain intervention. Therefore, careful counselling and monitoring of
education outcomes is important with these children if they do not proceed with
any form of intervention.
If monitoring is the preferred option of the individual, they are usually advised of
hearing tactics such as preferential seating placement, minimising background
noise, speaking with small rather than large groups of people, and placement of
the functional ear in the direction of the sound source. The limitations of this
treatment option are that not all environments are the same and able to be
manipulated. Social or work commitments do not always allow for a smaller
group situation and minimal background noise environments for these
individuals.
Individuals with UPSHL have been a neglected hearing impaired group due to
the limited technology available to them. Previously, it was also mistakenly
thought that one working cochlea would be sufficient for hearing in all listening
situations. In the past, the individual’s hearing in the non-affected ear was
usually monitored and intervention via amplification did not occur until this
hearing became compromised by either noise or age related hearing loss
45
(presbycusis), or by trauma or disease. Monitoring of hearing may also occur in
some cases of VS, despite the tumour being detected medically. Repeated
MRIs may show that the growth of the tumour is slow, therefore may be judged
to be manageable and have minimal impact on the life of the individual, and so
the hearing is monitored.
Careful counselling about hearing protection in the better ear should be part of
the management of all subjects with a UPSHL (Chiossoine-Kerdel et al., 2000).
Those individuals who have a long-standing UPSHL find that a sudden hearing
loss of hearing to the other ear is traumatic as it instantly impacts the individual,
reducing their already compromised hearing system of reliance on monaural
cues.
46
Chapter 3: The bone anchored hearing aid (BAHA)
3.1 Background information on the BAHA
The BAHA was first proposed in 1977, as a device consisting of titanium
implants inserted into the temporal bone for the treatment of conductive hearing
losses (Tjellstrom, 2008). The BAHA product was first commercially released in
1985 (Macnamara, Phillips, & Proops, 1996).
3.1.1 Surgical procedure
The surgical procedure for the BAHA system was described by Anders
Tjellstrom over twenty years ago for the treatment of hearing loss (Snik et al.,
2005). The surgical techniques and tools have evolved over the tens of
thousands of BAHA surgical procedures with the introduction of a self-tapping
implant in 2001 and the dermatome tool to create skin grafts. Although the
surgical technique used will depend upon the surgeon, the manufacturer has
developed surgical guidelines in order to enhance and optimise the best surgical
outcomes for the individual. The BAHA surgery is reversible and low risk
(Stenfelt, Hakansson, Jonsson, & Granstrom, 2000; Tjellstrom & Hakansson,
1995). The BAHA system works through direct bone conduction whereby sound
is conducted through a percutaneous abutment to the bone, by-passing hair,
skin and subcutaneous tissue on the mastoid region of the temporal bone. The
BAHA has three main components: an internal titanium implant, an abutment
and an external sound processor as shown in Figure 3.1 and Figure 3.2.
47
Figure 3.1. Diagram of three components of the BAHA system.
NB: Figure shows the titanium implant, the abutment and external sound processor of the Compact model.
Note. From (Entific Medical Systems, 2005c).
Figure 3.2. Diagram of a placement of the BAHA in the mastoid region of the temporal bone.
Note. From (Entific Medical Systems, 2005d).
The titanium screw is placed into the temporal bone behind the ear and a skin-
penetrating abutment is generally installed in a one-stage surgical procedure in
adults. Surgery can be performed under general or local anaesthesia
(Macnamara et al., 1996; Snik et al., 2005). A two-stage procedure is typically
used for the paediatric population or adults with poor bone quality or depth as
shown in Figure 3.3.
48
Figure 3.3. Diagram detailing the titanium screw within the mastoid bone.
NB: This diagram illustrates the a two-stage procedure of how the implant is inserted with a skin flap being sutured over the top of the implant.
Note. From (Entific Medical Systems, 2005d).
Surgery involves a template being used to position the implant behind the pinna,
superior to the external auditory canal. Initially, surgery was performed creating
a U-shaped incision manually with a scalpel. Removal of hair follicles and
thinning in the flap of skin in which the abutment penetrates is part of this
procedure. This produces a split thickness skin graft (Macnamara et al., 1996).
This manually created graft can be a full thickness skin graft or a split thickness
skin graft, the difference being how thick the final skin graft is. Due to issues
with post-surgery soft tissue reactions, a specially designed skin grafting tool
called a dermatome was developed to create a thinner skin site around the
abutment.
Current surgical practice is to use the dermatome, which creates a superiorly
based skin graft. The dermatome has also reduced the need to manually
remove hair follicles from the skin flap, as the thinness of the skin graft created
by the tool does not contain hair follicles; they lie in a deeper dermis layer.
However, some surgeons prefer to manually scrap the underside of the graft to
ensure no hair follicles remain (Stalfors & Tjellstrom, 2008). Soft tissue
surrounding the site for the abutment is reduced to the level of the periosteum
which adheres to the bone (Weber, 2002).
49
Once the excess subcutaneous tissue has been surgically removed, the implant
is drilled into the bone with a self-tapping implant (Stalfors & Tjellstrom, 2008).
With the abutment in place, the skin graft that has been created is punched to
allow the graft to expose the percutaneous titanium abutment and is skin flap is
sutured into place. Part of the post-operative care protocol is the placement of a
healing cap over a dressing such as a piece of xeroform gauze (petroleum-
embedded gauze) positioned around the abutment (Entific Medical Systems,
2001; Falcone & Labadie, 2007). The healing cap and dressing are designed to
apply pressure around the abutment to keep the skin as flat as possible. The
healing cap is removed one week post-surgery (Weber, 2002), after which the
wound is redressed and the healing cap replaced. One week later, the healing
cap is removed.
Falcone & Labadie (2007) reported an alternative to the manufacturer provided
healing cap. They used a bolster dressing and found that in twenty-three
subjects who had this alternative post-surgical dressing, there was 100% split
thickness skin graft survival compared to 71% skin graft survival with the healing
cap group of seven subjects. They reported that the bolster dressing stabilised
the skin surrounding the abutment, whilst the healing cap can rotate while
affixed to the abutment. They noted that due to this mobility the subjects are
restricted in their post-operative activities as they must treat the healing cap with
care to minimise its manipulation. Showering and washing hair is restricted with
a healing cap until after the first 48 hours post-surgery, whilst the bolster
dressing, allows showering immediately post-surgery (Falcone & Labadie,
2007). During the initial post-surgery period, the individual has to keep the
abutment site clean and dry. After surgery most individuals can resume their
normal daily activities around one week after surgery. No strenuous exercise or
contact sport is recommended in the immediate post-surgery period.
Over time, the surgically placed titanium implant naturally integrates with the
skull bone via a process called osseointegration. This term was first used by
Branemark in 1952 to describe the process of titanium oxide permanently fusing
with bone with a direct structural and functional connection. Initially used in
dentistry for fixtures in teeth, it is used for cranial and maxillofacial fixtures as
50
well. The degree of osseointegration of the fixture is dependent on factors such
as skull thickness, bone density, nutritional status, and surgical technique at
implantation as excessive heat with drilling speed or torque can damage the
bone structure (Kohan, Morris, & Romo, 2008).
Once some osseointegration has occurred the external BAHA transducer or
sound processor to be loaded onto the abutment. This usually takes place 4 - 6
weeks post-operatively for adults (Snik et al., 2005) and up to 6 months post-
operatively for the paediatric population (Weber, 2002). In the two-stage
process, the titanium fixture is first implanted, followed by the abutment
connection once osseointegration has occurred (3 to 6 months post-surgery)
(Weber, 2002). Once the sound processor is loaded onto the abutment it
consequently becomes mechanically connected to the mastoid region of the
temporal bone, part of which is the cochlea.
Potential risks with BAHA surgery are paraesthesia (sensation of numbness of
the skin), osseonecrosis (death of bone cells due to decreased blood supply),
subdural haematoma (blood gathering within the inner meningeal layer of the
dura, usually resulting from a trauma to a vein), meningitis, perforation of the
dura with possible cerebral spinal fluid (CSF) leak, and/or loss of the skin graft
(Weber, 2002).
3.1.2 Direct bone conduction
In direct bone conduction, the amplified sound is transmitted to the cochlea via
bone conduction (BC) of the temporal bone in which the cochlea is encased.
The bone conduction hearing aid (BCHA) consists of a behind-the-ear hearing
aid hard-wired onto a spring loaded steel headband to a bone conduction
transducer. These devices rely on an arrangement that ensures a firm
mechanical connection between a vibrating transducer and the temporal bone
using pressure. This transducer vibrates under the control of sound picked up
by the microphone and electronics. In the case of the BAHA, sounds are
detected by the microphone on the sound processor and converted into
vibrations by a transducer that is attached to the abutment connected to the
titanium implant. This vibration is then transferred through bone to the either
51
cochlea or to both cochleae. In the case of UPSHL the transmission is to the
cochlea on the contralateral side of the affected ear. The mechanical vibrations
stimulate the nerve fibres within the cochlea to allow electrical impulses to be
transmitted and interpreted by higher auditory pathways up to the level of the
auditory cortex.
Stenfelt (2005) reported that there are five components to BC: (i) the external
ear component (which is generated along the ear canal by sound), (ii) middle
ear inertia, (iii) inertia of the cochlear fluids, (iv) compression of the cochlear
walls, and (v) pressure transmission from the cerebrospinal fluid. Direct bone
conduction may primarily involve the last three of these components of BC.
The major advantages of direct bone conduction are that it has minimal effect
on the normal hearing function and that amplified sound is frequency specific
(Stenfelt et al., 2000). Therefore, the normal sound path through the ear canal
to the cochlea is not obstructed. The external ear component of bone
conduction is not affected, resulting in the absence of the occlusion effect.
However, unlike conventional BC devices, the BAHA provides direct bone
conduction via placement of a skin penetrating titanium abutment. Thus, BAHA
users do not experience dampening of amplified sound by hair, skin, soft tissue,
cartilage and other tissue structures (Stenfelt, 1999). Additionally, the BAHA
does not rely on mechanical pressure being exerted on the skin over the
temporal bone; issues of tissue breakdown, reported with traditional BCHAs are
negated.
52
3.1.3 BAHA sound processors
BAHA fittings occur in specialist centres with the team consisting of at least an
otolaryngologist and an audiologist (Snik et al., 2005). After surgery and the
osseointegration period has occurred, the removable external component
(called the sound processor) is fitted to the abutment by an audiologist.
The first individual was implanted in Gothenberg, Sweden in 1977 with an Entific
Medical Systems device. The initial ear level BAHA device was the HC100
(Head worn Classic) released in 1985, followed by the stronger NAS HC220
(superbass) - body worn device. In 1993, an updated and commercially
released model of the ear level version was marketed as the Classic 300 as
shown in Figure 3.4. It was suitable for individuals with a sensorineural hearing
loss component in the better ear of up to 30 to 35dB HL formulated from the
three frequency average (3FA) of 0.5, 1 & 2kHz for BC thresholds (Snik et al.,
2005), whilst others recommend fitting up to the 3FA of the BC thresholds to 45
dB HL (Entific Medical Systems, 2001; Roberts et al., 2005).
Figure 3.4. Side view of the Classic 300 ear level sound processor.
Note. From (Entific Medical Systems, 2005b).
The next ear level BAHA was the Compact model, which became available in
1999/2000 following a modification in the abutment. This was the main sound
processor model involved in the study as shown in Figure 3.5.
53
Figure 3.5. Subject wearing Compact ear level sound processor Note. From (ESIA photography, 2006, taken by study author)
The new abutment introduced the snap fitting with a conical shaped abutment
for improved hygiene as it had a lower profile and smoother contours than the
previous bayonet coupling. This improved the ease and efficiency of cleaning.
The snap coupling also eliminated the use of 0-rings that had to be replaced by
the audiologist or BAHA wearer (Entific Medical Systems, 2000). The sound
processor is connected to the protruding abutment by a snap coupling
technique. Rotation to snap on the device is recommended by the manufacturer
as it reduces the pressure placed on the abutment when attaching and
removing the sound processor from the head. The snap coupling was designed
as a safety feature. If the BAHA sound processor is bumped accidentally, it
easily disconnects from the abutment. This reduces the risk of potentially
dangerous forces being applied to the abutment.
The sound processor is a hearing aid with the key components of a microphone,
an amplifier, a receiver, a battery, with its coupling mechanism connected to the
percutaneous abutment. The microphone converts the sound into electricity,
while the amplifier increases the strength of the electrical signal requiring power
via the battery. The receiver converts electricity back into sound. Microphones
and receivers are both referred to as transducers as they alter one form of
energy into another (Dillon, 2001). The receiver contains a heavy mass that is
shaken by the electrical current passing through a coil that also shakes the case
of the sound processor. The snap coupling mechanism allows the transfer of
mechanical vibrations to directly vibrate the abutment and implant within the
54
skull. The Compact model was reported to be an improvement from the original
Classic 300 ear level model as it had output compression (AGCo) to improve
sound quality and listening comfort, and to reduce distortion from loud sound
inputs such as noisy environments with sudden high intensity inputs (Lin et al.,
2006; Tjellstrom, Hakansson & Granstrom, 2001). However, it still has an
analogue class D output amplifier, which does not allow digital signal processing
of the input component of the signal. However, the advantage of a class D
output amplifier is that it is very powerful with a low level of distortion, but
efficient in battery consumption for its size (Dillon, 2001).
The Compact was also smaller than Classic 300, which made it cosmetically
appealing to users. However, the maximum output is lower, therefore would
have been an audiological consideration when individuals with an older sound
processor were considering upgrading to the Compact. Individuals who have
worn an amplification device become used to the sound quality and loudness
that their device delivers. Particularly with individuals with a conductive hearing
loss, output power of the device is important as the nature of their hearing loss
causes attenuation of sound to the cochlea, therefore, they require as much
power output from their hearing device as possible to overcome this.
The Compact model was recommended to be used with individuals who had a
four frequency average (4FA) of BC thresholds (0.5, 1, 2 & 3kHz) equal to 45 dB
HL or better (Entific Medical Systems, 2001). Sound input to 60dB sound
pressure level (SPL) could be processed properly by the BAHA Compact worn
on its maximum settings due to the output compression (Snik et al., 2005).
Sounds of 60dB SPL include speech at normal conversational level but not a
raised voice. The overall gain of the Compact was comparable to the Classic
300 (Snik et al., 2005). It is standard practise to recommend to users to wear
the device on mid volume rather than its maximum level (volume 3). Wearing
the device on its maximum volume causes the device to become unstable and
more susceptible to collapsing the air gap between the internal transducer and
its housing. If the individual does wear their BAHA on the maximum volume for
normal listening situations, it does not allow the ability to increase the volume
when the need arises from greater challenging situations. Constantly using the
55
BAHA on maximum volume suggests that the device is not strong enough for
the hearing loss, the sound processor may be faulty; or the abutment could be
loose and not allowing effective vibration of the skull and cochlea. If the BAHA
system is working correctly, BAHA users should not need to use their device at
or near its maximum settings due to the efficiency of direct bone conduction via
a percutaneous system deliver sound to the cochlea (Snik et al., 2005).
Snik et al. (2005) also recommended that the Compact device be used with
individuals with a sensorineural hearing loss component of 30dBHL or less, as
the transducer has a lower maximum output than the Classic 300. This would
only be the case for individuals who initially were fitted with the stronger Classic
300 device and wanted to be up-graded to the Compact. Due to the difference
in power output, if the individual’s loss averaged 45dB HL across their bone
conduction, they would not perceive enough power with the Compact compared
to their old device.
A stronger and more powerful version of the BAHA released by Entific Medical
Systems in 1999 was the Cordelle II (Snik, Bosman, Mylanus, & Cremers,
2004). It consisted of a body worn amplifier connected to the transducer via a
cord. The fitting range of the BAHA was extended with the Cordelle II to greater
severity of mixed hearing losses. The sensorineural hearing loss component
was recommended to range from 30 to 60dB HL with those individuals who
were unable to be fitted with conventional air conduction hearing aids (Snik et
al., 2005).
In March 2005, Cochlear Limited (Australia) successfully acquired Entific
Medical Systems, AB (Sweden). Since this acquisition, two new products have
been commercially released: the Divino in 2005, (which is an updated version of
the Compact), and the Intenso in 2007 (a stronger ear level BAHA, similar to the
Classic 300) as shown in Figure 3.6 and Figure 3.7.
In the individual’s assessment period, a trial of the BAHA device is limited to a
transcutaneous application. Snik et al. (2005) recommended that the stronger
device Classic 300 was more appropriate than the Compact during this trial
56
period. Both the Compact and Classic 300 devices are no longer available.
Thus it is now recommended that the stronger Intenso be used for the
transcutaneous or pre-operative trial (Flynn, 2008).
Figure 3.6. Divino model, ear level sound processor. Note. From(Cochlear Limited, 2008a)
Figure 3.7. Intenso model, ear level sound processor. Note. From (Cochlear Limited, 2008b)
The Divino has the following features not available in the Compact device:
digital sound processing (DSP), flexible adjustment for tone and automated gain
controls (AGCO) to improve sound quality for individual needs, and two
programmes (one for noisy listening environments, and the other for quiet
situations). Furthermore, it is the only sound processor model to have an in-
built omni-directional/directional microphone allowing improved speech
intelligibility and discrimination in noise (Cochlear Limited, 2005). The features
of the Compact and Divino sound processors are compared in Appendix I. The
timeline of the release of the different BAHA sound processors and FDA
approvals since 1977 is shown in Figure 3.8.
57
Figure 3.8. Timeline of introduction of BAHA sound processors.
Note. From (Cochlear Limited, 2008c).
58
3.1.4 Post surgical complications and management
Once an individual has been fitted with a BAHA, care of the implant site is
required on a daily basis. The implants are MRI safe if future scans of the
temporal bone are required (Robinson et al., 1996; Weber, 2002). This is
particularly important in the VS group of patients who require scanning following
tumour removal and in children who may require a MRI in their lifetime.
The percutaneous abutment of the BAHA has been reported to be safe and
have limited complications. If complications do occur, they are generally easily
treated (Snik et al., 2005). In the paediatric population a major risk is implant
failure due to direct trauma to the abutment during the critical stage of
osseointegration, which may loosen, damage and/or completely remove the
abutment. A loose abutment can cause irritation or failure of osseointegration,
leading to inflammation or infection (Weber, 2002). Trauma is a significant
factor in abutment loss in the paediatric population as children engage in a
higher level of active play that could lead to the abutment being knocked in the
first few months following implantation.
There are two main factors which contribute to skin reactions or post-operative
complications following BAHA surgery. The first factor relates to the surgery.
Surgery for a BAHA needs to be meticulously performed with adequate removal
of excess subcutaneous tissue; a thin, hairless graft needs to be created;
adequate cooling is essential during drilling in order to minimise tissue trauma; it
is important that reduction of overall heat generated is performed with irrigation
as excessive heat affects osseointegration; and careful post-operative care is
required to ensure correct pressure is placed over the skin graft (Lekakis,
Najuko, & Gluckman , 2005). There have been improvements over the thirty
years in the surgical techniques used to implant the BAHA system. Excessive
residual soft tissue is thought to be a principle factor involved in post-operative
skin reactions due to the mobility of this skin around the abutment site (Stalfors
& Tjellstrom, 2008).
The second factor that contributes to skin reactions is the subject’s ability to
clean the abutment and the surrounding skin area adequately. Both surgical
59
and audiological follow-up of the abutment is important. Feedback about the
subject’s cleaning procedure is important to ensure sufficient daily cleaning. As
the abutment is percutaneous, the skin site adjacent to the titanium implant is
the main area of focus and requires particular care to be free of debris when
daily cleaning around the abutment occurs.
Other reasons for skin reactions are hair follicles remaining in the graft area,
bacterial infections and allergic reactions to titanium. If the hair follicles are not
adequately removed from the skin graft, their presence can cause either foreign
body reactions, or the protein component of hair keratin itself can cause
inflammatory reactions (Stalfors & Tjellstrom, 2008). The bacteria -
Staphylococcus aureus has also been reported to cause adverse skin reactions,
with some BAHA clinics systematically prescribing antibiotics post-operatively.
However, Stalfors & Tjellstrom (2008) reported that bacterial infection was a
secondary sign of inflammation as clinics that do systematically administer
broad-spectrum antibiotics post-operatively also report skin reactions. Another
cause of skin reactions is an allergic reaction to titanium.
Evaluation of the long-term reliability of the device with its traditional application
for conductive and mixed hearing losses has shown high reliability. A study of
147 patients who had undergone a total of 167 BAHA implantations, showed
only 0.1% had infection requiring revision surgery, whilst 93.3% of patients had
no reaction to the placement of the abutment (Hakansson et al., 1990).
Reliability is dependent upon osseointegration of the implant. The rate of
failures within the paediatric population has been reported to range between
5.8% and 15% (Tjellstrom et al., 2001). Adult failure rates vary amongst
studies, but are smaller than paediatric rates, reported to range between 2.5%
and 3.5% (Badran, Arya, Bunstone, & Mackinnon, 2009). In a study of 149
adult subjects who had undergone BAHA surgery failure rate of 3.4% due to
loss of osseointegration following local infection and pain within the first four
months of implantation, resulting in extrusion of the fixture (Badran et al., 2009;
House & Kutz, 2007).
60
Post-operative skin reactions are common issues that are seen in the BAHA
clinics. For example, the grafted skin can thicken around the abutment due to a
local skin infection (Davids, Gordon, Clutton, & Papsin, 2007) as shown in
Figure 3.9. The reported rate of skin reactions varies from 3.4% to 39.6%
(Lekakis et al., 2005). However, Snik et al. (2005) reported that 90% of implants
remain free of serious skin reactions during the follow-up period. Prevention of
skin infections or overgrowth requires careful, regular hygiene to reduce skin
thickening and graft site ulceration (Davids et al., 2007). Treatment of skin
reactions is by local application of antibiotics and/or steroid ointment (Snik et al.,
2005). Skin overgrowth is reported to occur equally among the adult and
paediatric populations (Tjellstrom et al., 2001). A follow-up study of sixty-seven
BAHA subjects fitted for chronic suppurative otitis media in Birmingham listed
complications that included: failure to integrate; late loss of fixtures; loosening of
the abutment; minor skin loss around abutment; and/or minor or major wound
infections (Macnamara et al., 1996).
Figure 3.9. Photograph of one subject in this study’s abutment placement in mastoid bone. NB Photograph of a left ear with some crusting and scabbing along the border of the skin flap. Note. From (ESIA photography, 2006, taken by study author)
Due to the risk of trauma to the abutment, contact sports are not recommended
in the early period after surgery. However, after medical clearance is given
post-operatively, there are minimal restrictions as to what activities the individual
can engage in.
61
3.2 Use of BAHA in hearing rehabilitation
Over 50,000 individuals worldwide have been implanted with a BAHA device in
its various applications (Tjellstrom, 2008). The common use of the BAHA in
rehabilitation of conductive hearing losses has been well-documented since the
1980s (Mylanus, van de Pouw, Snik, & Cremers, 1998). Previously, aiding
some of this population had been difficult relating to the use of ear moulds. The
use of the BAHA for fitting hearing losses, particularly in the paediatric
population, has been revolutionary for those children born with congenital aural
abnormalities, such as bilateral atresia or microtia, and for those individuals who
had chronic conductive hearing losses, such as draining mastoid cavity or
recurrent otitis externa, which restricted the use of conventional air conduction
hearing aids (Cooper, Burrell, Powell, Proops & Bickerton, 1996). Another
group of patients that can be fitted with BAHA for conductive hearing loss are
individuals with otosclerosis. Otosclerosis is a condition in which the middle ear
bone joints fuse together or to the oval window of the cochlea. The BAHA is
regarded as a third option for these individuals if they do not want or are unable
to benefit from a stapedectomy and /or fitting of conventional hearing aids
(Burrell, Cooper, & Proops, 1996). Traditionally, these individuals would have
been fitted with a BCHA, or an air conduction hearing aid (ACHA) whenever
there is medical clearance.
The major disadvantage of the BCHA is the force required on the skull to enable
effective sound transmission and functioning of the device. Daily and long-term
use of these devices could result in pressure and tension headaches, skin
irritation, itchiness, inflammation, and/or pressure ulcers on the mastoid bone
(Burkey, Berenholz, & Lippy, 2006; Davids et al., 2007; Mylanus, 1994; Snik et
al., 2004). Snik et al. (2005) reported that long-term, constant use of a BCHA
could cause a force resulting in furrowing in the squamosa of the skull in young
children. This indentation of the bone may be due to the paediatric bone being
thinner, averaging 2mm at 5 years of age, and consisting of a lower mineral but
higher water content than the adult skull, therefore having greater susceptibility
to structural changes with pressure (Kohan et al., 2008). Experimental data has
shown that percutaneous transmission (direct bone conduction) as used in the
BAHA system, is 10-15 dB more efficient than transcutaneous transmission via
62
bone conduction hearing aids (Hakansson, Tjellstrom, & Rosenhall, 1984;
Tjellstrom et al., 2001).
A number of features of the BAHA have been identified as increasing user
compliance of this device when compared to the traditional BCHA: elimination of
the soft tissue dampening with direct bone conduction, improved sound quality,
and increased comfort and reliability. One result is the enhancement of speech
and language development when the BAHA is fitted at a young age (Spitzer,
Ghossaini, & Wazen, 2002). However, contradictory findings were reported in a
study measuring skin thickness and subcutaneous tissue of fifty-seven BAHA
users. No correlation was found between aided BC thresholds of
transcutaneous transmission of sound or percutaneous transmission to skin
thickness (Mylanus, Snik, & Cremers, 1994). These authors concluded that
thickness of skin and subcutaneous tissue could not be pre-operative indicators
of BAHA success, suggesting that there could be other reasons for better
functional bone conduction thresholds obtained in testing with the BAHA
compared to the BCHA.
For some individuals with conductive hearing losses the disease can reoccur
but periodically, particularly with discharging or perforated ears. These
individuals may have been initially fitted with a conventional ACHA, but were not
consistent users due to recurrent ear infections. In a study 90% of subjects with
chronic suppurative otitis media experienced significantly less discharge when
fitted with a BAHA device than when wearing their ACHA. This reduced return
visits to Ear, Nose and Throat (ENT) departments (Macnamara et al., 1996).
Other studies of BAHA users who had previous experience with ACHA
amplification, found that BAHA implantation should be recommended when the
individual has an air-bone gap of 25-30dB, and/or has chronic ear problems
which medically contraindicate the use of ACHA, such as chronic otorrhea and
otitis media (Mylanus et al., 1998). These findings were based on audiometric
testing and an in-house designed questionnaire results from thirty-four subjects
tested with an ACHA and their BAHA. Greater than sixty percent of the subjects
reported a preference for the BAHA compared to the ACHA because of
63
decreased occurrence in ear infections leading to decreased visits to ENTs, and
improvements in quality of sound, speech in quiet, and reduced acoustic
feedback. The questionnaire results also showed that subjects had no preferred
aid for situations involving the perception of speech-in-noise when compared
with their previous ACHA to the BAHA, despite speech-in-noise test results
showing that only 12% of subjects performed significantly better with their ACHA
than the BAHA. Mylanus et al. (1998) concluded that although there was no
advantage for either aid regarding speech understanding in noise due to the
difference in objective and subjective results, BAHA is the acceptable choice if
an ACHA is contraindicated with individuals with chronic ear disease.
A long-term study of the conventional BAHA use with a conductive hearing loss
in thirty-nine subjects has shown 5% of subjects were non-users at least four
and a half years after follow-up (Snik, Dreschler, Tange, & Cremers, 1998b).
Similar long-term studies of BAHA usage five to ten years post-fitting showed
that almost all of the subjects were still using their BAHA on a daily basis and
were satisfied with the result (Snik et al., 2005).
Hol, Bosman, Snik, Mylanus & Cremers (2005) investigated subjects with an
acquired unilateral air-bone gap (>45dB) who had been fitted with BAHA on the
worse hearing ear. Results showed significant improvements in speech-in-
noise tests with spatially separated noise and sound sources. Directional
hearing tests showed improvement. However, many subjects had fairly good
scores unaided, which lead the researchers to question that these subjects may
have adapted to their hearing loss.
3.3 Application of BAHA with UPSHL
3.3.1 How the BAHA works with UPSHL
The principle of placing the BAHA in the mastoid region of the temporal bone on
the affected cochlea side is that with direct bone conduction, the sound would
be transferred from the unaidable ear via the skull to the opposite functioning
cochlea as shown in Figure 3.10. The end result would give the individual using
the BAHA a perception of sound from the non-functioning side.
64
Figure 3.10. The transfer of sound across to the non-affected cochlear on the contralateral side from direct bone conduction using the BAHA.
Note. From (Entific Medical Systems, 2005a).
The transfer of sound between cochleae has been experimentally shown by
Brandt in 1989 that in specific conditions, the contralateral cochlea receives
better stimulation than the ipsilateral one (Snik, Beynon, Mylanus, Van der
Pouw, & Cremers, 1998a). The limitation of BAHA as a transcranial CROS
device is that it is not expected to have any significant effect on directional
hearing or binaural summation, but in certain listening situations the BAHA may
compensate for head shadow effects (Snik et al., 2004). Snik et al. (2005)
reported that, in principle, fitting a BAHA system would not result in
stereophonic hearing, as there is only one working cochlea.
The manufacturer’s initial criteria for candidacy were that hearing was within
normal air conduction thresholds, with a pure-tone average (0.5, 1, 2 and 3kHz)
equal or better than 20dB HL in the better hearing ear, and/or individuals who
for some reason cannot or will not use an air conduction contralateral routing of
signal (CROS) hearing aid (Entific Medical Systems, 2001, 2003a). Further
audiological criteria for fitting of BAHA to UPSHL were outlined by Wazen et al.
(2003). They included air-conduction thresholds worse than 90dB HL on the
affected side, poor ability to discriminate speech measured as a speech
discrimination score of worse than 15%, and normal hearing on the contralateral
side measured as pure-tone thresholds better than 20dB HL. These criteria
have since been used by other clinics (Ghossaini, 2006).
65
3.3.2 Background studies Although the BAHA (Cochlear Limited, Australia) is widely known implanted
bone conductor device, there was another partially implanted bone conduction
hearing aid device used in the 1980’s, called the Audiant bone conductor. This
system had a magnet implanted into the temporal bone, which was
transcutaneously coupled with an external induction coil positioned on the skin
directly above it (Mylanus et al., 1994). It was developed by Xomed-Treace,
Jacksonville, USA (Snik, et al., 1998a).
In the early 1990’s, experimental use of the Audiant implant for acquired UPSHL
showed some success with a small number of individuals who had undergone
VS removal (Pulec, 1994). The Audiant implant was used in this population of
acquired UPSHL subjects based on the principle that the interaural attenuation
for bone-conducted stimuli is lower than that required for conventional air-
conduction stimuli from the affected ear to the contralateral cochlea.
The implant proved to be unsuccessful in improving speech recognition in noise,
and sound localisation – due to lack of sufficient gain resulting from the
transcutaneous design of the system. Therefore, individuals did not use the
device regularly (Weber, Roush, & McElveen, 1992). Other reported issues with
the device were inflammation, pressure on the skull, and the need for a high
number of device repairs. This resulted in 65% of Audiant implantees being
poor users or non-users (Snik, et al., 1998b). As the Audiant implant device
was withdrawn from production due to issues with its reliability and safety (Snik,
et al., 1998b), long-term outcomes in this implanted population are unknown.
Currently, the BAHA is the only implantable bone conduction hearing system
available.
Despite bone conduction not being as efficient for hearing as air conduction for
most hearing losses, particularly pure SNHL, this is not the case for single sided
deafness, as the device is attached close to the cochlea for bone conduction
(Stenfelt & Goode, 2005). The mean transcranial attenuation of bone
conducted signals is around 10dB, thus the intensity of sound is not the same
66
level in the two cochleae, and hence providing a bilateral benefit with BAHA
(Breitholtz, 2008). Despite this, amplification by transcranial BC in a UPSHL
was not fully explored until 2000. Entific Medical Systems, AB (Sweden) had a
well-established, reliable, commercial product that utilised direct bone
conduction, marketed as the BAHA. Approval for the use of the BAHA system
for unilateral deafness was granted by the regulatory bodies of the European
Community Certificate (CE mark, European Union), and Therapeutic Goods
Administration (TGA, Australia) by 2003 (Roberts et al., 2005). This resulted the
BAHA being utilised as a transcranial CROS system. The term BAHA CROS
has been a suggested term to differentiate between the traditional application of
BAHA and BAHA use with UPSHL (Snik et al., 2005). However, in the current
study, as BAHA CROS is not a common term used in the literature, the term
BAHA has been used for all of its applications including UPSHL.
At the time of this study’s commencement in 2004, the literature on the BAHA
for UPSHL was limited. Although many studies have been published about the
BAHA for the management of UPSHL since then, there are four key published
articles on the subject of BAHA on UPSHL that are often referenced. The four
studies included one study that was carried out in France (Vaneecloo et al.,
2001), two in the United States (Niparko et al., 2003; Wazen et al., 2003) and
another in the Netherlands (Hol, Bosman, Snik, Mylanus, & Cremers, 2004).
Each of these studies is limited in several ways. The audiometric criteria,
counselling of potential candidates, and outcomes were not adequately defined.
In addition, the BAHA manufacturer, Entific Medical Systems did not provide
adequate information for health professionals to determine the best candidate
for the latest application of their device in their guidelines for audiologists (Entific
Medical Systems, 2003a).
The French study, Vaneecloo et al. (2001) was first to describe the use of the
new application of the BAHA with 29 subjects with unilateral total deafness
resulting from various aetiologies. The researchers found that their subjects
had improved speech recognition in noise and a reduction of the head shadow
effect after being fitted with a BAHA Compact device. The subjects’ ages
ranged from 9 to 78 years old, i.e. they included children, which were not fully
67
discussed within their published study. The research also included subjects
whose unilateral deafness was either congenital or had been acquired early in
life. There is limited information in the report about the development of
understanding speech in noise and localisation abilities in congenital or early
onset of UPSHL; differentiating a group on the basis of their age of onset within
their overall subject group results would have been beneficial. The subjects’
audiometric information was limited but it was noted that some subjects had a
hearing loss in their “good” ear that would benefit from a conventional hearing
aid. The “average” hearing in the “better” ear was 33dB but the authors did not
specify from which particular frequencies this “average” was obtained.
The authors reported their subjects’ pre and post-operative results in three
areas: spatial discrimination in noise, a multidirectional test of prosthetic gain
and spatial sound location testing. However, they did not report the results in
regards to different subgroups of aetiologies or age groups. The authors
reported that the subjects gained the ability to localise, which was termed
“monaural pseudo stereophony” following the fitting of the device. Outcome
measures of the subjects’ functional benefit from the device were obtained.
However, this was done retrospectively with the GHABP questionnaire being
sent to the subjects post-operatively. This retrospective approach required the
subjects to recall their pre-operative difficulties, whereas the post-operative
outcome measures were recorded almost immediately, as the questionnaires
were mailed to the subjects 6-8 weeks following the fitting of the device. Due to
the short time span post-fitting, it gave limited information regarding long-term
use of the device. The authors reported that three subjects had discontinued
BAHA usage, one due to lack of effectiveness, whilst the other two subjects
gave non-specific reasons for discontinued use of the device.
In the United States, Niparko et al. (2003) compared ten adult subjects with
unilateral deafness who had trialled a conventional contralateral routing of signal
(CROS) hearing aid for one month. These subjects then proceeded with BAHA
surgery and fitting. The audiometric criteria in this study was clearly defined: the
pure tone average of the three frequencies 0.5kHz, 1kHz and 2kHz was >90dB
and speech discrimination (SD)<20% in the unilateral deaf ear, while hearing in
68
the better ear had a pure tone average <25dB and SD>80%. The authors
reported that one of their subjects had a “sudden unilateral sensorineural
hearing loss associated with bilateral active chronic suppurative otitis media”,
which suggested there was a mixed loss in the poorer ear. This subject fitted
the audiological criteria because of their air conduction thresholds. However,
there would have been an air-bone gap in both ears, which may suggest
different hearing outcomes to the other subjects due to the better bone
conduction thresholds of this subject.
The subjects in this study reported greater benefit from the BAHA device
compared to CROS amplification. Speech testing in noise results showed an
advantage to the BAHA over the CROS in all the test conditions, with the BAHA
performance in three of the five hearing in noise test (HINT) results reported to
be statistically significant. However, this study was not able to show any
improvement in sound localisation abilities for either device when compared with
the subjects’ unaided results.
The Abbreviated Profile of Hearing Aid Benefit (APHAB) and GHABP surveys
were administered to subjects initially following their four-week trial of the CROS
amplification system, and again following implantation and fitting of a BAHA
device. The study reported that subjects had greater subjective benefit from the
BAHA compared to the CROS aid. The authors reported that 90% of the
subjects wore their BAHA device for most or all waking hours while the
remaining one subject reported wearing the BAHA an average of two hours
daily. This subject’s reduced BAHA usage was reported to be due to the limited
benefit that the device provided in a noisy work environment, and that the
device intensified the subject’s pre-existing tinnitus in the non-affected ear.
Overall, no long-term outcome benefit data was obtained for either the CROS or
BAHA device in this study.
The third key study published by Wazen et al. (2003), was used as part of the
FDA approval process (based on the study’s findings in 2002) to expand BAHA
indications to include unilateral hearing losses, including single-sided deafness
(Spitzer et al., 2002). Their audiometric criteria included air conduction pure-
69
tone thresholds >90dBHL or maximum SD scores < 15% in the poorer ear, and
air conduction thresholds <20dBHL for the better ear (a four frequency pure-
tone average for 0.5, 1, 2 and 3kHz) rather than the traditional PTA3F.
Eighteen adult subjects from three centres were assessed after one month
CROS hearing aid trial prior to BAHA implantation. Audiological testing was
conducted with the contralateral (better) ear occluded using a noise-rated
earplug. Both objective and subjective results suggested that the BAHA
provided greater benefit than the trialled CROS aid. However, both of these
American studies had small groups of subjects, and did not report on device
usage for any longer than six to eight weeks post-BAHA implantation.
A fourth study by Hol et al. (2004a) of twenty subjects examined their
performance unaided, fitted with a CROS aid for one month and following
implantation with a BAHA. They reported improvements in speech-in-noise
perception when their subjects were wearing the BAHA in comparison to the
traditional CROS hearing aid. They asserted that the resulting improvement in
SNR scores was due to the BAHA decreasing the impact of the head shadow
effect. Their subjects’ responses on the Abbreviated Profile of Hearing Benefit
(APHAB) questionnaire indicated that BAHA was their device of choice. There
were several flaws to the study in that no technical details given about the fitting
of the CROS device, six of the subjects did not proceed to implantation after the
trial of the BAHA with no further follow-up, while nine of the subjects’ results had
been previously reported in another study (Baguley et al., 2006).
3.3.3 Recent studies
During the course of this study there have been marked changes to the BAHA
sound processors available to individuals, and an increased number of studies
on BAHA use in the population of UPSHL. A roundtable meeting held in
Nijmegen, The Netherlands in June 2004, was reported in an article by Snik et
al. (2005). One of the aims of the meeting was to create guidelines for the fitting
of BAHA for UPSHL supported by the European, Canadian and American BAHA
clinic representatives who attended. One of the recommendations was that the
term BAHA CROS be used to describe the use of BAHA with UPSHL to
differentiate its use from the traditional fitting of conductive or mixed hearing
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losses. The committee suggested a trial should be undertaken by the
prospective BAHA recipient with a BAHA device on a test headband placed on
the mastoid of the “deaf” ear prior to surgery (Snik et al., 2005).
They did not support placing a percutaneous implant for a BAHA during surgery
for unilateral transcochlear or translabyrinthine approach to VS tumour removal,
but suggested a sleeping fixture may be beneficial and could be utilised
following a period of adaptation by the individual to his/her post-operative
hearing levels (Snik et al., 2005). If considering placing a sleeping fixture, they
advised that pre-operative counselling with VS subjects should involve
audiological workup, determining hearing status of the non-affected ear as well
as counselling on post-operative amplification options, including the BAHA to
allow the individual to form realistic expectations.
As knowledge about using BAHA as a rehabilitation device for UPSHL has
increased, some papers have advocated counselling and amplification by either
a conventional CROS hearing aid system, a BAHA device or other assistive
listening devices when the individual with a UPSHL reports significant hearing
handicap pre-operatively (Humphriss, Baguley, Axon, & Moffat, 2006).
Studies have also been published questioning the efficiency of fitting a BAHA to
individuals with a UPSHL. Baguley et al.(2006) published a study questioning
the efficacy of using a BAHA for individuals with a UPSHL. They questioned the
efficacy of the research that was partly responsible for obtaining FDA approval
in the United States of America. This paper was published after a detailed paper
by Snik et al. (2005) that supported Baguley et al.’s comments regarding
implantation at the time of surgical removal of VS with a sleeping fixture.
Tringali et al. (2008) conducted a study on 118 subjects fitted with a BAHA for
UPSHL and 52 who had been fitted with a BAHA for a conductive hearing loss,
to evaluate their usage and satisfaction with their device. The UPSHL subject
group comprised of 92 subjects with a UPSHL following VS or meningioma
removal surgery, two with a UPSHL from idiopathic sudden deafness and 24
with a UPSHL from complications surgery of the middle ear. Subjects had been
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wearing their device an average of 22 months, and a maximum to six years.
The survey was administered by mail. The authors report that satisfaction and
quality of life rating was poorer in the UPSHL group than in the conductive
hearing loss group. They also recommended a comparative study of newer
powerful WiFi CROS system as this technology was not evaluated in previous
studies comparing CROS aids and BAHA for UPSHL. This study had
shortcomings because the questionnaire was administered retrospectively.
Furthermore, a condensed version of a published questionnaire was used in an
attempt to ensure a greater response rate.
Although the literature on fitting subjects with a BAHA for UPSHL is growing –
there are still many unanswered questions regarding the long-term outcomes for
individuals who do proceed with a fitting of a BAHA for their UPSHL. Evaluation
of short-term outcomes should extend to a period of at least three months, as
this is the general amount of time required for the acclimisation to any form of
amplification. Long-term outcomes need to be based on data longer than
twelve months post-surgery to ensure that possible difficulties or issues
regarding the fitting of the sound processor are overcome (Hol et al., 2004b),
skin infections around the abutment are addressed, repairs made to the device
if needed, and to ensure the subject is conversant with the device to give a true
indication of whether the device is effective rather than subjects giving positive
feedback based on a newly fitted device.
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Chapter 4: Purpose of the study
In light of the limitations of the discussed studies summarised in previous
chapters, data was required for an Australian perspective on the clinical use of
BAHAs. In addition, evaluation of the long-term efficacy of using this device in
the rehabilitation of UPSHL was warranted.
When this study commenced, the audiological manual for selection, evaluation
and fitting of individuals with BAHA (published by the manufacturer) referred
only to traditional uses of the BAHA (including the bilateral application), but did
not include the protocol for assessment nor fitting, of subjects with profound
sensorineural hearing loss in one ear (Entific Medical Systems, 2001). The
company recommended that the individual should first be tested with the device
attached to the test rod (a simulator of the bone conduction) whilst occluding the
better ear. The pre-operative testing procedures prescribed by the
manufacturer appeared too simplistic for this group of individuals given the
complexity of their hearing loss. The amount of recommended pre-operative
assessment was not congruent with the actual post-operative aftercare and
evaluation.
In general audiological clinical practice, as in all fields of medical and allied
health care, a solution is sought to ensure that the best outcomes are achieved
for each individual. Therefore, the three aims of this study were to evaluate the
changes to speech discrimination in quiet and in noise, along with self-reported
hearing difficulties with a BAHA, compared to the test-band and the unaided
conditions in individuals with UPSHL over a set time period. The second aim
was to determine if there were any practical or medical limitations with using the
BAHA as a rehabilitation tool for people with a UPSHL.
The third aim was to evaluate the self-reported hearing difficulties in the long-
term of subjects with a UPSHL who had been fitted with a BAHA, compared to
those who had been assessed for BAHA candidacy but did not undergo
implantation.
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The hypotheses of this study were:
1. For subjects with UPSHL, there will be significant improvements in
speech discrimination in quiet and in noise and in self-reported
hearing difficulties with a BAHA compared to the test-band and
unaided conditions.
2. For those fitted with a BAHA for UPSHL, there will be no medical or
practical limitations to the wearing of the device.
3. For the subjects who were not implanted, there will be no change in
their self-reported hearing difficulties in the long-term.
.
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Chapter 5: Material and methods
This was a three-year, prospective, self-controlled (the subjects were their own
control) concurrent study. This experimental study design was chosen as it
involved multiple audiological measurements for evaluating the clinical outcome.
This type of study design is often used in the early stages of clinical
development of treatments. As BAHA usage as a rehabilitation tool for a
UPSHL was a recent application, this was an appropriate study design. No
blinding was used in this study. Intra-subject and inter-subject variation was
evaluated for subjects with a UPSHL who had been rehabilitated with a BAHA.
A number of statistical measures were used in data assessment and these
results were compared to non-implanted UPSHL subjects. This study had a
three year time period due to three fundamental conditions:
(i) Osseointegration must occur before the sound processor is fitted.
(ii) The acclimatisation effect (adaptation to the sound) that applies to
all hearing aid fittings must be considered.
(iii) Long-term outcomes of BAHA usage by subjects with UPSHL
have not been extensively been published.
Qualified audiologists in two audiology centres used the same protocols to
conduct pre- and post-implant testing of the subjects as outlined below.
5.1 Subject selection
5.1.1 Subject inclusion criteria
The subjects in this study were recruited from the clinical caseload of two
Australian audiology centres: Lions Hearing Clinic - Implant Centre in Nedlands,
Western Australia, and Healthy Hearing & Balance Care in Bondi Junction, New
South Wales.
Selection criteria required subjects to have:
(i) A pure tone audiometry three frequency average (PTA3F= 0.5kHz,
1kHz and 2kHz) of ≤ 20dB HL (± 5dB HL), and/or maximum
speech discrimination (SD) of AB (Arthur Boothroyd) words (see
Appendix II) of ≥ 80% in the non-affected ear.
75
(ii) PTA3F of ≥ 91dB HL (± 5dB HL), and/or minimum SD of AB words
≤ 20% in the affected ear.
(iii) English as a primary language.
(iv) Referred by an otolaryngologist who had determined the cause of
the hearing loss, which could include idiopathic causality.
Gender, age or length of hearing loss did not influence subject selection;
however, a range of subjects was expected. Subjects were included on the
basis of their ability to manage the daily cleaning of the abutment, and good
dexterity that would allow correct attachment of the external sound processor.
The subjects were given an information sheet that described the study and their
involvement (see Appendix VIII). If they agreed to participate the subjects
signed a consent form (see Appendix IX), which allowed access to their private
medical files revealing details about their audiology results, otolaryngology
appointments and surgery. Records were coded to ensure subject
confidentiality.
Full pure tone audiometry threshold testing across the frequencies 0.25 to 8kHz
including unmasked and masked bone conduction on each ear was conducted
as appropriate. Using margin of ± 5dB HL once the pure tone three frequency
average (PT3FA) had been calculated was part of the criteria due to test-retest
variability with routine pure tone audiometry. The test battery also included
impedance measures and separate ear speech discrimination abilities in quiet
under headphones.
In this study, the term speech discrimination (SD) has been used when
determining candidates, as this term is commonly reported in the literature and
is used amongst Australian hearing professionals. The SD score of the subjects
was included as part of the protocols and was required to be less than or equal
to 20% at AB Max (maximum) under headphones in the affected ear. SD
testing is normally used to verify the audiometric thresholds in each ear.
76
Some of the subjects included in this study had borderline profound hearing
levels. Although these subjects do not fit the criteria of having 91dB HL or
greater PTA3F (pure tone three frequency average) in their affected ear, they
were included in the study because they presented with very poor SD (≤20%) in
their affected ear and were considered “unaidable” with conventional air
conduction hearing aids.
5.1.2 Subject recruitment
A multi-centre study was formed with another audiology centre in New South
Wales. The Lions Hearing Clinic (LHC) is part of the Ear Science Institute
Australia (ESIA), previously known as the Lions Ear & Hearing Institute (LEHI).
Both centres were specialised BAHA clinics involving a team of audiologists and
otolaryngologists with previous experience with surgery and the fitting of BAHA
devices. The original subject inclusion criterion was restricted to recruiting
individuals following skull base surgery. Due to the limited number of subjects
available with skull base surgery resulting in a UPSHL, the subject inclusion
criteria was extended to include acquired and congenital UPSHL of varied
aetiology.
Subjects were referred to the two specialised BAHA centres by their general
practitioners to investigate either the causality of their hearing loss and/or the
possibility of being fitted with a BAHA. The subject was assessed by an
otolaryngologist to determine candidacy, and then referred to other team
members for pre-operative assessment and counselling, which included a two-
week device trial with the BAHA on both hard and soft headbands. After this
trial, the team used subjective feedback from the subject, combined with both
pre-operative assessment and medical clearance, to decide whether to proceed
with BAHA implantation.
5.1.3 Study ethical approval
Approval of the study was granted in 2005 by the Human Research Ethics
Committee, Sir Charles Gairdner Hospital, Nedlands, Western Australia. To be
able to carry out the study, Healthy Hearing & Balance Centre arranged the
necessary approval from their ethical committee and authority. All subjects
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provided informed consent before participating in the study with their respective
centres.
5.2 Test equipment
5.2.1 General test equipment
The centres involved in this study required the following equipment: an
audiometer with two channels, an immittence machine with the ipsilateral
acoustic reflex function, the National Acoustic Laboratories (NAL) Speech and
Noise for Hearing Aid Evaluation CD (Australian Hearing, 2000), a measuring
tape/device, a CD player, two free-field speakers, an amplifier, and a sound
level meter. The calibration standards for the equipment are listed in Table 5.1.
A two free-field speaker set up is not common to all audiology booths due to the
size restraints of some causing standing waves and inaccurate results. Healthy
Hearing & Balance Care installed a second free-field speaker to participate in
this study.
Table 5.1
Calibration standards of equipment used during testing procedure.
Equipment Brand Model Calibration Standard (if applicable) Audiometer Starkey Acoustic
Analyser AA30 AS/NZS 1269.4:1998; AS 1591.2 (1987 -
zero reference for calibration of pure tone audiometers)
THD-39P headphones
AS IEC 60645 (2002-Electroacoustics-audiological equipment)
Radio Ear B-71 bone transducer
AS 1591.4 (1995- bone conductor)
Amplifier Interacoustics power amplifier
AP70
Free-field Speakers
JBL Incorporated UBL LX40 ISO 226 and IEC 645-2 or equivalent
Immittence Machine
Grason-Stadler Tympanometer
GSI-38 AS 2586:1983; AS 1591, parts 1 and 2 in respect the appropriate clauses and/or in accordance with the manufacturer’s specifications indicated and adjusted to meet the requirements of the standard.
Sound level Meter
Rion Precision Intergrating
NL-11 Calibrated to manufacturer’s standards
CD player Panasonic Portable SL-SI20 Soundproof
Complied with ANSA with background noise levels of less than or equal to 30dB (A)
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5.2.2 BAHA test equipment
Both audiology centres had BAHA test equipment kept in stock that was
supplied by the BAHA distributors. It included test rods (Figure 5.1), soft
headbands, Compact, Classic 300, Divino and Intenso test and loan devices,
and BAHA hard test headbands as show in Figure 5.2.
Figure 5.1. Test rod device used in pre-operative evaluation
Note. From (Entific Medical Systems, 2005e).
Figure 5.2. Photograph of Compact BAHA on test band
Note. From (ESIA photography, 2006, taken by study author)
5.2.3 BAHA setting protocols
No changes were made to the factory settings of the BAHA gain trim
potentiometer located inside the battery compartment of the Compact device (as
recommended by the manufacturer (Entific Medical Systems, 2003a) during the
pre-operative testing. The tone potentiometer on the back of the Compact was
adjusted depending on the user’s subjective perception of sound, and its
position recorded. This tone potentiometer adjusted the device’s low frequency
response.
79
During the study, the Divino model was commercially released. This model had
both an omnidirectional and directional microphone setting as opposed to the
Compact model, which only had an omnidirectional microphone setting.
Therefore, all testing conducted with the Divino model used the omnidirectional
program setting. The electrical components and acoustic output of the two
devices were similar as shown in Appendix I; therefore it was appropriate to use
either model.
5.3 Test protocols
A test protocol manual was produced for use in both of the study centres. The
study data collection forms that were supplied by LHC included revised Arthur
Boothroyd (AB) word lists (Appendix II), a speech-in-noise flow-chart (Appendix
III), questionnaires (Appendix IV, V and VI), revised Bamford-Kowal-
Bench/Australian version (BKB/A) sentence lists (Appendix X), and subject data
sheets (Appendix XI). The results were entered on-line by the audiologists after
testing was conducted. This on-line database was developed and maintained
by ESIA.
The two participating centres conducted the study data collection as part of their
clinical workload. Along with the pre-operative assessment, individual
audiologists at the centres provided discussion about the BAHA device and
counselling. Handouts and information about audiological services were given
to the subjects. The subjects trialled the BAHA test device whilst wearing the
test band. They also listened to the device on the test rod. Subjects were
encouraged to trial either a Compact or a Classic 300 device (depending on
availability) on a soft and hard test band (as shown in Figure 5.3) for up to two
weeks to help facilitate their decision of whether to be implanted or not.
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Figure 5.3. Version of the test band to trial BAHA device. Note. From (Cochlear Limited, 2008c). 5.3.1 Pure tone audiometry testing
Routine audiometric testing was conducted at the pre-operative assessment to
determine hearing status if recent testing had not be performed. Testing was
administered in a calibrated soundproof booth. Pure tone air conduction (AC)
and bone conduction (BC) thresholds were measured to obtain accurate hearing
status of the subject using standard audiometric procedures on fully calibrated
equipment. Air conduction thresholds were obtained at the frequencies 0.25 to
8kHz, and BC thresholds were obtained at 0.5, 1, 2 & 4kHz. Whenever a AC or
BC threshold exceeded the maximum output of the audiometer, 5dBHL was
added to the maximum level when calculating the PTA3F.
5.3.2 Immittance audiometry testing
Immittance data was obtained using a calibrated automatic tympanometry
immittance machine. Tympanometry results and ipsilateral acoustic reflexes
were recorded at 0.5, 1, 2 and 4kHz. Immittance audiometry was performed to
ensure that subjects fulfilled the subject selection criteria. Each subjects’
immittance results had to show normal middle ear function (Type A
tympanogram) in order to collaborate the diagnosis of a sensorineural hearing
loss. Normal fluctuations in immittence, which can be found the general
population, were acceptable as long as the condition resolved itself back to a
normal tympanometry result. For example, a Type C tympanogram may have
occurred if the subject had temporary middle ear congestion and poor
Eustachian tube function due to a common head cold, but this should have
81
reverted back to a typical Type A tympanogram after the cold had resolved. If
the subject did not record a Type A tympanogram at the time of the assessment,
previous immittance results were examined to see if the subject was
demonstrating a transient middle ear condition or a long-term dysfunction.
5.3.3 Speech audiometry under headphones
The presentation of the speech test material was controlled using a compact
disc (CD) player attached to the audiometer. The test material administered
was AB word lists (see Appendix II), recorded by National Acoustic Laboratories
(NAL) Speech and Noise for Hearing Aid Evaluation Compact Disk (CD,
Australian Hearing, 2000). The AB word lists were presented at clinically
significant levels dependent on the subject’s individual hearing levels in each
ear. The lists were presented via headphones with appropriate clinical masking
noise placed in the non-affected ear. Presentation levels were calibrated prior
to each test session.
5.3.4 Free-field speech testing set up
Two identical free-field speakers, calibrated prior to testing, were used for free-
field speech testing. Testing was conducted with the subject sitting at a
distance of one metre from each speaker. One speaker was placed at 0
degrees azimuth of the subject’s head, and the other speaker at 90 degrees
azimuth or 270 degrees azimuth, depending on which stage of the testing
procedure was being conducted. This set-up for testing subjects was based on
protocols commonly used for testing bilateral cochlear implants. Three speech-
in-noise test conditions were used:
1. Speech and noise signals presented in front of the subject (S0:N0).
2. Speech presented at 0 degrees (S0) and noise presented at 90 degrees
on the right (N90).
3. Speech presented at 0 degrees (S0) and noise presented at 270 degrees
on the left (N270).
The complete testing set-ups are illustrated in Figures 5.4, 5.5 and 5.6.
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Figure 5.4. Position of speakers for speech testing in noise (S0:N270)
Figure 5.5. Position of speakers for speech testing in noise (S0:N90)
Figure 5.6. Position of speakers for speech testing in noise (S0:N0)
5.5.5 Free-field speech testing
Pre- and post-operative testing for speech discrimination followed the same
adaptive protocol of achieving a speech recognition threshold (SRT). Testing
consisted of single word lists in quiet and sentences in background noise. All
83
pre-operative speech testing was conducted with a BAHA test device on a steel
test band placed on the mastoid bone behind affected ear in free-field
conditions. Post-operative testing was conducted with the BAHA in-situ (on the
subject’s abutment) once it had been fitted and sufficient habituation time had
occurred, at least three months. Testing consisted of single word lists and
sentences being administered in quiet or with background noise. The non-
affected ear was not occluded during the speech testing.
5.3.6 Single word testing in quiet
Aided and unaided testing with AB words was administered in quiet conditions
with the subject directly facing a speaker. The lists of ten single words were
presented via CD recording of male voice with an Australian accent.
Three different speech in quiet protocols were used in this study:
1. Subjects were assessed preoperatively prior to 28 February 2005 were
tested with fixed presentation level of 40dB HL on the audiometer. These
subjects were classified as Group A subjects (n=24).
2. Subjects assessed between 28 February 2005 and 4 April 2006 were
required to obtain scores between 40% to 60% correct with 2dB changes
in the presentation level. These subjects were classified as Group B
subjects (n=10).
3. Subjects seen after 5 April 2006 were required to obtain scores between
48% to 52% correct with 1dB changes in the presentation level. These
subjects were classified as Group C subjects (n=22).
Therefore subjects were assessed pre-operatively and post-operatively
according to the particular speech in quiet testing protocols that was in use at
the time. When the adaptive procedure was used (Group B and Group C), an
average of two AB word lists at the same level was recorded to obtain the
presentation level (dB) of the words.
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5.3.7 Sentence testing in noise
Speech-in-noise testing using BKB/A sentences was conducted according to the
guidelines published in Australian Hearing Manual of Speech Perception, that is,
the speech was directed through the left channel and the babble noise through
the right channel. BKB/A sentence lists 8, 10, 16 and 20 were therefore
excluded from the test procedure. Scoring of the target words was conducted
with the audiologists using the Loose Key Word Scoring (LKW) method (Bench
& Doyle, 1979). BKB/A sentences were administered with multi-speaker babble
noise as the noise stimulus. Aided and unaided results were obtained for the
three speech-in-noise testing set-ups.
Three different speech-in-noise set-ups were used in this study as described in
section 6.3.4.
1. Subjects were assessed preoperatively prior to 28 February 2005 were
tested with fixed SNR levels. These subjects were classified as group A
subjects (n=24).
2. Subjects assessed between 28 February 2005 and 4 April 2006 were
required to obtain scores between 40% to 60% correct with 2dB changes
in SNR. These subjects were classified as group B subjects (n=10).
3. Subjects seen after 5 April 2006 were required to obtain scores of
between 48% to 52% correct with 1dB changes in SNR. These subjects
were classified as group C subjects (n=23).
Therefore subjects were assessed pre-operatively and post-operatively
according to the particular speech-in-noise testing protocol that was in use at
the time.
A speech-in-noise flow-chart illustrating the test protocol was designed for the
audiologists to follow when testing (see Appendix III). The final version of the
flow-chart showed the starting SNR of +5dB. The speech was held constant at
65dB SPL, with the level of noise varied systematically with 1 dB steps until the
85
subject’s response percentage correct score fell between 48% and 52%. A
second list was presented at the same level to increase the degree of accuracy
and a mean of two lists was taken as the subject’s score. The SNR and
presentation level were recorded, as the optimal SNR. Lists were scored using
the loose key word scoring technique and a speech-to-noise ratio required 50%
correct (SRT).
Conducting the post-operative testing in noise was predicted to be easier for the
audiologists to administer than the pre-operative assessment because the
optimal SNR had already been determined, and it was predicted that the
addition of the implanted BAHA would improve speech perception in noise. Two
lists were presented at previously determined optimal SNR in each of the three
conditions. Consequently, the speech and noise conditions were identical for
both pre-operative and post-operative speech testing, and thus a direct
comparison was possible.
5.3.8 Protocols for implanting subjects and post-surgical fitting of sound processor
All subjects who were implanted received the BAHA system with the snap
coupling abutment (Entific Medical System, AB Sweden and later Cochlear
Limited, Australia). They underwent the standard one-stage surgical procedure
whereby the device was implanted in the mastoid region of the temporal bone.
A 4 mm titanium fixture was implanted in subjects, with the exception of one
subject (S7) who received a 3 mm fixture. All subjects’ surgical and prostheses
were funded privately by the subject’s own private health fund.
After osseointegration had occurred (2-4 months post-operatively), the subjects’
abutments were sufficiently stable to support the loading of an external ear level
sound processor. Either a Compact or Divino model was fitted to the subject.
The first group of subjects who were implanted between 2003 and 2005
received the Compact model. The second group of subjects were fitted with the
Divino model in 2006, as it became available with TGA approval and private
health fund rebate.
86
Documentation of the abutment and repair issues was observed in the follow-up
visits including an examination of the skin condition around the abutment. It
was recorded in the subject's file if the otolaryngologist reported an infection.
The number of repairs to the BAHA sound processor were documented on the
subject’s clinical file. These were collated over the full period of the study.
5.3.9 Questionnaire administration
At the pre-operative assessment, two questionnaires were administered to
gauge the subject’s perceived hearing difficulties: the GHABP with the pre-fitting
section, and the APHAB. The subjects were mailed the questionnaire prior to
their appointment to complete with reference to difficulties they were
experiencing with their hearing unaided. Although the APHAB and GHABP
questionnaires were partially completed prior to the initial pre-operative
assessment, responses were discussed as part of the interview process during
the pre-operative assessment.
Those subjects who proceeded with BAHA surgery and fitting were given three
questionnaires post-surgery, including the APHAB, GHABP post-fitting section
and the SSDQ. The SSDQ is shown as Appendix VII. All three questionnaires
were administered at intervals of 3 months, 6 months, 12 months, 18 months, 2
years and 3 years post-fitting of the sound processor. Subjects were
encouraged to write their own comments and reflections under the “Comments”
section of the questionnaires. Testing occurred within two weeks of the set
period whenever possible. The individual centres stored the original versions of
the completed questionnaires and raw data from the speech perception
assessments.
Towards the conclusion of the study the non-implanted subjects (n=35) who
decided not to proceed with rehabilitation with a BAHA implantation were sent
the APHAB and GHABP questionnaires, an extra questionnaire to determine
employment history and if an alternative amplification device were being used
(see Appendix XII), a covering letter and a pre-paid reply envelope. If these
subjects nominated specific hearing difficulties in the GHABP, this data was
87
re-entered by the centre. If a reply was not received after one month, the
subject was contacted by phone and the questionnaires were sent out again if
required.
5.3.10 Data analysis
To guarantee anonymity, Healthy Hearing & Balance Centre subjects were
contacted through the audiologists in their centre. The primary investigator and
the computer programmer were the only team members who had secure access
to all on-line subject files and data from the other participating centre. The ESIA
undertook the data analysis.
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Chapter 6: Results
6.1 Subjects
Fifty-six subjects were recruited during this study and underwent a pre-operative
assessment for BAHA candidacy. Of these subjects, 21 proceeded with surgery
and were fitted with a BAHA: the implanted group. Thirty-five subjects were
assessed for the BAHA but did not proceed with the surgery to have the device
fitted: the non-implanted group. These two groups were examined separately
and also compared to determine a treatment effect. The subjects were also
divided depending on the aetiology of their hearing loss: (i) those who had a
tumour removal causing the UPSHL; (ii) those who acquired UPSHL before the
age of 12 years; (iii) those who acquired UPSHL after the age of 12 years; (iv)
those who had a congenital UPSHL. The implanted and non-implanted groups
had similar distribution of each of these four categories as shown in Figure 6.1.
No significant statistical difference between these groups was found.
0
5
10
15
20
25
30
35
All subjects Implanted subjects Non-implanted subjects
Num
ber o
f sub
ject
s
Tumour
Acquired HL at >12yrs
Acquired HL at <12yrs
Congenital HL
Figure 6.1. Subject group categorisation according to aetiology of hearing loss (HL=hearing loss) (n=56).
89
6.1.1 General subject characteristics
The subjects, comprised of 30 men and 26 women, were recruited for the study
between June 2003 and April 2008. The subjects’ average age and duration of
deafness at the time of the pre-operative assessment was 51.5 years (sd ± 11.1
years, range 28.4 to 73.7 years) and 12.8 years (sd ± 15.9 years, range 0.1 to
62.7 years), respectively. All subjects had a profound sensorineural hearing
loss in the affected ear, as characterised by a mean PTA3F of 114.3 dB HL (sd
± 13.2dB HL). All subjects had normal or near-normal hearing in the non-
affected ear, with a mean PTA3F of 10.4dB HL (sd ± 6.5dB HL). There was no
statistical difference between males and females in the following: their ages,
length of hearing loss, amount of hearing loss in the affected ear, hearing
thresholds in the non-affected ear, or decision to proceed with implantation.
There were three subjects who did not strictly meet the criteria for UPSHL. One
subject had a PTA3F in the non-affected ear of 27dB HL (S21). This subject
had an intermittent conductive overlay in the non-affected ear. However, her
BC thresholds were within normal limits being 20dB HL at 0.5, 1 and 2kHz,
without an air-bone gap, hence her inclusion in the study. There were two
subjects who recorded > 20% SD with AB word lists in their affected ear under
headphones. These subjects, S44 and S51, had recorded 27% and 23% SD
scores, respectively. Examination of the clinical speech masking levels in the
opposite ear for both subjects showed that this level was insufficient, and should
have been at higher levels to ensure effective speech masking levels. One of
these subjects (S44) had acquired his UPSHL from a head injury and therefore
could not tolerate the higher speech masking levels required to effectively mask
his non-affected ear. It is highly likely that his SD scores under headphones
would have been <20% and therefore fitting the criteria if reassessed with the
appropriate levels of clinical speech masking. Despite not meeting one section
of the criteria, because the subjects fitted other criteria sections, such as their
PTA3F, they were included in the study.
As shown in Figure 7.1, 17 subjects had a UPSHL resulting from VS or other
tumour excision (30.3%). Thirty subjects had an acquired unilateral SNHL after
90
12 years of age, seven subjects had an acquired UPSHL before 12 years of
age, and two subjects had a congenital UPSHL. The acquired UPSHL causes
included idiopathic sudden SNHL (25%), mechanical cochlear trauma (14.2%,
from causes such as a bomb explosion, head injury and barb-wire severing the
cochlear nerve) and Meniere’s disease (12.5%). The left ear was the affected
ear in 29 of the cases. There was no significant relationship between the
affected ear and any other factors recorded in this study.
6.1.2 Implanted subject characteristics
Twenty-one subjects (10 men and 11 women) proceeded with BAHA surgery
following their pre-operative evaluation. The average age and duration of
deafness at the time of the pre-operative assessment was 51 years (sd ± 9.5
years, range 30.9 to 68.8 years) and 7.5 years (sd ± 10.5 years, range 0.2 to
39.3 years), respectively as shown in Table 6.1. All subjects had a profound
sensorineural hearing loss in the affected ear, as characterised by a mean
PTA3F of 117 dB HL (sd ± 13.2dB HL). All subjects had normal or near-normal
hearing in the non-affected ear, with a mean PTA3F of 11.4dB HL (sd ± 6.8dB
HL).
Six implanted subjects had a UPSHL resulting from VS or other tumour excision
(28.6%). Thirteen subjects had an acquired UPSHL after 12 years of age. One
subject had an acquired UPSHL before 12 years of age (due to an idiopathic
sudden SNHL at 2 years of age), and one subject had a congenital UPSHL as
shown in Table 6.1. The percentages of the implanted subjects who had
acquired UPSHL causes included idiopathic sudden SNHL (28.6%), Meniere’s
disease (19%)%), mechanical cochlear trauma (14.2%), and otosclerosis
(4.8%).
91
Table 6.1
Implanted subjects’ characteristics (n=21).
Subject Gender
Age at
pre-operative assessment
(y,m)
Duration of deafness at pre-
operative assessment
(y,m)
Cause of hearing loss
Affected ear
S1 M 40,1 3,0 Meniere's disease R
S2 F 46,9 9,6 Mechanical cochlear
trauma
R
S3 M 61,2 0,4 Meniere's disease R
S4 M 55,1 6,5 Meniere's disease R
S5 F 54,9 0,7 Idiopathic sudden
SHNL
R
S6 F 53,5 23,3 Idiopathic sudden
SNHL
R
S7 F 58,7 1,4 VS surgery R
S8 M 60,4 9,6 VS surgery R
S9 F 56,3 1,1 VS surgery L
S10 M 64,3 0,4 VS surgery L
S11 M 50,7 0,8 VS surgery R
S12 F 44,1 10,9 Trigeminal
schwannoma
L
S13 M 44,7 5,3 Idiopathic sudden
SNHL
L
S14 F 68,8 2,0 Idiopathic sudden
SNHL
L
S15 F 39,3 39,3 Congenital L
S16 M 30,9 28,9 Idiopathic sudden
SNHL
R
S17 F 49,8 1,9 Idiopathic sudden
SNHL
L
S18 F 40,1 0,9 Mechanical cochlear
trauma
L
S19 M 44,8 8,6 Otosclerosis L
S20 M 58,5 0,2 Meniere's disease L
S21 F 47,3 2,9 Mechanical cochlear
trauma
R
VS= Vestibular schwannoma; L = left; R = right; M = male; F = female; y,m = year, month
SNHL = sensorineural hearing loss
92
6.1.3 Non-implanted subject characteristics
Thirty-five subjects (20 men and 15 women) chose not to proceed with
implantation after pre-operative evaluation for BAHA candidacy. This subject
group’s average age and duration of deafness at the time of the pre-operative
assessment was 51.8 years (sd ± 12 years, range 28.4 to 73.7 years) and 16
years (sd ± 17.7 years, range 0.1 to 62.7 years), respectively.
All subjects had a profound sensorineural hearing loss in the affected ear as
characterised by a mean PTA3F of 112.7 dB HL (sd ± 13.1dB HL). All subjects
had normal or near-normal hearing in the non-affected ear, with a mean PTA3F
of 9.8dB HL (sd ± 6.3dB HL). Eleven subjects had a UPSHL resulting from VS
or other tumour excision (31.4%). Sixteen subjects had an acquired UPSHL
after 12 years of age; six subjects had an acquired UPSHL before 12 years of
age; and one subject had a congenital UPSHL as shown in Figure 7.1. The
percentages of the implanted subjects who had acquired UPSHL causes were
from idiopathic sudden SNHL (28.6%), mechanical cochlear trauma (17%),
Meniere’s disease (8.6%), progressive hearing loss (8.6%), and other causes
(2.9%). The affected ear was the left ear in 18 of the cases as shown in Table
6.2.
93
Table 6.2 Non-implanted subject characteristics (n=35).
Subject Gender
Age at
pre-operative assessment
(y,m)
Duration of profound levels at
pre-operative assessment
(y,m)
Cause of hearing loss
Affected ear
S22 M 63,9 10,0 Idiopathic progressive SNHL L
S23 F 44,2 20,9 Idiopathic sudden SNHL R
S24 F 66,2 49,2 Idiopathic progressive SNHL L
S25 M 60,7 51 Mechanical cochlear trauma R
S26 M 28,4 2,4 Mechanical cochlear trauma L
S27 M 54,0 44,0 Idiopathic sudden SNHL L
S28 M 48,7 48,7 Congenital R
S29 M 57,1 41,1 Idiopathic sudden SNHL R
S30 F 41,5 0,3 Meniere's disease R
S31 M 50,5 0,5 VS surgery L
S32 M 60,3 2,9 VS surgery L
S33 F 65,3 2,8 VS surgery R
S34 F 43,6 1,9 Idiopathic sudden SNHL L
S35 M 44,2 16,7 VS surgery L
S36 M 59,4 6,5 Mechanical cochlear trauma L
S37 M 49,9 1,4 Brain lesions L
S38 M 59,2 24,1 VS surgery L
94
Table 6.2 continued
Subject Gender
Age at
pre-operative assessment
Duration of profound levels at pre-operative
assessment Cause of hearing loss
Affected ear
S39 M 45,2 10,3 Systemic disorder (hypereosinophilia) R
S40 M 50,3 45,3 Idiopathic sudden SNHL L
S41 M 42,9 0,1 Idiopathic progressive SNHL L
S42 F 55,4 4,0 VS surgery R
S43 M 62,2 4,1 Intra cochlear schwannoma L
S44 M 31,5 2,3 Mechanical cochlear trauma R
S45 F 38,8 2,6 VS surgery L
S46 F 37,5 19,7 Meniere's disease R
S47 F 32,7 28,7 Idiopathic sudden SNHL R
S48 F 29,9 29,1 Idiopathic sudden SNHL R
S49 F 41,7 33,7 Idiopathic sudden SNHL R
S50 F 57,8 0,7 Mechanical cochlear trauma R
S51 F 64,2 62,7 Idiopathic sudden SNHL L
S52 M 71,0 1,2 Mechanical cochlear trauma L
S53 F 73,7 15,3 VS surgery R
S54 M 62,4 9,8 Idiopathic sudden SNHL L
S55 M 56,8 10,5 Meniere's disease R
S56 F 61,2 2,0 VS surgery L
VS = Vestibular schwannoma; HL-= hearing loss; L = left; R = right; M = male; F = female; y,m = year, month; SNHL = sensorineural hearing loss
95
The PTA3F of each of the subjects’ affected and non-affected ear is shown in
Figure 6.2.
0 10 20 30 40 50 60 70 80 90 100 110 120 130
123456789
101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657
Subj
ect n
umbe
r
dB HL
Non-affectedearAffectedear
Figure 6.2. Individual subject’s PTA3F in each ear (n=56).
6.1.4 Subject implantation and BAHA device
Within the group of implanted subjects, 10 had left-sided implants, and 11 had
right-sided implants. Table 6.3 shows details of the surgery, fitting age of the
subjects and the devices fitted. The implanted group’s mean average age at
the time of the surgery was 51.3 years (sd ± 9.3 years, range 32.9 to 68.9
years), and the BAHA sound processor was fitted an average of two months
post-surgery as shown in Table 6.3. The most recently fitted implanted subject
96
in the study was subject (S17), who was fitted with her sound processor in
February 2008. Subject, S8 has been the longest BAHA user having been fitted
in April 2004.
The subjects adjusted the BAHA volume to their preferred level for everyday
use. There was little variance between subjects’ preferred level of volume with
the range being from 1.5 to 2.5 in both ear level models of speech processors.
Table 6.3
Implanted subjects’ surgery and device details (n=21).
Subject
Age at surgery
Fitting Age
Model Device
upgraded S1 40.3 40.5 Compact No S2 47.1 47.3 Compact No S3 61.3 61.5 Compact Yes S4 55.1 55.3 Compact No S5 55.0 55.2 Compact No S6 53.6 53.8 Compact No S7 58.8 59.0 Compact No S8 61.0 61.2 Compact Yes S9 56.5 56.7 Compact No
S10 64.5 64.7 Compact No S11 52.3 52.5 Divino No S12 44.2 44.5 Divino No S13 45.3 45.5 Divino No S14 68.9 69.1 Divino No S15 39.5 39.7 Compact Yes S16 32.9 33.1 Divino No S17 50.1 50.3 Divino No S18 40.2 40.4 Compact Yes S19 45.0 45.2 Compact No S20 58.7 58.9 Compact No S21 47.6 47.8 Compact No
97
6.2 Speech testing in quiet via free-field testing
There were three different test protocols used for speech testing. The subjects
were placed into one of the three groups depending on the time of their pre-
operative assessment. The groups were (i) Group A: fixed presentation level of
40 dB HL; (ii) Group B: SNR changes of 2 dB whilst scoring between 40% and
60% correct, and (iii) Group C: SNR changes of 1 dB whilst scoring between
48% and 52% correct. Due to small subject numbers, Group B and Group C
speech discrimination scores were combined and presented as Group B/C.
6.2.1 Pre-operative speech results of Group A
Eighteen subjects were assessed using a fixed presentation level of 40 dB HL.
The range of percentage scores correct at 40 dB HL was from 27% to 83% for
the 18 subjects as shown in Figure 6.3. Subject’s test band advantage was
calculated by subtracting the average percentage correct score obtained from
when unaided from the average percentage correct score when wearing the
BAHA on the test band. The mean test band advantage for this group was
14%. Group A’s pre-operative testing results were also divided into subjects
who were implanted and those who were not non-implanted. The implanted
subjects’ average test band advantage was 16% (n=11), while the non-
implanted group’s average test band advantage was 11% (n=7).
0102030405060708090
S1
S2
S7
S8
S10
S11
S15
S18
S19
S20
S21
S22
S24
S25
S28
S33
S51
S52
Ave
rage
Subject
Perc
enta
ge c
orre
ct %
Test band Unaided
Figure 6.3. Group A free-field speech testing in quiet using AB words (n=18).
98
6.2.2 Pre-operative speech results of Group B/C
Twenty-four subjects’ speech discrimination was assessed using the Group B or
C test protocols. When combining the Group B and C results, this was
represented as Group B/C. Twenty (83.3%) of the subjects scored between
40% and 60% correct when tested with either the BAHA on a test band or
unaided at the same presentation level in both conditions in quiet. However,
four (16.4%) subjects (S14, S30, S31 and S32) showed a significant difference
in presentation level between the aided and test band conditions. The
presentation level range was between +4dB dB HL and -4dB dB HL. Three of
these four subjects achieved the percentage correct score at lower presentation
levels with the test band than in the unaided condition, whereas the fourth
subject (S31) required the presentation level to be louder for the test band than
in the unaided condition. The average presentation level that was required to
achieve the percentage range of test band correct scores was 27 dB HL as
shown in Figure 6.4. The average for the implanted group was 23 dB HL (n=4)
and the non-implanted group was 27.6 dB (n=20).
99
0
5
10
15
20
25
30
35
40
45
S12
S13
S14
S16
S27
S29
S30
S31
S32
S34
S35
S37
S38
S40
S41
S42
S43
S44
S45
S48
S49
S53
S54
S56
Aver
age
Pres
enta
tion
leve
l
Test band/unaided Unaided Test band
Figure 6.4. Group B/C presentation levels (dB HL) for AB words in quiet tested in the free-field (n=24).
NB: Separate test band and unaided scores are shown when there was a significant difference in presentation levels. Overall test band average is shown. The subjects' scores which did not change between test band and unaided are depicted in light purple.
6.2.3 Post-operative results of Group A
Seven of the subjects in Group A who proceeded with implantation were
assessed post-operatively to determine if the advantage in speech scores with
the BAHA implanted corresponded to the advantage in speech scores prior to
surgery with the BAHA on the test band. Four subjects (S2, S7, S10 and S15)
were not assessed post-operatively due to time constraints during their
appointment. The mean BAHA advantage percentage for the group was 20%.
Post-operatively, the mean of the implanted subjects’ scores was 1% higher
with their BAHA compared to the BAHA on the test band advantage scores as
shown in Figure 6.5. One subject (S20) showed no difference in his BAHA
advantage post-operatively scoring. This is not shown in Figure 6.5 as it is level
with the axis.
100
-10
0
10
20
30
40
50
S1
S8
S11
S18
S19
S20
*
S21
Ave
rage
Subject
Perc
enta
ge c
orre
ct %
Test band advantage (% correct) BAHA advantage %
Figure 6.5. Pre- and post-operative AB words in quiet scores tested in the free-field (n=7).
NB: The BAHA advantage percentage for S20 was 0dB HL.
The Wilcoxon Signed Ranks test was used to determine if the use of a BAHA
either on a test band or implanted (the treatment), had an effect on speech
discrimination in quiet as measured by AB words conducted in the free-field,
and whether there was a difference between the test band BAHA and implanted
BAHA scores. The analysis showed that there was a significant outcome from
the treatment, both for the use of a BAHA on a test band and also the BAHA
post-operatively as shown in Table 6.4. As could be expected, there was no
significant difference between the unaided test results pre- and post-operatively.
These results indicate that there was a treatment effect from the use of the
BAHA on speech perception in quiet.
101
Table 6.4 Group A intra-subject scores for AB words Wilcoxon Signed Rank Test for test
band, BAHA and unaided pairs (n=7).
Pair of conditions Z Asymp. Sig. (2-tailed) Pre-operative test band Pre-operative unaided
-2.472 0.013*
Post-operative BAHA Post-operative unaided
-2.207 0.027*
Pre-operative test band Post-operative BAHA
-2.201 0.027*
Pre-operative unaided Post-operative unaided
-1.214 0.225 ns1
* indicates significant difference (p<0.05); ns - not significant.
6.2.4 Post-operative results of Group B/C
Only two subjects in Group B were tested post-operatively. The presentation
level used for speech testing was the subject’s level that was achieved
pre-operatively. One subject (S13) achieved the same percentage correct with
the implanted BAHA as he did with the test band BAHA when using this
presentation level, so there was no change in performance post-operatively.
The other subject (S16) achieved the pre-operative scores at the presentation
level of 8 dB HL but when retested at this level post-operatively, this subject
only achieved 20% correct with the BAHA device. The subject was unable to
respond to the presentation level in the unaided condition, scoring 0% correct.
Group C did not have any implanted subjects that were retested post-
operatively. Therefore the results from this cohort of subjects are inconclusive.
6.3 Speech testing in noise
6.3.1 Pre-operative results of Group A
Group A consisted of 24 subjects’ results as it included those who did not
proceed with implantation. Pre-operative speech testing in noise was
conducted with the noise coming from three directions. Speech was presented
in all three conditions from a free-field speaker directly in front of the subject.
As these subjects were tested at a fixed SNR, the difference between their
percentage correct score when wearing the BAHA on a test band minus their
unaided percentage correct was calculated. This was recorded as test band
SNR dB advantage. The data on 10 subjects with pre- operative testing with
102
the BAHA on the test band and unaided scores were normalised for the test
band BAHA on the right side for the analysis. The analysis, using the Wilcoxon
Signed Ranks test aimed to determine whether there was a BAHA on the test
band treatment effect dependent on the direction of the noise.
As indicated in Table 6.5, the analysis showed that there was no significant
treatment effect from using the BAHA on the test band for any of the three noise
conditions.
Table 6.5 BKB/A sentence results for Group A using Wilcoxon Signed Ranks Test (n=10).
Pair of conditions Z Asymp. Sig. (2-tailed)
Pre-operative S0:N270 test band- Pre-operative S0:N270 unaided
-1.315
0.188 ns
Pre-operative S0:N90 test band - Pre-operative S0:N90 unaided
-0.511 0.609 ns
Pre-operative S0:N0 test band - Pre-operative S0:N0 unaided
-0.356 0.721 ns
* indicates significant difference (p<0.05); ns - not significant.
6.3.2 Pre-operative results of Group B/C
Thirty-two subjects in Groups B/C undertook pre-operative testing. Of this
number, only five subjects achieved a score between 40% to 60% in all three
noise conditions. Data from the other subjects could not be used, as the
required scores were not achieved. The SNR dB for the five subjects was the
same for both the test band BAHA and the unaided condition as shown in
Figure 6.6. One subject (S49) had a BKB/A SNR that differed between the test
band BAHA and unaided condition when the noise was presented from the left
and right (i.e. S0:N270 and S0:N90). A 2 dB SNR test band advantage was
seen in the S0:N270 condition, and a 1 dB SNR test band advantage in the
S0:N90 condition. A SNR of 0 was seen in the S0:N270 condition.
103
-12
-10
-8
-6
-4
-2
0
2
4
6
S17 S29 S42 S49* S55
Subjects
dB H
L Pre S0:N270Pre S0:N90Pre S0:N0
Figure 6.6. Group B/C pre-operative BKB/A SNR levels (n=5).
NB: The SNR for S49 in the pre-operative S0:N270 was 0dB SPL.
Within the Group B/C, 11 subjects’ test results fitted the criteria of scoring 40%
to 60% correct when tested in the S0:N270 condition. In the S0:N90 condition,
18 subjects’ test results fitted the criteria, while 24 subjects fitted the criteria in
condition S0:N0. With these results, only inter-subject comparisons can be
made, not intra-subject comparisons. In the S0:N270 condition, subjects scored
0.20 dB SNR better with the test band than in the unaided condition (a test band
advantage was found). In the S0:N90 condition, subjects scored a 0.36 dB
SNR test band advantage, and in the final noise condition S0:N0, a 0.08 dB
SNR test band advantage was detected.
6.3.3 Post-operative results of Group A
Ten subjects in Group A were assessed post-operatively. Subjects were
assessed with the same fixed SNR level in all three test conditions (S0:N0,
S0:N270 and S0:N90). A Wilcoxon Signed Ranks test was used to compare
pre-operative test band results with post-operative BAHA scores in noise as
shown in Table 6.6. The analysis showed that there was no significant
difference between the BAHA and the unaided condition in all three noise
conditions. In addition, Table 6.6 shows that further analysis using the
104
Wilcoxon Signed Ranks test showed no significant difference between the pre-
operative test band results and the BAHA results post-operatively.
Table 6.6 Group A subjects’ post-operative scores for BKB/A sentences using Wilcoxon Signed Ranks Test. n=10).
Pair of conditions Z Asymp. Sig. (2-tailed)Post-operative S0:N270 BAHA Post-operative S0:N270 unaided
-0.102 0.918 ns
Post-operative S0:N90 BAHA Post-operative S0:N90 unaided
-0.339 0.734 ns
Post-operative S0:N0 BAHA Post-operative S0:N0 unaided
-0.654 0.513 ns
Pre-operative S0:N270 test band Post-operative S0:N270 BAHA
-0.509 0.610 ns
Pre-operative S0:N90 test band Post-operative S0:N90 BAHA
-0.280 0.779 ns
Pre-operative S0:N0 test band Post-operative S0:N0 BAHA
-1/126 0.260 ns
* indicates significant difference (p<0.05); ns - not significant.
6.3.4 Post-operative results of Group B/C
Four implanted subjects in Group B/C were tested in the three noise conditions.
Results showed that the range of SNR was from -8dB to +5dB in 1-2 dB
increments in order to achieve an approximate percent correct score of 40% to
60% using an adaptive procedure. The affected ear results were normalised to
the right side for the analysis. Results showed that over time, one subject (S14)
was able to achieve between 40% and 60% correct at a SNR level with greater
difficulty post-operatively compared to pre-operative SNR levels. For example,
the subject needed a +5 dB SNR to achieve this criterion in the S0:N270 pre-
operative condition, but was able to achieve the same result at -3.5 dB SNR at
2 years post-fitting with the BAHA device. Overall results indicated a trend
towards a reduction in the SNR once the subject was implanted.
As there were only four subjects, results can only be viewed as a trend, as
shown in Figure 6.7. Subject 14 had a pre-operative SNR of 0 dB in the S0:N0
condition as indicated by an asterisk in Figure 6.7.
105
-10
-8
-6
-4
-2
0
2
4
6
Pre0:270
Pre0:90
Pre 0:0 Post0:270
Post0:90
Post0:0
Post0:270
Post0:90
Post0:0
Pre-operative Short-term Long-term
Subject
SNR
S13 L
S17 L
S16 R
S14* L
Figure 6.7. Group B/C’s SNR levels using BKB/A sentences (n=4).
NB: S14 scored 0dB SNR in the pre-operative S0:N0 condition.
6.4 Abutment and repair issues
Both surgical and audiological clinical notes and reports of the 21 implanted
subjects were reviewed to ascertain the number of post-surgical complications
and general use of the BAHA devices. Table 6.7 shows the incidence and
treatment of the skin infections of the implanted subjects within the study.
There were several subjects who had more than one skin reaction. The time
frame after BAHA surgery was noted. Eight subjects had skin issues around
the abutment. There were seven subjects whose skin infections required
topical treatment with antibiotic cream, two subjects who required revision
surgery, and another subject who needed revision surgery but decided not to
proceed.
106
Table 6.7
Subjects who had skin reactions requiring treatment (n=8).
Subject Type of skin reaction Occurrence after BAHA
surgery (y;m)
Treatment
S2
Infection around abutment; swab showed Staphylococcus aureus.
0;1 Bactroban ointment and oral antibiotics (Augmentin).
S7
Minor granulation tissue around abutment.
0;5 Kenacomb ointment prescribed.
S8
Abutment completely covered by healed skin.
1;1 Revision surgery, wound flap repair and removal of soft tissue.
S11
Marked skin growth around abutment, hypertrophic skin causing inflammation and bleeding.
0;9 Subject required revision skin surgery, but did not want to proceed. Kenacomb ointment prescribed.
S12
Minor skin reaction. Infection and irritation around abutment. Swab showed Staphylococcus aureus.
0;1 1;4
Kenacomb ointment prescribed. Oral antibiotics prescribed.
S13
Residual amount of crusting. Residual amount of crusting.
0;1 1;0
Kenacomb ointment prescribed. Kenacomb ointment prescribed.
S18
Unhealed skin. Unhealed skin.
0;5 0;7 0;8
1;3
Topical and oral antibiotics. Topical and oral antibiotics. Surgery for minor wound breakdown; excision of necrotic skin and partial thickness of skin graft due to poor blood supply from previous surgery. Splint skin graft and reinsertion of BAHA abutment.
S19
Infection and granulation tissue around abutment.
3;3 Kenacomb ointment; cauterised the granulation tissue. Recommended GP assessment; and topical silver nitrate and Kenacomb ointment treatment.
GP= General Practitioner
Three of the subjects had their abutment removed, two permanently (S1 and
S12). The third subject (S18) had the abutment repositioned due to poor blood
supply at its previous location. Two subjects underwent revision surgery around
their abutment. Subject eight’s surgery was due to excess skin growth, while
the other subject (S18) required revision surgery due to partial thickness of skin
graft and as part of staged surgery to reposition the abutment.
107
Fourteen subjects (66.7%) had their external sound processors repaired by the
manufacturer as shown in Table 6.8. The mean number of repairs required by
each subject was 1.93 (range 1-5).
Table 6.8
Subjects’ surgical and repair issues (n=21).
Post-operative complications
Number of subjects
% of subjects
Skin reactions 8 38.0 Revision surgery 2 9.5 Abutment removed 3 14.3 Repairs required (total) 27 Repairs required (subjects) 14 66.7 Repairs (average for all subjects) 1.29 Repairs (average for subjects with repairs) 1.93
The majority of the reported faults were due to the collapse of the air gap
between the two magnets within the transducer, as shown in Figure 6.8.
Figure 6.8. Schematic drawing of the internal components of the BAHA.
(1) Skull bone (2) Skin and subcutaneous tissue and cells and skin (3) Implanted titanium fixture (4) Titanium abutment (Chalmers University of Technology, Goteborg, Sweden). Note. From (Hakansson, 2006).
108
There were four implanted subjects who stopped wearing their BAHA device
between 1.2 to 3.5 years post-fitting. Two of these non-users had their
abutment surgically removed. Three of the subjects reported that they stopped
wearing the device due to limited power and/or benefit. One subject (S12) had
stopped using the device due to pain from the abutment and consequently had
the abutment removed. Despite incidences of post-operative complications and
faults with the BAHA device, 17 subjects (81%) were still wearing their BAHA
device as shown in Table 6.9. The average length of usage was three years
and two months post-fitting of the sound processor.
Table 6.9 BAHA usage, post-operative complications and repairs of the implanted subjects (n=21).
Subject Post-op skin reactions
Repairs to device
Non-surgical issues
Abutment removal
Length worn BAHA device (years)
Wearing device
S1 N Y N 26/02/2007 2.4 N S2 Y N Y N 3.9 Y S3 N Y N N 4.6 Y S4 N Y N N 3.1 Y S5 N Y N N 4.1 Y S6 N Y N N 3.3 Y S7 Y Y N N 2.6 N S8 Y N N N 4.6 Y S9 N Y N N 4.5 Y S10 N Y Y N 3.5 N S11 Y Y Y N 2.5 Y S12 Y Y Y 12/06/2008 1.2 N S13 Y Y N N 1.9 Y S14 N Y N N 2.4 Y S15 N Y N N 4.0 Y S16 Y N N N 0.8 Y S17 N N N N 1.1 Y S18 Y Y Y Y (replaced) 4.4 Y S19 Y N N N 3.9 Y S20 N N N N 4.2 Y S21 N N N N 4.5 Y
109
6.5 Questionnaires
6.5.1 Implanted subjects APHAB results
The APHAB was readministered several times to each implanted subject (over
a three year period for some subjects). A Wilcoxon Signed Ranks Test was
used to determine if use of a BAHA (the treatment) had an effect on the quality
of life (QOL) as measured by the APHAB questionnaire. The pre-operative
results were compared to initial short-term (3-12 months) post-operative results
(n=16) and also to the long-term (between 12-36 months) post-operative results
(n=18). There were several subjects who did not have completed APHAB
results either by absence of a pre-operative response or post-operative
response. Therefore there were 16 subjects’ results for the short-term analysis,
while there were 18 subjects’ results in the long-term analysis.
The analysis showed that there was significant improvement in the average
APHAB score and subscales in the short-term after surgery as shown in Table
6.10. Although there was long-term improvement in the average and across all
the subscales, a significant improvement was only seen for the average APHAB
score and the BN and RV subscale scores. These results suggest that there is
a significant long-term treatment effect of the BAHA on QOL as assessed by the
APHAB, although in some situations the advantage is not as great as in the
initial post-operative period.
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Table 6.10 Implanted subjects’ APHAB results using Wilcoxon Signed Ranks Test (n=16 unless indicated otherwise).
6.5.2 Non-implanted subjects – APHAB results from initial and repeated surveys
In order to examine the QOL of subjects that were assessed for a BAHA but
were not implanted, the APHAB questionnaire was readministered. The
average time after the initial administration of the questionnaire was 2 years, 7
months (range of time varied from 6 months to 4 years, 7 months). A total of 22
of the 35 subjects who were initially surveyed responded to the request to
repeat the survey (63% response rate). Wilcoxon Signed Ranks Test showed
no significant difference in scores over time (no ‘treatment’ effect of being not
implanted) as shown in Table 6.11. The spread of results was greater the
second time the survey was completed.
Pair of conditions Z Asymp. Significance (2-tailed)
APHAB Pre average – APHAB short term post average -3.413
0.001 *
APHAB Pre EC – APHAB short-term post EC -3.258
0.001 *
APHAB Pre BN – APHAB short-term post BN -3.258
0.001 *
APHAB Pre RV – APHAB short-term post RV -3.361
0.001 *
APHAB Pre AV – APHAB short-term post AV -1.931
0.053 ns
APHAB Pre average – APHAB long-term post average -3.206
0.001 *
APHAB Pre EC – APHAB long-term post EC -1.758
0.079 .ns
APHAB Pre BN – APHAB long-term post BN -2.840
0.005 *
APHAB Pre RV – APHAB long-term post RV -2.844 0.004 * APHAB Pre AV – APHAB long-term post AV -0.738
0.460 ns
APHAB short-term post average – APHAB long-term post average
-2.668 (n=18)
0.008 *
APHAB short-term post EC – APHAB long-term post EC -2.097 (n=18)
0.036 *
APHAB short-term post BN – APHAB long-term post BN -2.417 (n=18)
0.016 *
APHAB short-term post RV – APHAB long-term post RV -1.224 (n=18)
0.221 ns
APHAB short-term post AV – APHAB long-term post AV -0.863 (n=18) 0.388 ns * indicates significant difference (p<0.05); ns - not significant.
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The second administration of the APHAB to the 22 subjects who were not
implanted showed no significant change in their pre-operative subscale scores
when compared to their second set of subscale scores, although there was a
large spread of the scores as indicated by the large standard deviations. Over
the time since their pre-operative assessment, these 22 subjects as a group did
not have a significant change in their subjective hearing disability, although the
standard deviation was great (ranging from 9.88 (EC) to 19.56 (RV) across the
four subscales).
Table 6.11 Non-implanted subjects’ APHAB results using Wilcoxon Signed Ranks Test (n=22).
Pair of conditions Z Asymp. Sig. (2-tailed)
1st response Average -
2nd response Average 0.000 1.000 ns
1st response EC subscale -
2nd response EC subscale -0.414 0.679 ns
1st response BN subscale -
2nd response BN subscale -0.762 0.446 ns
1st response RV subscale -
2nd response RV subscale -0.563 0.573 ns
1st response AV subscale -
2nd response AV subscale -0.261 0.794 ns
* indicates significant difference (p<0.05); ns - not significant.
6.5.3 Implanted subject GHABP results
The post-operative residual disability scale score should be lower to indicate
improvement and decreased disability, whereas for the other scales,
(satisfaction, benefit, and use), the higher scores indicate better post-operative
results in these scales.
The Wilcoxon Signed Ranks Test was used to determine if the use of a BAHA
(the treatment) had an effect on the quality of life as measured by the GHABP
questionnaire. The pre-operative results were compared to initial short-term
post-operative results (n=17) and also to the long-term results (n=19) as shown
in Table 6.12. The analysis showed that there was a significant improvement in
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the disability scores – pre-operative initial disability to short-term and long-term
post-operative residual disability scores. There was a significant improvement
between short-term and long-term use, benefit, and satisfaction scale scores.
These indicate that there was increased treatment effect over time.
Table 6.12 Implanted subjects’ GHABP results using Wilcoxon Signed Ranks Test (n=19 unless indicated otherwise)
Pair of conditions Z Asymptotic Significance
(2-tailed) Pre-operative initial disability scale Short-term post-operative residual disability scale
-3.338 (n=17) *0.001
Pre-operative initial disability scale Long-term post-operative residual disability scale
-3.312 (n=17) *0.001
Short-term post-operative use scale Long-term post-operative use scale
-2.401 *0.016
Short-term post-operative benefit scale Long-term post-operative benefit scale
-2.357 *0.018
Short term post-operative residual disability scale Long-term post-operative residual disability scale
-1.836 0.066n.s.
Short –term post-operative satisfaction scale Long-term post-operative satisfaction scale
-2.580 *0.01
* indicates significant difference (p<0.05); ns - not significant.
6.5.4 Non-implanted subjects – GHABP results from initial and repeated surveys
The non-implanted subjects were sent the GHABP with their previously
nominated areas of difficulties included on the questionnaire. Data for one of
the non-implanted subjects was not available due to non-compliance. A total of
34 subjects were sent the GHABP survey (along with the APHAB survey), and
21 responded (62% response rate). The questionnaires were posted out an
average of 2 years, 6 months after the pre-operative assessment (range: 6
months to 4 years, 7 months). The Wilcoxon Signed Ranks Test (see Table
6.13) indicated a statistically insignificant decrease in the level of disability and
handicap scale over time.
Table 6.13
Non-implanted subjects’ GHABP responses using paired samples t-test (n=21). Pair of conditions Z Asymp. Sig. (2-tailed) Initial Disability Scale 1st response Initial Disability Scale 2nd response
-0.112
0.911 ns
Handicap Scale 1st response Handicap Scale 2ndresponse
-1.808 0.071 ns
* indicates significant difference (p<0.05); ns - not significant.
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6.5.5 Alternative aids and employment
The second set of questionnaires sent to the non-implanted subjects included a
questionnaire examining whether they were wearing an alternative hearing aid
or hearing system to that of a BAHA, and whether the person was working (see
Appendix XII). All subjects who responded indicated that they were not wearing
any amplification device, except one subject (S45) who had been fitted with a
WiFi CROS system since the BAHA assessment. The average age of the non-
implanted respondents was 54.1 years at the time of the second survey. When
asked if they were in employment, 31.8% (7/22) responded that they were not
working. The average age of those not working was 60.9 years, with four out of
the seven individuals’ age greater than the retirement age of 65 years.
A lower percentage of the implanted subject group, 14.3% (3/21) were recorded
as not working, as indicated in their audiology files. The average age of the
implanted subjects who were not working was 63.9 years. Two of the three
implanted subjects (S7 and S10) who were not working had also stopped using
their BAHA.
6.5.6 SSDQ
The SSDQ was administered to the implanted subjects post-operatively. The
subjects’ results were divided into short-term (3-6 months) and long-term (12 to
36 months) outcomes. The short-term SSDQ results showed that implanted
subjects (n=18) rated their satisfaction with the device with an average score of
7.8 out of 10 (with 10 being “very satisfied” on the scale). With the same
scoring system, they rated the aesthetics of the device with an average of 8.4
out of 10. In question 3, the impact of the fitting of a BAHA on the subjects’
QOL was examined. Seventy-two percent of the subjects responded that it had
improved their quality of life. Six subjects (33%) reported an inability to localise
sound, with another seven (39%) reporting uncertainty as to whether they could
determine where a sound originated while wearing the BAHA. Over 94% of the
subjects found the handling of the device to be “easy” or “very easy”.
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Long-term responses (n=13) showed an increase in the satisfaction rating for
the BAHA, but a lower rating for the aesthetics of the device, when compared to
short-term outcomes. The long-term responses for being able to localise sound
and the benefit from listening to music and hearing the television, showed a
reduction in satisfaction compared with the short-term responses. In the area of
localisation, none of the subjects thought they could localise sound, whereas, in
the short-term responses, three subjects indicated that they could localise
sound when wearing their BAHA. Despite the decreased benefits observed in
some areas over time, the overall responses indicated that subjects continued
to find their BAHA device to be beneficial and improved their quality of life as
shown in Table 6.14.
Further analysis using Wilcoxon Signed Ranks Test showed no significant
change in the SSDQ responses between short-term and long-term in the areas
of number of days the device was used, daily hours of use, quality of life,
satisfaction, aesthetics, or ease of use as shown in Table 6.15.
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Table 6.14
Short-term and long-term SSDQ results from implanted subjects (n=18 unless
otherwise indicated).
Question number
Question Possible responses
Short-term responses of subjects
Long-term responses of
subjects (n=13)
n % n %1 How many days per 7 days/week 6 33 5 38.5 week do you use 5-6 days/week 11 61 6 46.2 your device? 3-4 days/week 1 6 2 15.4
2 How many hours More than 8 10 55 5 38.5 per day do you Between 4-8 7 39 7 53.8 use your device? Between 2-4 1 6 1 7.7
3 Has your quality of Yes 13 72 9 69.2 life improved? No 1 6 0 0 Mixed (Yes and
No) 4 22 4 30.8
4 Try to determine your satisfaction…
Average score 7.8 8.5
(10 point rating scale) Range 6 to 10 6 to 10 5.1 Talking to one Better 15 83 10 76.9
person in a quiet No difference 3 17 2 15.4 situation Worse 0 0 1 7.7
5.2 Talking to one Better 15 83 8 61.5 person among a No difference 3 17 3 23.1 group? Worse 0 0 2 15.4
5.3 Listening to music? Better 13 72 6 46.2 No difference 5 28 3 23.1 Worse 0 0 4 30.8
5.4 Listening to Better 14 78 7 53.8 TV/radio? No difference 4 22 3 23.1 Worse 0 0 2 15.4 Result missing 1 7.7
5.5 At the dinner table? Better 16 88 9 69.2 No difference 1 6 0 0 Worse 0 0 4 30.8 Result missing 1 6
6 Locating where a Yes 3 16 0 0 sound is coming No 6 33 8 61.5 from? Mixed (Yes and
No) 7 39 4 30.8
No difference 1 6 1 7.7 Result missing 1 6
7 How satisfied are you with the aesthetics?
8.4 7.2
(10 point rating scale) Range 4 to 10 5 to 10 8 How do you find the Very easy 7 39 5 38.5 handling of the Easy 10 55 6 46.2 device? Acceptable 1 6 2 15.4
Adapted from Wazen et al. (2003). ^Full questionnaire appears in Appendix VII; n (%)= percentage of subject responses
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Table 6.15
Implanted subjects’ SSDQ responses using Wilcoxon Signed Ranks Test (n=18
unless indicted otherwise)
Pair of conditions Z Asymp. Sig. (2-tailed) Short –term days used Long-term days used
-0.816 0.414 ns
Short-term daily hours used Long-term daily hours used
-0.271 0.786 ns
Short-term QOL Long-term QOL
-0.577 0.654 ns
Short-term satisfaction Long-term satisfaction
-1.000 (n=13) 0.317 ns
Short-term aesthetics Long-term aesthetics
-1.725 (n=13) 0.084 ns
Short-term ease of use Long-term ease of use
-0.577 0.564 ns
* indicates significant difference (p<0.05); ns - not significant; Quality of life
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Chapter 7: Discussion The major findings of this study were there was an improvement in several
subjects’ speech discrimination in quiet with the test band pre-operatively and
post-operatively with the BAHA compared to the unaided condition. There was
no improvement in the subject’s speech discrimination in noise, however there
was limited data due to changes in the test procedures during the study.
Overall the implanted subjects reported improvements in their hearing
difficulties across all three questionnaires compared to their pre-operative
scores when they were unaided. The initial improvement was greater in the
short-term than the long-term across the three surveys, but this reduction in
benefit was not statistically significant.
There were a number of infections and repairs for the implanted subjects as a
group. There were four subjects who ceased wearing their BAHA during the
course of the study. The reasons for discontinuing use of their device did not
appear to be related to repairs or medical reasons in the majority of these
subjects, but rather due to overall lack of reported benefit by the subjects.
Those subjects who were not implanted did not report a change in their self-
reported hearing difficulties in the long-term.
7.1 Subjects
7.1.1 Subject selection
At the onset of this study it was initially decided to recruit subjects from a cohort
of individuals with a UPSHL from VS or skull base surgery. However, as the
number of these individuals willing to undergo surgery was limited, the selection
criterion of the subjects in the study was widened to include subjects with an
acquired UPSHL from other causes. McLeod et al. (2008) reported that post-
surgery VS subjects and subjects with a unilateral severe to profound
sensorineural hearing impairment rated themselves similarly on their disability
level for various hearing situations when compared to subjects with normal
hearing. As shown in the results section, there was a significant correlation for
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certain measures between the group who had a tumour removed and those
subjects who had acquired their hearing loss after the age of 12 years. When
pre-operative questionnaire responses from the two groups were examined, it
was apparent that their areas of hearing difficulties were very similar.
Therefore, subjects with a UPSHL from various aetiologies such as Meniere’s
disease, viral infections and cochlear trauma were included as the profile of
their associated problems with their hearing loss were similar to those who had
acquired a UPSHL from VS or skull base surgery.
The implanted and non-implanted subject groups were not matched for age and
gender; this was subject to the decision of the subject and their suitability for a
BAHA. However, there was no significant difference between the age at
assessment or affected ear side for the implanted and non-implanted groups.
There was no significant difference in the length of profound hearing loss
between the groups despite the implanted subject group having shorter period
of profound level of hearing loss (average was seven years) than those who
were not implanted (average was 16 years). The duration of profound hearing
loss in the affected ear does not appear to have influenced whether the subject
decided to be implanted. It is assumed that having a longer period to adapt to
the UPSHL, the individual may have developed better coping strategies to
counteract the difficulties experienced with their hearing loss. Burkey et al.
(2006) reported that adaptation to monaural hearing was one of the reasons
their UPSHL subjects chose not undergo an evaluation for a BAHA, which did
not appear to be the case in this study.
In this current study, the number of subjects who were assessed for a BAHA,
more males chose not to be implanted, however this was not statistically
significant. The implanted and non-implanted subject groups were not matched
for education or socio-economic status. However, it was felt that the
recruitment of subjects from private otolaryngology practices would have
presented a relatively homogenous group.
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7.1.2 Hearing loss group classification
The subjects with an acquired UPSHL were divided into two groups depending
on the age of hearing loss onset. This division was based on cochlear implant
studies regarding the critical period for central binaural development. Cochlear
implant studies of unilateral and bilateral users have shown that there is a
critical period for the development of sound localisation and speech
understanding in noise (Litovsky, 2007). This critical period is reported to be
primarily in the first three and half years of life for some areas of neural plasticity
and central auditory integration. Studies measuring cortical auditory evoked
potentials (CAEPs) have shown that this critical period remains open to seven
years of age and completely closes by 12 years of age. Early implantation and
long-term unilateral cochlear implant usage has not been adequate in
preserving the plasticity of auditory pathways to the opposite ear. (Peters,
2007). Hence, the age of onset before or after 12 years of age was used to
classify the subjects.
However, there were only a few individuals who had lost hearing before the age
of 12 years. Within the implanted group only one person had acquired a
hearing loss before the age of 12, and only one subject had a congenital
hearing loss. In the non-implanted group, one subject had been classified with
a congenital hearing loss, while there were six subjects who had acquired their
hearing loss after the age of 12 years. Therefore, although there is evidence
that the critical period of binaural hearing development is up to 12 years of age,
the low numbers of subjects meant that the two groups could not be compared
and that the results from these individuals can only be used as case studies.
7.1.3 Implantation uptake of the subject group
In this study of 56 subjects, 37.5% were implanted with a BAHA for their
UPSHL. This is a similar implantation rate to that found in a study by Burkey et
al. (2006) that reported that although 94% of subjects with SSD wanted to trial
the BAHA device during a trial period on the test band. The reasons given by
subjects not to trial the BAHA on a test band included adaptation to monaural
hearing, aversion to surgery, cosmetic concerns, and belief that the device
would not alleviate the tinnitus in the affected ear. Of those subjects who
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underwent a trial with the BAHA, only 27.3% proceeded with BAHA surgery.
The main reason given for non-implantation was inadequate health insurance
cover for the device and surgery, which was not surprising as this was an
American study.
Snik et al. (2005) also reported a low uptake of BAHA implantation by subjects
with a UPSHL. After a pre-operative trial with the powerful Classic 300 model
on the steel headband, about 25% of the individuals experienced insufficient
benefit and stopped using the device during the trial period. The authors
reported that this low uptake of BAHA implantation by subjects with a UPSHL
was due to their high expectations, particularly concerning directional hearing,
with only about one third undergoing surgery after the trials. High expectations
were a reason that the majority of the subjects in this study did not proceed with
implantation as they felt the trial BAHA device did not give them adequate
benefit. One subject in particular (S11) waited for the Divino with its in-built
directional microphone to be released before proceeding with implantation
having previously had a trial with the Compact model. This subject had
discussions with an implanted subject (S8) who had upgraded from a Compact
to a Divino model to gauge this subject’s perspective on the difference in the
performance of two devices, as well as another BAHA trial - the second being
with the Divino model.
It was thus recommended that counselling prior to implantation be of the
upmost importance. Counselling is of particular importance if reduction of the
acoustic head shadow effect is a primary factor for consideration of a BAHA for
UPSHL for individuals due to their lifestyle and occupation. Wearing a BAHA
on a headband during a trial period is important for these individuals to evaluate
whether it helps their hearing in those particular situations.
The proposal for this study stated that a sample of about 30 implanted subjects
was required in order to show statistically significant changes. After exclusion
of subjects who did not fit the study criteria, pre-operative assessment subject
numbers were 56. However, the number of subjects who went on to be
implanted was substantially lower (37.5%) and comparable to the uptake
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percentages reported in previous studies. The low uptake in this study may
have been due to several factors. With 17 of those assessed (30.3%) already
having undergone major surgery for the removal of tumours (VS and cochlear
tumours), they may have been adverse to further surgery. Only six of these 17
subjects (35%) went on to have BAHA implantation.
Unlike Burkey et al. (2006) who reported that the main reason for individuals not
proceeding with a BAHA was due to the financial cost, this was unlikely to be a
major factor in this study. Subjects undergoing pre-operative assessment were
referred by private otolaryngology clinics and the majority of the subjects had
private health insurance. However, for a small percentage of subjects, financial
cost of the implant may have been a deciding factor, as the BAHA device for
UPSHL is still not provided in the public hospitals under a Medicare provision in
Australia. It is also not covered by the Office of Hearing Services, which is the
Commonwealth of Australia’s program for provision of rehabilitation devices to
aid hearing loss for eligible individuals. There may still have been out-of-pocket
expenses that were not fully covered by private health insurance, which may
have affected some of the subjects’ decision making. The cost of the surgery
and the device to individuals who did not have private health insurance may
have been up to $12,000 in Australia. For the subjects who decided to proceed
with implantation, all of them obtained their BAHA device through their private
health insurance, which covered the cost of abutment implantation and the
external sound processor.
The BAHA device requires daily cleaning, good dexterity to place the sound
processor on the abutment, and general maintenance of the device and its
associated costs for batteries and repairs. This long-term commitment may
have been an issue for some individuals in deciding not to proceed with
implantation. Hakansson, Eeg-Olofsson, Reinfeldt, Stenfelt & Granstrom (2008)
reported that subject rejection of the BAHA as a treatment device may be due to
the stigma of the abutment protruding from the head. However, this was not
reported by any of the subjects in this study as a reason for not proceeding with
BAHA implantation. Subjects were asked to fill out a questionnaire after trialling
the BAHA on a soft and hard band for two weeks. The usual feedback was that
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they did not proceed with implantation as they did not gain sufficient benefit
from the trial device. The trial device may have been a Compact or a Classic
300 depending on device availability, which may have influenced the subject as
to whether to proceed with implantation. The Compact model is the weaker of
the two, and it is possible that the subject may have obtained little benefit from it
due to the trial relying on transmission of sound through skin, soft tissue and
hair.
It was initially reported from the panel group in Snik et al.’s (2005) paper that
during the trial period of BAHA devices for UPSHL, some subjects preferred the
more powerful Classic 300 to the Compact model. Since then, the
manufacturer (Cochlear Limited, Australia) has reported that there are some
individuals who require additional amplification force to overcome increased
interaural attenuation to provide sufficient loudness in the non-affected ear.
They recommended that the Intenso model be fitted to these individuals (Flynn,
2008). This issue was also raised within this study’s audiology clinics via
anecdotal reports by subjects who when given either a Classic 300 or Intenso
as a loan device when their own device was being repaired, preferred the loan
device to their fitted Compact. Two long-term subjects from this study have
since up-graded to the Intenso device in 2008. This study did not include data
from these subjects after their up-grade.
7.1 4 Implanted subject numbers
There were 21 subjects implanted with the BAHA device. The subjects were
assessed with tests at set intervals, so there were staggered results, depending
on when the person was implanted, with some subjects having been assessed
over a two-year period, whilst others were tested over a 12-month period post-
implantation. There were also delays in the uptake of implantation after the pre-
operative assessment as a number of subjects waited for the Divino model to
be released with TGA approval and the associated private health insurance
rebates. This delay resulted in the external sound processor being fitted to
these individuals up to six months later than initially anticipated.
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There was also a delay in the uptake of a BAHA by one subject who trialled a
WiFi CROS amplification system. A CROS system was offered to all subjects
following their BAHA assessment. The newer CROS device, the WiFi system
with a FM signal linking the two units was released by Unitron (Phonak Hearing
Solutions) in 2005 with potentially better outcomes possible than those
achieved with a hard-wired CROS system. The trial of the WiFi CROS device
took two months, but the subject did not find it beneficial, experiencing the
“occlusion effect” in the non-affected ear. Therefore, the subject decided to
proceed with BAHA implantation after first trialling the BAHA on the headband.
It was vital that osseointegration had occurred before the external sound
processor was loaded on to the abutment. The time for osseointegration was
two months for all of the implanted subjects, except for one subject (S12) whose
sound processor was fitted three months post-surgery. In addition, the interval
between the post-operative results varied as post-operative assessments were
at times difficult to schedule with the audiologists’ clinical caseloads if there was
non-compliance with subject’s attendance to the set appointments. The delays
resulted in reduced numbers of subjects recruited who had undergone the full
two years of post-operative assessments.
7.2 Speech testing
The findings on speech perception in quiet and noise reported in this study
should be viewed as a pilot study to look at the development of protocols for
assessing these subjects. In this study the aim was to determine whether there
was any significant difference in the subjects’ pre- and post-operative
assessment of speech perception results when using a BAHA device on a test
band versus the BAHA on the subject’s abutment or unaided.
The speech perception testing provided limited data. Subjects were tested with
one of three speech perception testing protocols depending on the time they
had their pre-operative assessment. Despite combining Group B and Group
C’s results, small subject numbers in each of the comparative groups made it
difficult to make any statistical comparisons between pre- and post-operative
speech test results. Sargent et al. (2001) found that subjects with a unilateral
severe to profound SNHL had marked variability in individual performances
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when tested with single words and sentences under different noise conditions;
which was also reflected in this study’s results.
The objective of the pre-operative speech perception assessment was to
determine whether there was a significant difference in the subject’s aided
performance (with a BAHA test device on a test band) versus their unaided
performance. Having a test band meant there was a microphone present on
the affected side to amplify speech to the non-affected ear. How effective this
microphone was reflected how well the sound was transmitted to the non-
affected ear, particularly in the presence of background noise.
7.2.1 Speech testing in quiet
In examining the pre- and post-operative abilities of the subjects, the aim was to
determine whether having a microphone to pick up sound via the BAHA
reduced the overall presentation level required for the subjects to discriminate
the test material (AB words) when compared to the unaided condition.
The test material chosen to assess speech understanding in quiet, both fixed
and adaptive procedures was AB words. Initially, fixed levels were used with a
predetermined presentation level to obtain percentage correct scores to
compare aided and unaided results. Speech testing reliability, sensitivity and
validity were to be used with Thornton and Raffin (1978) model to determine
variability across repetitions of speech discrimination tests with a 95%
confidence level.
As more subjects were assessed, it was noted that ceiling effects were
occurring due to the fixed presentation levels in pre- and post-operative cases.
Thiboudau (2000) reported that an advantage of adaptive test procedures over
fixed presentation levels is reduced ceiling and floor effects. The other issue
when conducting speech testing amongst subjects with hearing impairment is
that the results generally show a wide range of standard deviation when speech
tests are conducted with percentages correct with set levels (Welsh et al.,
2004). Due to these two reasons, an adaptive SNR level test procedure was
included in the test protocols. This adaptive procedure determined the intensity
125
level necessary to achieve a 50% speech recognition threshold (SRT). The
adaptive procedure was used initially used with 2dB steps, but then was
reduced to 1dB steps when testing in quiet and noise.
It was predicted that there may be a small advantage when using the BAHA in
quiet conditions. Studies of bilateral hearing show up to 3dB advantage due to
the binaural summation rule, however these figures were based on two working
cochleae working in unison. Binaural summation is a quantifiable improvement
in the thresholds for speech stimuli when the signal is presented to both ears
simultaneously at levels appropriate for the hearing loss (Sargent et al., 2001).
The subjects in this study had only one working cochlea, with the sound
transferred to this functional cochlea via bone conduction. Snik et al. (1998b)
found that when testing SRT in quiet, their results showed 3 to 6 dB
improvement with binaural BAHA fittings. They concluded that improvement of
SRT in quiet is due to the dichotic summation of sound with the two ears at a
central auditory level. However, Snik et al.(1998b)’s study was conducted using
subjects with two working cochleae as their BAHA subjects had conductive
hearing losses.
In this study Group A’s speech perception results in quiet did show a significant
correlation between testing with a BAHA on a test band and the results
following BAHA implantation. The results showed a treatment effect, which was
greater than expected, as although hearing in quiet may be an issue for some
individuals with a UPSHL, it is not usually the primary area of concern (Sargent
et al., 2001).
No substantial evidence of a BAHA advantage was obtained from the Group
B/C’s speech in quiet pre- and post-operative testing results. In the pre-
operative condition, the majority of the subjects in Group B/C showed no
difference between their speech discrimination ability with the BAHA on a test
band compared to the unaided condition as they scored between 40% to 60%
correct in both conditions at the same presentation level. This indicated that
wearing the BAHA device during the testing did not disadvantage the subjects.
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Pre-operatively, there were four subjects who did have a difference in the
presentation level to obtain the SRT with the BAHA on the test band compared
to the unaided condition. Of these four subjects, three obtained the predicted
result with a lower presentation level required to achieve SRT when wearing the
BAHA on the test band. The other subject’s performance was worse with the
BAHA on the test band than when unaided, as this subject required a higher
presentation level when wearing the test band. This subject may have found
the increased level of the speech distracting, however no notes were made to
indicate the subjects reaction to the sound quality perceived when wearing the
device as this was not a requirement by the audiologist in the study. Whether
this pre-operative testing result may have influenced that the subject’s choice
not to proceed to implantation is unknown, as two of the other subjects who did
have a significant benefit with the BAHA in quiet also chose not to be implanted.
Supporting the statistically significant results of Group A’s speech in quiet
results were the subjective responses of the implanted subjects in the outcome
measures which also reflected a positive improvement in hearing in quiet
situations. The APHAB subscale EC relates to hearing in quiet situations. The
implanted subjects’ results showed a significant improvement in this subscale
between the pre-operative and the short-term post-operative responses. There
was significant correlation with pre-operative and short-term post-operative
responses, indicating initial improvement, but the effect was not significant long-
term.
Similarly, the first two pre-determined questions of the GHABP address hearing
in quiet. The subjects are asked to rate their ability to hear the television at the
same volume level as family and friends, as well as their ability to have a
conversation with one person when there is no background noise. There was a
significant improvement in the implanted subjects’ ability post-operatively in
regards the disability subscale, reflecting the subjects’ perception of their ability
to hear in quiet.
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The post-operative responses to questions in the SSDQ relating to hearing in
quiet also indicated an improvement in hearing in quiet by the implanted
subjects. For example, in response to the following question from the SSDQ,
“How do you assess the value of your new device in the following situation
compared to your previous situation (unaided) - talking to one person in a quiet
situation?”, 88% of the implanted subjects reported they heard better in that
situation with their BAHA device. Seventy-seven percent of subjects continued
to respond positively to this question when completing the long-term SSDQ.
The findings of an improvement in the performance by the implanted subjects in
both speech testing as well as positive responses in the questionnaires
suggests that hearing in quiet was a genuine issue for the UPSHL subjects.
Having to rely one ear when hearing soft speech may be tiring for these
subjects, hence receiving a louder signal from the BAHA in combination with
their hearing in the non-affected ear may have assisted the implanted subjects
in their perception of speech. Also the SSDQ includes the response option of
“no difference” to the question relating to the hearing in quiet, therefore the
implanted subjects’ response that the device did make a difference was not
simply answering the question as yes or no.
7.3 Speech-in-noise testing
As the subject group had a UPSHL that did not have specifically designed,
standardised audiological testing procedures, the test design was based on
literature searches.
As the study progressed, several changes were made to the speech testing
protocol. This was necessary because of ceiling effects with the speech testing
in quiet and in noise due to fixed presentation levels. Initially, the speech was
presented in a free-field at 65dB SPL and the competing speech noise (four-
speaker babble) was presented at fixed signal-to-noise ratios (SNR) of 10 dB, -
10 dB and 0 dB. Thus the noise was either 10dB greater than the target speech
stimulus, 10 dB less than the target stimulus or at the same level as the target
stimulus. These levels were chosen as published studies had shown that these
SNRs, particularly the SNR of +10 dB represented normal social speech noise
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levels (Welsh et al., 2004). In some cases, the ceiling effect was occurred in
the pre-operative testing, therefore the fixed SNR levels for testing in noise
were further refined to +5, 0 and –5. However it was found that the ceiling and
floor effects were occurring with post-surgery testing once subjects were aided
with the BAHA in-situ rather than the BAHA on a test band. Therefore, the
protocols for testing speech-in-noise were once again modified.
The final modification to speech-in-noise assessment protocols involved using
an adaptive procedure to determine the intensity level necessary to achieve
50% speech understanding. The final adaptive procedure used 1dB steps in
adjusting the noise level. A previously formulated protocol used for testing
speech-in-noise in a hearing aid study (Davis et al., 2001) was adapted to
develop a specific speech-in-noise flow-chart for the audiologists to follow when
testing in noise. However, when testing subjects it was found that there were
two problems with the initial flow-chart when performing speech testing in noise.
Firstly, there were not enough speech lists to establish between 40% and 60%
correct in both the aided and unaided conditions with the number of different
noise array conditions. Secondly, it was difficult to obtain a SNR difference with
the large range of accepted percentages between aided and unaided
conditions. The subject would perform better aided with the BAHA on a test rod
rather than unaided, but it was within the allowed 20% variance, so no
significant change in SNR was detected.
Therefore, the test protocol was changed to a protocol described by Davis et al.
(2001) in which a SNR threshold was obtained using an adaptive procedure
with guidelines to setting the initial SNR levels. A flow-chart was created to
guide the audiologists through the test protocols with speech testing in noise.
After initial testing, it was discovered that this protocol was not discrete enough
with SNR levels being 2dB, and the percentage correct being too wide a
variation at 20% (i.e. 40-60% correct). The protocol was adapted in an attempt
to achieve a SRT percentage closer to 50%.
Therefore, the speech testing in noise flow-chart was revised (see Appendix III).
The accepted percentage range correct was narrowed closer to the speech
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recognition threshold (SRT) of 50% (48% to 52%) with 1dB step changes in the
noise presentation levels, instead of the step size of 2dB which decreased the
subjects score fluctuation. This up-and-down adaptive procedure with a fixed
step size of 1dB was used to determine the SRT in noise. Two lists were
presented at the SRT level, and an average was calculated to determine the
SNR in dB.
Researchers have used different terms to report findings of speech-in-noise
testing. Plomp (1986) used the term “hearing loss for speech-in-noise” to
indicate the increase in SNR in dB needed for a recognition score of 50%
correct compared to normal performance. Killion (1997a) described this level
as “SNR loss”. In this study, this SNR in dB was called the Optimal Signal-to-
noise ratio (Davis et al., 2001).
It was decided not to block the non-affected ear with a noise occluding earplug
which was part of previously reported study by Wazen et al. (2003) when they
examined the subjects’ performance with the devices in speech testing. The
reasoning for this was, to evaluate the overall performance of the subjects as
they would perform in a noisy environment in their daily activities.
The aims of testing speech-in-noise were to identify subject factors, which could
predict the suitability and potential outcomes of individuals implanted with a
BAHA. It was predicted that there would be an improvement in speech
understanding in noise with the BAHA on a test band compared to the unaided
condition, with further improvement after the subject was implanted. It was not
possible to achieve these aims as several modifications to the test protocol
throughout the study resulted in the number of comparable results being too
small for statistical significance.
The results of the study showed that when assessing subjects using the first
protocol with testing at fixed SNR levels, it was prone to ceiling and floor effects.
With extremely high or low percentage scores pre-operatively, it was difficult to
prove a treatment effect from the BAHA post-operatively. This was reflected in
the results from the Group A speech-in-noise testing showing no significant
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correlation between pre-operative testing of the BAHA on the test band to post-
operative testing with the BAHA or unaided.
The protocols described in the speech flow-chart were also compromised by the
number of BKB/A sentence lists required to obtain the SRT with the adaptive
SNR protocols. This may have been due to the speech stimulus, as despite the
change in step size of the SNR to 1dB, it was difficult to achieve speech-in-
noise scores close to 50% when testing in the study. The sentence length may
have been a factor as well as the amount of sentence lists administered at each
level. Thus the test protocols were not sensitive enough to detect a 1dB
change in SNR when using BKB/A sentences as the test material.
Furthermore, there was even difficulty achieving scores 40% and 60% with the
Group B test protocol, revealing inconsistent subject performance. This may
have resulted from the effect of noise on the subject. Welsh et al. (2004)
suggested that auditory overload or cognitive distractions may result in
inconsistent performance in speech-in-noise testing. This may have been the
case in this study as the subjects had to undergo strenuous testing with
numerous sentence lists with increasing and decreasing noise levels. Most
subjects required at least fourteen lists of sentences to obtain their SRT for the
three noise conditions.
Researchers, Keider et al. (2002) reported that four of the sentence lists in the
BKB/A test had greater variability in difficulty compared to the other sentence
lists, so they were excluded from this study’s test protocol. This significantly
reduced the overall number of lists available, and in the majority of cases when
performing the pre-operative assessment nearly all of the 17 available sentence
lists were used. This meant that all subjects had prior exposure to the majority
of the sentence list material at their post-operative assessment.
There was a period of up to six months between pre-and post-operative testing
for surgery and osseointegration to occur, and therefore the practice effect may
have not occurred at this stage. However, repetitive testing of the same test
material at set intervals at the post-operative appointments may have been
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affected by the practice effect, with subjects remembering the content of the
sentences. This may have influenced the results, particularly with the implanted
subjects who were tested for two years, hence resulting in the improvement in
SNR over time as demonstrated in the results of subject fourteen (S14).
Due to the small number of implanted subjects who were tested using the
adaptive speech-in-noise testing procedure, the post-operative findings are
inconclusive. However, the results of the implanted subjects showed that the
range of SNR was from -8dB to +5dB to achieve SRT with either the BAHA on a
test band or with the BAHA once implanted, as well as a trend towards a
reduction in the SNR with implantation over time according to the direction from
which the noise originated.
Results from studies of subjects with normal hearing, bilateral hearing loss or
cochlear implants can only act as a guide to compare the SNR of subjects with
a UPSHL as it is difficult to directly relate SNR figures to this group as they have
normal hearing in one ear. Individuals with a hearing loss require better signal-
to-noise ratios than those with normal hearing thresholds. Killion (1997a)
reported that to discriminate speech, the greater the individual’s hearing loss,
the greater the SNR is required. On average, individuals with severe to
profound hearing loss needed an estimated SNR 12-18 dB to achieve a 50%
correct score when tested with sentences at 70dB HL (83dB SPL) as shown in
Figure 7.1.
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0 5 10 15 20
20
30
40
50
60
70
*80
*90
Hea
ring
loss
in d
B (3
FPTA
Signal to noise ratio in dB
SNR required for 50% correct in sentence test
Figure 7.1. Adaptation of Killion (1997b)’s data of the relationship between hearing loss and SNR.
NB: * indicates an estimated SNR for hearing loss levels.
Note. From (Killion, 1997b)
Versfeld, Daalder, Festen & Houtgast (2000) reported that the SNR required to
obtain 50% correct for sentences in subjects with hearing within normal limits
was –4dB. Cochlear implant users have been reported to require a SNR
between +5 and +15dB, which is on average a SNR at least 10dB to 25dB
higher than for normal hearing subjects (Spriet et al., 2007).
Sargent et al. (2001) in their study comparing the abilities of normal hearing
individuals and those with a unilateral severe to profound SNHL with single
word and sentence tests in quiet and noise. They found that when examining
speech-in-noise testing, the condition in which the poorest result in performance
was when the noise was directed towards the better ear of the unilaterally
hearing impaired subjects. Whilst Sargent et al. (2001) published results of
percentages correct obtained when testing speech in quiet and in noise using
fixed SNR and presentation levels, reports of studies to examine the SNR
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required to obtain a SRT for sentences for subjects with a UPSHL have been
limited to those studies examining the BAHA fittings with UPSHL subjects.
Lin et al. (2006) examined eighteen subjects with the sentence test, Hearing In
Noise Test (HINT), with a constant background noise level of 65 dB (A). Their
finding showed a BAHA advantage when the noise was presented to the non-
affected ear compared to the subject’s unaided performance. They also found
this advantage when they tested the same subjects with a CROS hearing aid.
A smaller number of their subjects had a BAHA or CROS hearing aid advantage
when the noise was presented to their worse ear. However, these results were
for both BAHA users with UPSHL, as well as five subjects with a profound
hearing loss in one ear and a moderate SNHL in the other ear, and the average
SNR for the subjects was not given for any of the speech-in-noise test
conditions.
Examining the data presented in their paper indicates a range of SNR from
approximately +3 dB to –8 dB for a SRT when noise was presented to the non-
affected ear, while the range of SNR appeared to be 6 dB to –2 dB for a SRT
when the noise was presented to the deaf ear. These researchers found no
difference between the aided and unaided condition when the speech and noise
was presented in front of the subject.
Bosman et al. (2003) reported with seven BAHA subjects with UPSHL had a
SNR of -3.5 dB for a SRT when speech was presented to the non-affected ear,
and a SNR of -0.5 dB for a SRT when the speech was presented to the affected
ear for the BAHA. The noise in this study was presented from a speaker in front
of the subject.
In one of the key studies comparing use of a traditional CROS aid, the BAHA
and the unaided condition in ten subjects with UPSHL, Niparko et al. (2003)
reported their speech-in-noise testing using the HINT. They described the HINT
threshold as the decibel SNR where the subject scores 50% correct or obtains a
SRT. They reported that for every 1 dB change in the SNR when obtaining
SRT, this equalled a 10% change in speech intelligibility. When testing their
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subjects with noise and speech being presented in front, they reported a 1.2 dB
BAHA advantage when testing with the HINT. This result was significant
(p<0.05) when a comparison between unaided and aiding with the BAHA was
conducted.
Niparko et al. (2003) reported a significant BAHA advantage being 4.4 dB SNR
when noise was presented to the better ear. They reported an unaided
advantage of 2.4 dB SNR when the noise was presented to the worse ear. The
authors reported on a composite speech-in-noise testing score, which was the
average SNR of the three test conditions. They reported a significant BAHA
advantage of 1.1 dB SNR across the three noise conditions. As the speech
material they used was different to the one used in this study and the limited
data obtained from this study in speech-in-noise testing, no direct comparison
could be made. However, Niparko et al.’s general findings were that the BAHA
showed a larger advantage compared to the CROS and unaided conditions;
and that the BAHA had the greatest advantage in lowering the SNR when the
noise was presented to the non-affected ear.
Newman et al. (2008) using similar speech-in-noise testing protocols to Niparko
et al. (2003), to assess subjects with BAHA for UPSHL showed an improvement
in speech understanding in noise following BAHA implantation with lower SNRs
representing better performance, but a wide variation across subjects’ results
and the intervals at which they were assessed post-operatively.. Their results
were reported as a mean of all the SNRs from four directions of noise
conditions. They used the HINT as the speech material and fixed their noise
level, altering the speech stimuli presentation level, whereas it was the opposite
in this current study.
It was predicted that when assessing speech perception in noise with the
provision of a BAHA would result in an improvement of the signal-to-noise ratio
level. This advantage was predicted to be at least 1dB in the pre-operative
condition of BAHA on test band, as well as post-operatively when compared to
the unaided condition for each subject.
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7.3.1 Testing in S0:N0 condition
The test condition with the speech and noise being presented from the same
speaker in front of the subject reflects binaural redundancy. Binaural hearing
gives the listener 1 to 2 dB SNR advantage compared to the monaural condition
(Peters, 2007). Speech in front of the subject is considered to be the most
natural listening situation for noisy environments as the listener will most likely
face the target speaker (Snik, et al., 1998a). When speech and noise is
presented in front of a subject from the same distance, the signal to noise is
similar in both ears. When the fixed SNR levels were examined for Group A,
the results showed no significant difference between unaided and test band
results, the test band and BAHA results, or the unaided to BAHA results.
The speech-in-noise test protocols used for Groups B and C used an adaptive
SNR paradigm. In this study, the average test band advantage at the pre-
operative testing was 0.08 SNR, which indicates no binaural summation or
redundancy effects with the BAHA on the test band. This result was poorer
than the 1.2dB BAHA advantage that Niparko et al. (2003) described in their
study with BAHA for UPSHL. However, Lin et al. (2006) who conducted
speech-in-noise testing using the same speech material and protocol of a fixed
noise level and adaptive levels of the speech stimuli as Niparko et al. (2003),
found no difference between the aided and unaided condition when the speech
and noise was presented in front of the subject.
There were only four subjects (S13, S14, S16 and S17) tested in this protocol
post-operatively. There was one subject (S14) who showed a decrease in
performance following the BAHA fitting when tested in the S0:N0 condition.
However, subject thirteen showed no change in the SNR required to obtain SRT
between pre- and post-operative testing. Overall the results in this study
showed no advantage to being aided with a BAHA either on a test band pre-
operatively or with the fitted BAHA post-operatively. Snik et al. (2004) reported
that a BAHA fitted as a transcranial BAHA CROS is not expected to have any
significant effect on binaural summation, which are confirmed in Lin et al.’s
(2006) study and by the limited data in this study.
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7.3.2 Testing in S0:N90/S0:N270 conditions
Spatial separation of targeted speech from competing noise makes it easier to
hear the speech (1997). When the noise and speech is separated, binaural
squelch is utilised as the listener receives the signal at different SNRs at each
ear.
It was anticipated that the greatest advantage with the BAHA on the test band
and post-operatively would occur when the noise signal was presented to the
non-affected ear. The separation of the noise and speech would give the
subject an advantage, as having the microphone of the BAHA will assist in
overcoming the head shadow effect when the noise was presented to the
opposite side. It would result in the speech signal being picked up on the
microphone of the BAHA and transferred across the skull to the working
cochlea. In this study, it was predicted that there would be improvement of 1dB
SNR in the S0:S270 condition as all the subjects’ results were corrected for a
right UPSHL.
When the noise was presented to the side with the BAHA microphone the
opposite would occur. This would result in the working cochlea receiving a
noise signal whereas it normally would not in the unaided condition. Having a
second signal potentially causes an issue of cross masking when the noise
signal from the BAHA would interfere with the clear speech signal the working
cochlea would normally receive. In this situation, when the noise was
presented to the BAHA microphone, as in condition S0:N90, the subject would
be at a disadvantage and poorer results were the predicted outcome.
Pre-operative testing with Group A protocol, showed no significant advantage
with the test band compared to the unaided condition with a paired sample t-test
in both the S0:N90 and S0:N270 conditions. Pre-operative testing using the
speech-in-noise protocols with Groups B and C in the S0:N270 condition
showed the mean of eleven subjects’ SNR was a 0.2 dB SNR better with the
test band than unaided (for example, a test band advantage was found). While
in the assessment of the S0:N90 condition, the mean of the 18 subjects’ results
was a 0.36 dB SNR test band advantage. As the results had been corrected for
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a right-sided hearing loss, these pre-operative results showed a greater
advantage was recorded when noise was presented to the better ear, which is
not the advantage that was expected. This unexpected result may have been
due to subject fatigue as the testing procedure was conducted in a two-hour
appointment. The speech-in-noise testing required numerous BKB/A sentence
lists to determine the SRT in each condition. The protocols did not instruct the
order in which the noise signal was directed to each ear, nor was the
administration randomised between subjects or direction, hence the subjects
may have undergone testing with noise directed to their better ear in the final
stages of the testing.
Post-operatively ten subjects were assessed in Group A with a paired sample t-
test being used to compare pre-operative test band results with post-operative
BAHA scores in noise. The analysis showed that there was no significant
difference between the BAHA and the unaided condition in both S0:N90 and
S0:N270. Further analysis using the paired sample t-test showed no significant
difference between the pre-operative test band results and the BAHA results
post-operatively in these two conditions.
Four implanted subjects in Group B/C were tested in the three noise conditions.
Results showed that over time, one subject (S14)’s was able to achieve a lower
SNR level indicating improvement once fitted with the BAHA. For example, she
needed a +5 dB SNR in the S0:N270 condition at her pre-operative testing, but
–3.5 dB SNR, 2 years post-fitting with her BAHA device, showing a 8.5 dB SNR
improvement (noise was presented to her non-affected ear). Therefore, this
was the expected post-operative improvement with a BAHA as it showed a
release from the head shadow effect, and this SNR level of –3.5 dB was the
same level reported by Bosman et al. (2003) in their study of seven BAHA
subjects with UPSHL when speech was presented to the non-affected ear.
However, the other three implanted subjects tested in this protocol within this
current study did not show this. Post-operative results were limited to only four
subjects thus although some trends were apparent, the ability to draw
conclusions was limited and statistical analysis was not possible.
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In summary, the results showed no significant difference between testing with
the test band to results obtained from the BAHA with the noise source from
different directions when tested with a fixed SNR. However, it is not possible to
draw any clear conclusions from the post-operative testing results of all three
noise conditions due to limited data from implanted subjects.
7.4 Abutment and device issues
7.4.1 Post-operative skin infections and complications
The subjects’ medical and audiological records were examined to note any
observations of skin reactions. In previous studies, researchers have used the
classification system that was described by Holgers, Tjellstrom, Bjursten &
Erlandsson (1987) to classify skin reactions following the use of titanium
abutments. Stalfors & Tjellstrom (2008) used an operating microscope to
examine and rate the post-operative skin reactions according to Holgers et al.
(1987) classification system. However, in this study, the Holgers et al. (1987)
classification system was not used. Instead, the otolaryngologist and
audiologist noted skin reactions visually. Skin swabs were taken when skin
infections were persistent. Eight subjects reported skin irritations. The
dermatome was introduced during the course of the study replacing a U-shaped
incision. However, there was no apparent change in the nature or prevalence of
skin reactions that could be attributed to the use of the dermatome.
There were eight (38%) ears with single or multiple occurrences of skin
reactions in this study, which is at the higher end of the range of reported
incidences in the literature. The percentage of skin reactions is reported to
range between 3.5% to 39.6% (Lekakis et al., 2005). The wide variation would
indicate that the extent of skin reactions are reported differently and possibly
underestimated in some studies. It should be noted that previously published
studies tended to be European or United States based, so it is possible that the
hotter and drier Australian climate, with many subjects swimming and greater
levels of perspiration, may have lead to the increased number of skin reactions
in comparison to previous studies. Another possible cause for the high
incidence of skin reactions in this study could be the use of Kenacomb ointment
in this cohort. Prolonged usage can cause skin to break down. Thus, if
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subjects were not monitoring their use of the ointment or using it excessively,
skin reactions may have occurred. There has been no specific study reporting
the use of Kenacomb with BAHA.
The treatment of skin reactions is by local application of antibiotics and/or
steroid ointment (Snik et al., 2005). In some cases in this study, subjects were
prescribed topical antibiotics and oral antibiotics. Steroid ointment is prescribed
in most cases for skin reactions that occur post-operatively. It was reported by
Snik et al. (2005) that BAHA implant centres experienced a high rate of soft
tissue infections early in their surgical experience. There was a high rate of
infections in this study, which did not appear to decrease over time.
In this study, there were no cases of failed osseointegration, external impact by
trauma, osteonecrosis or fixture extrusion. These are generally issues seen in
the paediatric population, particularly the trauma to the abutment due higher
amount of physical play with children and sports. Therefore, as this study’s
subjects were an adult population, it was expected that there would be none, or
minimal occurrence of these particular BAHA post-operative complications.
7.4.2 Repair issues
Until the release of the Divino model in 2005, the external sound processor
fitted in this study was the Compact model. The sound processor model did not
make a difference in amount of repairs. There was an average of
approximately two repairs per subject. There was also one case of a faulty
Divino device being issued that was replaced by the manufacturer under
warranty. The most common BAHA faults reported by the manufacturer upon
return after repair related to dirt and moisture. When Entific Medical Systems
initially distributed the sound processors to the clinics, they were issued without
any drying device to remove moisture similar to that used for hearing aids,
particularly due to perspiration from the head and hair.
When moisture enters the internal working components of hearing aids, faults
related to corrosion are common. It was not until the acquisition of BAHA by
Cochlear Limited, in conjunction with requests by audiologists, that a drying
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device was included in the fitting package for the sound processor. The Dry &
Store conditioning system (Ear Technology Corporation, Johnson City,
Tennessee) which Cochlear Limited also distributes with its cochlear implants,
is now included routinely in all BAHA fitting packs, which resulted in reduced
amount of repairs due to moisture. This device is shown in Figure 7.2.
Figure 7.2. Dry & Store cleaning and drying device.
Note. From (Ear Technology Corporation, 2008).
Four of the subjects had the transducer within the BAHA device replaced due to
issues with the air gap collapsing. Without this space, the transducer will not
work effectively and transfer the vibratory motion across to the implant. This in
turn affects the sound quality of the device, with subjects reporting weak sound
output, distortion or a non-functioning device.
Subject (S15) who was diagnosed with a congenital UPSHL continues to wear
her BAHA, four years post-fitting despite recording the greatest number of
repairs to her speech processor. This finding indicates the reliance that she has
on wearing her BAHA and benefit received from this device.
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7.4.3 Abutment removal and discontinued usage of BAHA
In this study, three subjects required surgical removal of their abutment. One
subject (S18) had her abutment repositioned. Subject (S1) had his abutment
removed as he felt the device did not provide his expected benefit. He was
offered a trial of the Divino sound processor as he had been fitted with the
Compact model, but he was not interested. His abutment was removed two
years and four months post-fitting of the sound processor.
This subject was one of the first implanted in the study; therefore he may have
high expectations from the new application of a rehabilitation device for UPSHL.
His specific hearing difficulties as indicated on the GHABP included “hearing
conversation in the presence of machinery noise” as well as “hearing at a busy
restaurant”. This subject’s GHABP initial disability and handicap scale scores
were 71.8 and 78, respectively. These scale scores were amongst the highest
of the implanted subjects pre-operatively, as this group’s averages for the two
scales scores were 55 for the initial disability and 62.1 for the handicap scale
scores.
This subject’s post-operative residual disability scale score reduced to 50,
indicating there was improvement in hearing from the fitting of a BAHA.
However, he rated his post-operative satisfaction and benefit as the lowest
possible on the scale scores. This subject’s reported use of the device was one
of the lowest reported for the implanted subjects in the GHABP as well.
However, this is understandable if limited benefit and satisfaction from wearing
the device was reported. The evolution of the counselling of potential subjects
with UPSHL regarding BAHA has improved with the manufacturer, Cochlear
Limited providing increased clinical literature on how to effectively counsel
individuals with UPSHL about what to expect with the BAHA when hearing in
noisy situations. Therefore, perhaps this subject’s expectations would have
become more realistic regarding noise and better listening strategies may have
been provided regarding positioning the BAHA in relation to the direction of the
noise source if this information had been available prior to his surgery.
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The second subject (S12) had her abutment removed due to unexplained
chronic pain from the implant site that was consistently reported post-
operatively, with or without the device attached. Although the subject tried to
persevere with the BAHA as she found it of some benefit, the pain affected her
quality of life. She had her abutment removed one year and two months from
the date the sound processor was fitted. Snik et al. (2005) reported that chronic
pain at the implant site occasionally becomes resistant to conservative
treatment and requires surgical retrieval of the implant. This occurs in less than
1% of individuals fitted with a BAHA. Mylanus et al. (1998) reported a higher
incidence with two subjects in a study of thirty-four subjects (5.8%)
discontinuing use of their BAHA due to experiencing unexplained pain when
using the device.
A further two subjects (S7 and S10) discontinued use of their BAHA with the
Compact sound processor as they reported limited benefit. Both had trialled the
Divino model to compare its performance, but felt there was some, but little
difference in performance. The upgrading cost was an issue for both subjects
as their private health funds would not upgrade the device without having the
full BAHA surgery again, or waiting several years until deemed eligible for an
upgrade under the provisions of the health fund. The two subjects had
continued to wear their devices intermittently despite reporting lack of benefit,
requiring repairs and/or issues with the skin around their abutment. They
stopped wearing their devices completely at 2 year 6 months (S7) and three
years and five months (S10) post-fitting.
Subject (S10) continued to experience a “weeping discharge” from her
abutment, but did not follow this up despite advice to see her BAHA surgeon, as
she reported that she was happy managing it through her general practitioner.
She was the only subject in the study who had a 3mm fixture; all other subjects
had the 4mm fixture. The 3mm fixture was used as she was one of the first
subjects to undergo the operation in that particular BAHA clinic, as well as her
previous VS surgery. Neither subject had trialled the stronger Intenso device
when they withdrew from the study. Therefore, this may be a future
consideration as both subjects have retained their abutments.
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7.5 Questionnaires
Several questionnaires were used in this study to assess the positive and
negative aspects of BAHA use in real life situations which could not be
evaluated by conventional audiological evaluation. The aim of administrating
pre- and post-operative outcome measures was to determine subjective
improvement following the fitting of the BAHA. Three months is required for
individuals to become accustomed to the BAHA device and for final adjustments
(Shanker et al., 2004), and so the first questionnaire was not administered until
this time had elapsed. Direct studies looking at fittings of BAHA for UPSHL
have found that self-report questionnaires mailed to subjects one year post-
operatively showed positive results with a limited number of individuals who
were no longer using their BAHA device (Snik et al., 2005).
7.5.1 APHAB
This study has shown significant differences between the pre-operative and
post-operative scores across all four subscales of the APHAB. There was a
continued significant improvement between the pre-operative and long-term
post-operative APHAB scores overall, as well as in the BN and RV subscales.
Furthermore, the short and long-term post-operative results was examined.
There was a significant improvement in the overall average of the APHAB
subscale, as well as in the EC and BN subscales. These results showed that
the BAHA provided improvement in subjects’ reported quality of life after being
fitted with a BAHA for UPSHL. Although there was reduction in the perceived
benefit over time, the implanted subjects still reported that they obtained benefit
from the BAHA device.
Examining some of the individual implanted subjects’ APHAB overall means
across the four subscales and their perceived benefit from the outcome
responses, subjects: S6, S8, S16, S17 and S20, obtained the greatest reported
benefit from the BAHA. Furthermore, two of the four subjects who stopped
wearing their BAHA were in the middle of the distribution of the range of APHAB
scores and had reported no real change long-term when re-examined. Another
subject who stopped wearing the BAHA (S10) had extremely low APHAB
144
subscale scores short-term and long-term post-operatively, compared to the
other implanted subjects. These low APHAB subscale scores indicate that she
did perceive benefit from the device. This discrepancy of reporting benefit in
her outcome measures but discontinuing the use of the BAHA device may be
due to the questionnaires being affected by positive bias as the subject feels
grateful for intervention. The questionnaires responses were discussed with the
audiologist at the appointments and there may have been a need for the subject
to please the examiner.
Another area that can be examined with regards to the APHAB is the pre-
operative scores in each of the subscales to see if there is any indication of
which subjects would benefit more or less from BAHA implantation. Upon
examination it was found that subjects who had a high score, i.e. reported
greater difficulties pre-operatively, did not necessarily gain greater benefit from
the device post-operatively.
Additionally some of subjects who reported a great amount of hearing difficulty
pre-operatively did not proceed with BAHA implantation. The highest pre-
operative APHAB score was from the non-implanted subject (S55). Conversely,
the subject (S11) who had the lowest score on the pre-operative APHAB did
proceed with implantation. However, it should be noted that this subject was
the only subject who trialled a WiFi CROS system during the study and also
waited until the release of the Divino model before proceeding with implantation.
He indicated that he was unsure whether to proceed with implantation before
trialling a WiFi system and sought recommendations from other BAHA
implantees regarding different sound processor models before proceeding with
the surgery. Therefore, the degree of difficulty at initial assessment reported
with the APHAB does not appear to be a predictor of whether the subject went
onto to have surgery.
In this study, both of the implanted and non-implanted subject groups reported
on their pre-operative APHAB questionnaire that the ability to hear in the
presence of background noise was the biggest issue, with the BN subscale
score being the highest of all subscales for 86.5% of the subjects. The
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implanted subjects’ results showed a significant improvement in their post-
operative scores in the BN subscale. The significant change in pre-operative
and post-operative BN subscale scores indicated that the BAHA is an effective
treatment for this particular set of hearing difficulties.
7.5.2 GHABP
The aim of administrating the GHABP questionnaire to the subjects was to
examine the extent to which the BAHA was effective in reducing subjects’
reported disability and handicap, as well as their short and long-term benefit,
use and satisfaction with the device. The major reason for the inclusion of this
questionnaire to supplement the outcome measures of the APHAB and SSDQ
was that subjects were able to nominate their individual hearing difficulties,
unlike the other questionnaires with their predetermined set of questions.
In analysing the post-operative results, the scores were a reflection of the
treatment effect of the BAHA to hearing difficulties particular to UPSHL.
Seventeen implanted subjects’ results were used to compare the pre-operative
responses to the short-term post-operative responses. Two subjects’ pre-
operative GHABP results were missing, while another two implanted post-
operative GHABP results were not conducted. The reasons for the post-
operative GHABP results not being present, was due to time constraints by the
audiologists administering test procedures.
Of the 17 implanted subjects whose pre-operative responses were analysed
compared to the short-term post-operative responses, 94% had nominated at
least one individual hearing difficulty. These nominated hearing difficulties were
particular to individuals with UPSHL as some of the subject responses included;
“to hear the passenger in the car if driving (left ear was affected ear)”, “listening
to music and hearing a stereo effect”, and “when talking on the telephone, being
able to hear another person in the room to relay a message”.
The results showed there was a statistically significant improvement in the
disability scores from the initial pre-operative disability score to the short-term
and long-term post-operative residual disability scores. This indicated a
146
treatment effect for this study’s implanted subjects. Niparko et al. (2003)
administered the GHABP with a comparison between the treatment of a CROS
aid and the BAHA across his ten subjects. The BAHA residual disability score
was reported as a mean and standard deviation of 34.4 ± 14.1. In this study,
the mean and standard deviations of the implanted subjects’ short-term and
long-term residual disability scores were 33.5 ± 12.7 and 37.5 ± 15.2,
respectively. Hence, there was similar mean and standard deviations to the two
studies. A comparison of all of the four scale scores of this study to Niparko et
al. (2003)’s study showed similar results as shown in Table 7.1.
A further two subjects’ responses were added in the analysis of the short-term
and long-term post-operative evaluation of the device (n=19). The results are
similar to Niparko et al. (2003)’s study, however the implanted subjects in this
study reported reduced long-term usage of their device. There was a significant
improvement between short-term and long-term use, benefit, and satisfaction
scale scores. These indicate that there was increased treatment effect over
time with this study.
Table 7.1 Comparison of implanted GHABP mean ± standard deviation of the four scale scores between two BAHA studies.
Study Residual disability
Use Benefit Satisfaction
Niparko et al. (2003) (n=10)
34.4 ± 14.1 80.9 ± 21.7 33.3 9 ± 21.5 32.3 ± 23.5
This study’s short-term
results (n=17)
33.5 ± 12.7
81.5 ± 14.4
50.0 ± 20.5
53.9 ± 19.6
This study’s long-term
results (n=19)
37.5 ± 15.2
69.3 ± 18.7
40.3 ± 20.5
45.2 ± 21.1
Note. Data from row 2 are from “Comparison of the bone anchored hearing aid implantable hearing device with contralateral routing of offside signal amplification in the rehabilitation of unilateral deafness.” By J. K. Niparko, K. M. Cox, & L. R. Lustig, 2003, Otology & Neurotology, 24(1), p.76.
147
7.5.3 SSDQ
In this study, only the subjects who were implanted completed the SSDQ post-
operatively. The subjects’ SSDQ results were analysed with two different time
frames, short-term (n=18) and long-term (n=13). Overall the long-term results
of the SSDQ showed high levels of subject satisfaction with the device and
excellent usage, i.e. daily use often for many hours per day. However, most
subjects reported no long-term definite ability to localise sounds.
Table 7.2 shows a comparison between the SSDQ results from the Wazen et al.
(2003) study, the Tringali et al. (2008) study and this study’s implanted group’s
short-term and long-term results. In the Wazen et al. (2003) study, 83% of the
subjects had a UPSHL following VS removal, whereas in this study only 28.5%
of the subjects had a UPSHL resulting from tumour removal. The Tringali et al.
(2008) study consisted of 118 subjects who were fitted with a BAHA for their
UPSHL. The authors reported that 78% of their subjects had a UPSHL
following VS or meningioma removal. This study also had two subject groups,
those fitted with BAHA for UPSHL, and a group of subjects fitted with a BAHA
for a conductive hearing loss (CHL). The authors compared and combined
results of these two groups; hence there are only partial results on Table 7.2.
This has been highlighted in the table to signify the results do not exclusively
reflect BAHA results as a treatment for UPSHL. Tringali et al. (2008) also used
an abridged version of the SSDQ, and therefore a direct comparison between
the three studies is only possible for selected parts of the SSDQ.
The average age of the implanted subject groups in the studies were similar:
50.61 years (Wazen et al., 2003), 56 years (Tringali et al., 2008), while this
study’s average age of subjects was 51 years. There were further similarities
between this study and the Wazen et al. (2003) study regarding the gender ratio
and length of deafness in this study’s subjects. This study’s implanted group
range for length of deafness was 0.2 to 39.3 years, compared to the Wazen et
al. (2003) study’s group of 0.5 to 27 years.
Subjects’ responses to the questionnaire were obtained three months post-
fitting in the Wazen et al. (2003) study, whilst this study’s short-term SSDQ
148
results shown on Table 7.2 were from three to six months post-fitting. In the
Tringali et al. (2008) study, responses were obtained from subjects an average
of 22 months post-fitting (range of 3 months to 72 months). The long-term
responses from the implanted subjects in this study are displayed on Table 7.2
and reflect an average of 18 months post-fitting (range 12 months to 36
months).
The results from the three groups were very similar. Direct comparison can be
made between the three study groups in relation to questions 4 and 7. The
Wazen et al. (2003) group had the highest rating for the reported aesthetic
appeal of the BAHA device. Differences were noted for BAHA usage between
the studies. Wazen et al. (2003)’s subject group wore their devices for more
days in the week and longer periods, compared to the number of subjects in this
study who wore their devices 5-6 days a week both in the short-term and long-
term surveys. The majority of the subjects in this study (54%) reduced their
daily use over the long-term to between 4-8 hours.
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Table 7.2
Summary of responses to single-sided deafness questionnaire (SSDQ) across studies.
Wazen et al. (n=17) Tringali et al. (n=118)
Implanted groups’ S-T responses (n=18)
Implanted groups’ L-T responses (n=13)
Question number
Question Possible responses
Dispersion of Responses
n % Dispersion of
responses
n % Dispersion of responses
n % Dispersion of
responses
n %
1
How many days/week do you use your
device?
7 days/week 5-6 days/week 3-4 days/week
12 4 1
70 24 6
6 11 1
33 61 6
5 6 2
38 46 15
2
How many hours per day do you use your
device?
More than 8 Between 4-8 Between 2-4 Less than 2
16 1 0 0
94 6 0 0
48.5 33 4
14.5
10 7 1 0
56 39 6 0
5 7 1 0
38 54 8 0
3
Has your quality of life improved?
Yes No
Mixed (Yes & No)
12 1 4
70 6 24
Average 6.35 13 1 4
72 6 22
9 0 4
69 0 31
4
Try to determine your satisfaction…
(10 point rating scale)
Average score Range
8 5 to 10
6.26 7.8 6 to 10
8.46 6 to 10
5.1
Talking to one person in a quiet situation
Better No difference
Worse Result missing
15 1 0 1
88 6 0 6
15 3 0
83 17 0
10 2 1
77 15 8
5.2
Talking to one person amongst a group?
Better No difference
Worse
15 1 1
88 6 6
15 3 0
83 17 0
8 3 2
62 23 15
5.3
Listening to music?
Better No difference
Worse
12 5 0
70 30 0
13 5 0
72 28 0
6 3 4
46 23 31
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Table 7.2 continued Question number
Question Possible Responses
Dispersion of Responses
N % Dispersion of
Responses
n % Dispersion of Responses
n % Dispersion of
Responses
n %
5.4
Listening to TV/radio?
Better No difference
Worse Result missing
14 3 0
82 8 0
14 4 0
78 22 0
7 3 2 1
54 23 15 8
5.5
At the dinner table?
Better No difference
Worse Result missing
15 2 0
88 12 0
16 1 0 1
89 6 0 6
9 0 4
69 0 31
6
Locating from where a
sound is coming?
Yes No
Mixed (Yes & No)
No difference Result missing
2 1 4 ?
12 6 24 ?
Average 4.85 3 6 7 1 1
17 33 39 6 6
0 8 4 1
0 62 31 8
7
How satisfied are you with the aesthetics?
(10 point rating scale)
Range
8.82 6 to 10
6.66 8.4 4 to 10
7.15 5 to 10
8
How do you find the
handling of the device?
Very easy Easy
Acceptable Difficult
8 5 4 0
47 29 24 0
7 10 1 0
39 56 6 0
5 6 2 0
38 46 15 0
Results highlighted in grey are a combination of CHL and UPSHL groups in the Tringali et al. (2008) study. S-T = short –term; L-T = long-term *Full copy of SSDQ in Appendix VII
Note. Data from column titled Wazen et al. are from “Transcranial contralateral cochlear stimulation in unilateral deafness.” by J. J. Wazen, et al., 2003, Otolaryngology-Head and Neck Surgery, 129(3), pp 248-254. Data from columns titled Tringali et al. are from “A survey of satisfaction and use among patients fitted with a BAHA.” by S. Tringali, et al., 2008, European Archives of Otorhinolaryngology, 265(12), pp 1461-1464.
151
Further comparisons can be made of the satisfaction rating between BAHA
users who have been implanted for traditional rehabilitation of conductive
hearing losses. In reference to satisfaction ratings, using the same rating
system as the SSDQ, Tjellstrom and Hakansson (1995) reported that in a study
of 127 BAHA users, an overall satisfaction score of 8.7 on the rating scale was
given. This was higher than the reported satisfaction ratings for the three
studies on BAHA for UPSHL using the SSDQ as shown in Table 7.2. Tjellstrom
& Hakansson (1995)’s study with the higher rating by their BAHA users may be
related to their subjects’ previous experience with BCHAs and the amount of
otolaryngological intervention required for the conductive component of their
hearing loss, particularly if the subjects had persistent discharging ears.
7.5.4 BAHA outcome measures with non-implanted subjects
The APHAB and GHABP were readministered at the same time to all the non-
implanted subjects, therefore the period of time since their pre-operative
assessment ranged from 6 months to four years and seven months. The
average time for the group was two years and seven months.
The second administration of the APHAB to the 22 subjects who were not
implanted showed no significant change in their pre-operative subscale scores
when compared to their second set of subscale scores, although there was a
large spread of in the scores as indicated by the large standard deviations.
Similarly, results from the GHABP readministration to the same group of 21
non-implanted subjects showed no significant difference in the scale scores to
the first administration. As for the APHAB, there was a wide range of
responses for both sets of surveys, as shown for the high values for the
standard deviations.
These results were expected, as these subjects had not undergone treatment
by a fitting of a BAHA device. The wide fluctuation in scores of this non-
implanted group may be due to multi-factorial issues such as personality,
coping strategies, or different work situations and demands on hearing in their
everyday activities. There were several subjects who had only had their loss for
152
a short amount of time prior to their pre-operative assessment. Based on the
authors’ clinical experience, over time some individuals with a hearing loss will
acclimatise to that particular loss and develop strategies to compensate for the
hearing loss.
There was a mixed response in the status of subjects who had their hearing
loss less than two years, with some reporting an increase whilst others reported
a decrease in their hearing difficulties. Sargent et al. (2001) reported that
subjects with longer duration of unilateral hearing impairment may experience
auditory deprivation similar to that of individuals with bilateral SNHL but only
hearing by wearing one hearing aid. They found that these subjects’ speech
discrimination ability decreases over time in the unaided ear, despite their
hearing thresholds remaining symmetrical and no change in speech
discrimination ability in the aided ear.
The non-implanted subjects responses to the APHAB administration during the
pre-operative assessment indicated reported that hearing in background noise,
which is highlighted in the BN subscale of the APHAB, caused the greatest
hearing difficulty. This subscale continued to have the highest percentage of
reported difficulty, when these subjects were reassessed with the APHAB some
time after the pre-operative assessment. Seventy-seven percent of these
subjects’ scores were highest for the BN subscale.
7.6 Limitations to the study
There were a number of limitations to this study. There was an evolvement of
the BAHA during the course of the study, meaning that assessment of
outcomes could only be made for the BAHA and not individual devices and
models. The primary problem encountered by this study has already been
discussed previously was the difficulty in developing a speech testing protocol
suitable for this hearing loss group.
Finally, as the device evolved and ownership of the device changed from Entific
to Cochlear Limited, there was development in the candidacy and fitting
protocols, as well as literature for counselling subjects about expectations
153
regarding a BAHA for UPSHL. Snik et al. (2005) discussed that due to the
BAHA being fitted on the impaired side, the device had to cooperate with the
normal ear. They suggested that the powerful BAHA Classic may be a better
choice than the Compact model. Following this logic, the device with greater
power should be used on the headband during the trial period. It is possible
that all subjects in this study should have been given the Classic 300 or Intenso
as the test device instead of the Compact or Divino model. Unfortunately this
was not possible in all cases due to a limited number of test devices.
7.7 Future studies
Although two subjects with congenital UPSHL were included in this study, the
small subject numbers means that there is limited scope to make significant
findings. Furthermore, there was a small sample of subjects with an acquired
UPSHL under 12 years of age. One of these subjects was implanted and
showed significant benefit from wearing the device. A study examining the
localisation abilities of BAHA users who acquire their UPSHL hearing loss
before and after the critical period in acquisition of binaural cues would be give
greater insight to whether there were any influences on early onset hearing loss
influences outcomes with the BAHA.
Another study could be to examine whether a BAHA fitting can provide the
same benefit for adults with a congenital unilateral hearing loss as that achieved
by an adult with an acquired unilateral hearing loss. As a greater understanding
of the impact of UPSHL on social and academic outcomes is explored, it will be
reasonable to enquire further as to whether a BAHA should be fitted to a child
with a UPSHL. If improvement were evident, this would advocate the
introduction of BAHA as a rehabilitation tool for children with UPSHL to help
improve their general hearing abilities and possibly academic performance in
the presence of background classroom noise. Larger studies of adult subjects
with congenital or early-acquired UPSHL would need to be conducted to give
definitive answers to these questions.
Further studies comparing the BAHA to wireless CROS systems to this subject
group of UPSHL are warranted to ascertain respective advantages of these
154
different treatment options. Previous studies comparing BAHA to CROS
hearing aid fittings have been limited in their details regarding what type of
CROS devices were fitted (Baguley et al., 2006). Technology in the area of
CROS hearing aids has also improved with many more wireless frequency
modulated CROS systems available in the last few years.
A study on the fitting of FM systems compatible with the BAHA, such as the
Microlink FM system (Phonak Hearing Solutions) to subjects with BAHAs for the
treatment of UPSHL could guide in whether these accessories should be fitted
to this population of BAHA users routinely. There have been no studies to date
looking at the outcomes for individuals fitted with an FM system and a BAHA
device. One of the implanted subjects, whose occupation is a principal of a
primary school, has reported positive results when he uses the Microlink
receiver with a FM transmitter connected to his BAHA sound processor.
Use of the BAHA Intenso model was not examined as its introduction to the
market was during the later stages of this study. Two of the implanted subjects
in the study have since been fitted with the Intenso model and reported positive
feedback. The use of this stronger ear level sound processor in the pre-
operative testing on the test band and trial stage needs further evaluation.
There have been reports that individuals with UPSHL may require a stronger
Intenso rather than the Divino model due to the interaural attenuation of bone
conduction (Flynn, 2008). Presently, there are no guidelines on which subjects
this applies to, so further study in this area is required to ensure those who are
implanted are fitted with the correct sound processor model.
All the reporting in this study was with the subjects using a BAHA on an
omnidirectional microphone. Studies could compare the subjects’ ability with
directional microphones. A directional microphone is available as an accessory
with the Compact model, but is in-built in the Divino model. The use of a
directional microphone may improve their subjects’ ability to hear in the
presence of background to a greater extent than shown with the omnidirectional
setting on both the Compact and Divino models. Therefore, subjects trialling
stronger BAHA devices with directional microphone may find the device has
155
greater benefit and increase the uptake of BAHA for UPSHL. However,
currently there is no powerful BAHA sound processor such as the Intenso with
an in-built directional microphone available.
These suggested further studies will enable audiologists, otolaryngologists,
educational and other health providers an ability to re-evaluate their practises to
improve outcomes for those individuals with a UPSHL.
156
Chapter 8: Conclusions This study examined the UPSHL subjects’ speech perception in quiet and
noise. The subjects were evaluated pre-operatively with the BAHA on a test
band to determine whether there was a difference in the presentation levels or
SNR required compared to the unaided condition. Due to several modifications
in test protocols during the course of the study, no significant conclusion could
be made, as the number of comparable results was too small to test for
statistical significance.
Speech testing was part of the test protocol to compare results with outcome
measures in order to determine which subjects with a UPSHL were better
candidates than others to receive a BAHA device. There was limited data to do
correlations to compare speech testing results to those of the data obtained
from the outcome measures. Therefore this aim was not achieved.
However, this study was able to show a treatment effect when fixed
presentation levels of testing in quiet were assessed pre- and post-operatively.
This was also reflected in the outcome measures with implanted subjects
reporting benefit when wearing the device in quiet listening situations. This
suggests hearing monaurally may cause fatigue, and that hearing in quiet with
individuals with UPSHL is a greater issue than reported in the literature.
This study evaluated the short-term and long-term quality of life outcomes of
BAHA implantation using the three questionnaires, the APHAB, GHABP and
SSDQ. There was a significant difference between the implanted groups’ pre-
and post-operative outcome measures in all three questionnaires, indicating a
treatment effect of the fitting of the BAHA device.
The post-operative questionnaire results showed there was depreciation over
time in the reported overall usage and satisfaction rates of the implanted
subjects. However, they remained significantly higher than their pre-operative
scores.
157
The APHAB and GHABP questionnaires were readministered to the non-
implanted subject group to evaluate their long-term outcomes. No significant
changes were found. The results showed that over time, these subjects had the
same level of hearing difficulties as they had originally reported at their initial
assessment. Despite this, only 4.5% of the group who responded to the second
survey had been fitted with another form of intervention, i.e. a WiFi CROS aid
and reported benefit.
No significant correlations were found between outcome measures and gender,
length of profound hearing loss, age of fitting, or ear affected for either the
implanted or non-implanted group.
The implanted subjects were monitored for abutment and repair issues
regarding their BAHA system. Although there were a high number of skin
reactions around the abutment that required treatment (38%), as well as two-
thirds of the subjects having repairs on their external device, this did not affect
the perceived benefit of the device in most cases. Eighty-one percent of
subjects continued to use their BAHA device long-term. Four implanted
subjects had stopped using their device during the study - three due to reported
insufficient benefit from their BAHA model, whilst one had persistent pain
associated with the abutment.
The main reason that subjects did not undergo implantation was the lack of
sufficient benefit from the trial device. The trial device in this study was a
Compact or Divino model in most cases. However, subjective feedback from
UPSHL subjects who have trialled the more powerful ear level device, the
Intenso, reported that greater benefit is perceived with the stronger device.
Hence, the trial device needs to be the powerful ear level model, which may
lead to a greater uptake in BAHA for UPSHL.
This study’s results revealed that the majority of the implanted subjects with
UPSHL continue to wear their BAHA several years post-fitting and receive
continued benefit. Thus surgical implantation of the BAHA remains one of the
158
treatment methods of choice for the hearing rehabilitation with subjects with
UPSHL.
159
Chapter 9: References Abrams, H. B. (2000). Outcome measures in audiology: Knowing that we've
made a difference. Audiology Online. Retrieved from
http://www.audiologyonline.com/articles/article_detail.asp?article_id=236
Acoustic Neuroma Association (NSW). (2005). Australian acoustic neuroma
statistics. Retrieved January 22, 2009, from
http://www2.tpgi.com.au/users/bcrowe/statistics.htm
Australian Hearing. (1997, May). Completely-in-the-canal (CIC) candidacy.
Paper presented at Australian Hearing In-house training, Perth, Western
Australia.
Australian Hearing. (2000). National acoustic laboratories (NAL) speech and
noise for hearing aid evaluation manual and compact disk (CD).
Chatswood, New South Wales: Author.
Australian Hearing. (2008a). Degrees of hearing loss. Retrieved October 28,
2008, from
http://www.hearing.com.au/ViewPage.action?siteNodeId=45&languageId
=1&contentId=-1
Australian Hearing. (2008b). Options for children with a unilateral hearing loss.
Retrieved October 28, 2008 from
http://www.hearing.com.au/digitalAssets/5960_1208217448679_options-
unilateral-hearing-loss.pdf
Badran, K., Arya, A. K., Bunstone, D., & Mackinnon, N. (2009). Long-term
complications of bone-anchored hearing aids: A 14-year experience. The
Journal of Laryngology & Otology,123(2), 170-176.
Baguley, D. M., Bird, J., Humphriss, R. L., & Prevost, A. T. (2006). The
evidence base for the application of contralateral bone anchored hearing
160
aids in acquired unilateral sensorineural hearing loss in adults. Clinical
Otolaryngology, 31(1), 6-14.
Barr, M. L., & Kiernan, J. A. (1988). The human nervous system - An
anatomical viewpoint. (5th ed.). Philadelphia: JP Lippincott Company.
Bellis, T. J. (2003). Assessment and management of central auditory
processing disorders in the educational setting: From science to practice.
(2nd ed.). New York: Delmar Learning.
Bench, J., & Doyle, J. (1979). The BKB/A (Bamford-Kowal-Bench/Australian
version) sentence lists for hearing-impaired children. Bundoora, Victoria:
Author.
Bench, J., Kowal, A., & Bamford, J. (1979). The BKB (Bamford-Kowal-Bench)
sentence lists for partially-hearing children. British Journal of Audiology,
13, 108-112.
Bentler, R. (2000). Amplification for the hearing-impaired child. In J. Alpiner & P.
McCarthy (Eds.), Rehabilitative audiology: Children and adults (3rd ed.,
pp. 106-139). Baltimore: Lippincott Williams & Wilkins.
Bentler, R. A. (2006, 13-15 November). Audiometric considerations for hearing
aid fittings (and success). Paper presented at the Hearing Care for
Adults: An International Conference, Chicago, USA. Retrieved February
12, 2009, from
https://www.phonak.com/authorized/de/print/chicago2006_day-1_7.pdf
Bentz, B. G. (2008). Barotrauma. Retrieved April 28, 2009, from
http://www.american-hearing.org/disease/barotrauma.html
Bess, F. H., Rothpletz, A. M., & Dodd-Murphy, J. (2002). Children with unilateral
sensorineural hearing loss. In V. E. Newton (Ed.), Paediatric audiological
medicine (pp. 294-313). London: Whurr Publishers Ltd.
161
Bess, F. H., & Tharpe, A. M. (1986). An introduction to unilateral sensorineural
hearing loss in children. Ear & Hearing, 7(1), 3-13.
Bosman, A. J., Hol, M. K., Snik, A. F., Mylanus, E. A., & Cremers, C. W. (2003).
Bone-anchored hearing aids in unilateral inner ear deafness. Acta Oto-
Laryngologica, 123(2), 258-260.
Brackman, D. E., & Green, J. D. (2008). Transbyrinthine approach for acoustic
tumor removal. Neurosurgery Clinics of North America, 19(2), 251-264.
Breitholtz, F. (2008). The benefits of bilaterally fitting a baha. Implantable
Hearing Solutions, 2, 11-13.
Brice, R. (1998). Figure 1-Duplex hearing theory [image]. Retrieved February
24, 2009, from http://www.classicproaudio.com/franci_revisited.htm
Burkey, J. M., Berenholz, L. P., & Lippy, W. H. (2006). Latent demand for the
bone-anchored hearing aid: The Lippy group experience. Otology &
Neurotology, 27(1), 648-652.
Burrell, S. P., Cooper, H. C., & Proops, D. W. (1996). The bone anchored
hearing aid - The third option for otosclerosis. The Journal of
Laryngology & Otology, 110, BAHA Supplement, 31-37.
Byrne, D., Noble, W., & LePage, B. (1992). Effects of long-term bilateral and
unilateral fitting of different hearing aid types on the ability to locate
sounds. Journal of American Academy of Audiology, 3, 369-382.
Byrne, D. J., Noble, W., & Sinclair, S. (1996). High fidelity hearing aid for
improving sound localisation. Chatswood: National Acoustic Laboratories
Annual Report 1996/97.
Center for Hearing and Communication. (2008). Understanding the audiogram
[image]. Retrieved January 15, 2009, from
http://www.lhh.org/about_hearing_loss/understanding/audiogram.html
162
Ching, T. Y. C., Incerti, P., Hill, M., & Brew, J. (2004). Bimodal hearing: A guide
to fitting (No. N30495F ISSI MAY04). Chatswood, New South Wales:
Australian Hearing.
Chiossoine-Kerdel, J. A., Baguley, D. M., Stoddart, R. L., & Moffat, D. A. (2000).
An investigation of the audiological handicap associated with unilateral
sudden sensorineural hearing loss. The American Journal of Otology,
21(5), 645-651.
Cochlear Limited. (2005). Baha Divino - A personal experience brochure.
Goteborg, Sweden: Entific Medical Systems.
Cochlear Limited. (2008a). Baha Divino [image]. Retrieved January 21, 2009,
from http://www.cochlear.com.au/Products/927.asp
Cochlear Limited. (2008b). Baha Intenso [image]. Retrieved January 21, 2009,
from http://www.cochlear.com.au/Products/2472.asp
Cochlear Limited. (2008c). Baha timeline [image]. Foundations of Baha-
Audiology paper presented at in-service training. Perth: Cochlear
Limited.
Colletti, V., Fiorino, F. G., Carner, M., & Rizzi, R. (1988). Investigation of the
long-term effects of unilateral hearing loss in adults. British Journal of
Audiology, 22, 113-118.
Cooper, H. R., Burrell, S. P., Powell, R. H., Proops, D. W., & Bickerton, J. A.
(1996). The Birmingham bone anchored hearing aid programme:
Referrals, selection, rehabilitation, philosophy and adult results. The
Journal of Laryngology and Otology, 110, BAHA Supplement, 13-20.
Cox, R. M. (1996). The abbreviated profile of hearing aid benefit (APHAB)-
administration and application. Retrieved from Phonak Focus
News/Ideas/High Technology/Acoustics No 21, 1-16.
163
Cox, R. M. (1997). Administration and application of the APHAB. The Hearing
Journal, 50(4), 32-48.
Cox, R. M., & Alexander, G. C. (1995). The abbreviated profile of hearing aid
benefit. Ear & Hearing, 16, 176-186.
Culbertson, J. L., & Gilbert, L. E. (1986). Children with unilateral sensorineural
hearing loss. Ear and Hearing, 7(1), 38-42.
Davids, T., Gordon, K. A., Clutton, D., & Papsin, B. C. (2007). Bone-anchored
hearing aids in infants and children younger than 5 years. Archives of
Otolaryngology - Head & Neck Surgery, 133(1), 51-55.
Davis, P., Pogash, R., Engelund, G., Arslan, E., Philips, A., Lutman, M., et al.
(2001, September). Pediatric clinical trial of a non-linear hearing aid for
severe hearing losses: Repeated speech intelligibility measures. Paper
presented at the 5th European Federation of Audiological Societies
(EFAS) Congress, Bordeaux, France.
Dillon, H. (2001). Hearing aids. Sydney, New South Wales: Boomerang Press.
Dillon, H., & Ching, T. Y. C. (1995). What makes a good speech test? In G.
Plant & K.-E. Spens (Eds.), Profound deafness and speech
communication (pp. 305-343). London: Whurr Publishers Ltd.
Dillon, H., James, A., & Ginis, J. (1997). Client orientated scale of improvement
(COSI) and its relationship to several other measures of benefit and
satisfaction provided by hearing aids. Journal of the American Academy
of Audiology, 8, 27-43.
Ear Technology Corporation. (2008). Dry & store [image]. Retrieved March 31,
2009, from
http://www.dryandstore.com/?BISKIT=2719856398&CONTEXT=cat&cat
=15
164
Edwards, C. G., Schwartzbaum, J. A., Lonn, S., Ahlbom, A., & Feychting, M.
(2006). Exposure to loud noise and risk of acoustic neuroma. American
Journal of Epidemiology, 163(4), 327-333.
Entific Medical Systems. (2000). Bone Anchored Applications, 01/2000.
Goteborg, Sweden: Author.
Entific Medical Systems. (2001). Audiological manual: Selection criteria,
evaluation and fitting procedures for baha. Goteborg, Sweden: Author.
Entific Medical Systems. (2003a). Audiological manual: Selection criteria,
evaluation and fitting procedures for baha. Goteborg, Sweden: Author.
Entific Medical Systems. (2003b). Introducing baha for single sided deafness:
Hear the other side [Brochure]. Goteborg, Sweden: Author.
Entific Medical Systems. (2005a). Baha CROS [image]. Retrieved July 31,
2005, from http://www.entific.com
Entific Medical Systems. (2005b). Classic 300 side view [image]. Retrieved
October 20, 2005, from http://www.entific.com
Entific Medical Systems. (2005c). Compact [image]. Retrieved August 31, 2005,
from http://www.entific.com
Entific Medical Systems. (2005d). Surgical manual [image]. Retrieved July 18,
2005, from http://www.entific.com
Entific Medical Systems. (2005e). Test rod [image]. Retrieved July 31, 2005,
from www.entific.com.au
Falcone, M. T., & Labadie, R. F. (2007). An alternative approach for surgical
dressing of bone-anchored hearing aid abutment sites. The
Laryngoscope, 117(4), 614-616.
Ferraro, J. A. (2003). Clinical electrocochleography: Overview of theories,
techniques and applications. Audiology Online. Retrieved from
165
http://www.audiologyonline.com/Articles/pf_article_detail.asp?article_id=
452
Feuerstein, J. F. (1992). Monaural versus binaural hearing: Ease of listening,
word recognition and attentional effort. Ear & Hearing, 13(2), 80-86.
Fisch, L. (1983). Integrated development and maturation of the hearing system.
British Journal of Audiology, 17, 137-154.
Flynn, M. (2008). Overcoming hearing loss with the baha system (No. E81038A
JUNO8). Sydney, New South Wales: Cochlear Limited.
Forton, G. E., Cremers, C. W., & Offeciers, F. E. (2004). Acoustic neuroma in
growth in the cochlear nerve: Does it influence the clinical presentation?
Annals of Otology, Rhinology & Laryngology, 113, 582-586.
Fowler, C. G.& Shanks, J. E. (2001). Tympanometry. In J. Katz (Ed.), Handbook
of clinical audiology (5th ed., pp. 175-204). Baltimore: Lippincott Williams
& Wilkins.
Fowler, K. B., McCollister, F. P., Dahle, A. J., Boppana, S., Britt, W. J., & Pass,
R. F. (1997). Progressive and fluctuating sensorineural hearing loss in
children with asymptomatic congenital cytomegalovirus infection. The
Journal of Pediatrics, 130, 624-630.
Gatehouse, S. (1999). Glasgow hearing aid benefit profile: Deviation and
validation of client-centred outcome measures for hearing aid services.
Journal of the `American Academy of Audiology, 10, 80-103.
Ghossaini, S. N. (2006). The baha (bone anchored hearing aid). Retrieved
October 28, 2008, from http://www.american-
hearing.org/disorders/hearing/baha.html
Gibson, W. (2003). Meniere's disease. Retrieved March 21, 2009, from
http://www.healthinsite.gov.au/expert/Meniere_s_Disease
166
Goycoolea, M. V., Iniguez, R., & Perez, M. (1995). Diseases of the ear:
Acquired diseases. In C. de Souza, M. V. Goycoolea & C. B. Ruah
(Eds.), Textbook of the ear, nose & throat (pp. 71-77): London: Orient
Blackswan.
Grant, P. (1999). Sensorineural hearing loss. Retrieved November 1, 2008,
from www.medicineau.net.au/clinical/ent/SNHL.html
Hakansson, B. (2006). Figure 5: Principle design of a single housing baha
[image]. Retrieved October 12, 2008, from http://www.baha-users-
support.com/birth_of_baha_p5.php
Hakansson, B., Eeg-Olofsson, M., Reinfeldt, S., Stenfelt, S., & Granstrom, G.
(2008). Percutaneous versus transcutaneous bone conduction implant
system: A feasibility study on a cadaver head. Otology & Neurotology,
29(8), 1132-1139.
Hakansson, B., Liden, G., Tjellstrom, A., Ringdahl, A., Jacobsson, M., Carlsson,
P., et al. (1990). Ten years experience with the Swedish bone-anchored
hearing system. Annals of Otology, Rhinology & Laryngology, 151, 1-16.
Hakansson, B., Tjellstrom, A., & Rosenhall, U. (1984). Hearing thresholds with
direct bone conduction versus conventional bone conduction.
Scandinavian Audiology, 13, 3-13.
Hall, J. W., & Mueller, H. G. (1997). Audiologists' desk reference: Volume II.
San Diego, California: Singular Publishing Group, Inc.
Hayes, D. E., & Chen, J. M. (1998). Bone-conduction amplification with
completely-in-the canal hearing aids. Journal of American Academy of
Audiology 9, 59-66.
Hill, S. L., Marcus, A., Digges, E. N. B., Gillman, N., & Silverstein, H. (2006).
Assessment of patients’ satisfaction with various configurations of digital
167
CROS and BiCROS hearing aids. Ear, Nose & Throat Journal, 85(7),
427-30, 442.
Hol, M. K., Bosman, A. J., Snik, A. F., Mylanus, E. A., & Cremers, C. W.
(2004a). Bone-anchored hearing aid in unilateral inner ear deafness: A
study of 20 patients. Audiology & Neuro-Otology, 9(5), 274-281.
Hol, M. K., Bosman, A. J., Snik, A. F., Mylanus, E. A., & Cremers, C. W. (2005).
Bone-anchored hearing aids in unilateral inner ear deafness: An
evaluation of audiometric and patient outcome measurements. Otology &
Neurotology, 26(5), 999-1006.
Hol, M. K. S., Spath, M. A., Krabbe, P. F., van der Pouw, C. M., Snik, A. F.,
Cremers, C. W., et al. (2004b). The bone-anchored hearing aid: Quality-
of-life assessment. Archives of Otolaryngology - Head & Neck Surgery
130(4), 394-399.
Holgers, K. M., Tjellstrom, A., Bjursten, L. M., & Erlandsson, B. E. (1987). Soft
tissue reaction around percutaneous implants: A clinical study on skin-
penetrating titanium implants used for bone-anchored auricular
prostheses. International Journal of Oral Maxillofacial Implants, 2, 35-39.
House, J. W., & Kutz, J. W. (2007). Bone-anchored hearing aids: Incidence and
management of postoperative complications. Otology & Neurotology,
28(2), 213-217.
Humphriss, R. L., Baguley, D. M., Axon, P. R., & Moffat, D. A. (2006).
Preoperative audiovestibular handicap in patients with vestibular
schwannoma. Skull Base, 16(4), 193-199.
Ito, K., Endo, A., Monobe, H., Ochiai, A., & Iwasaki, S. (2005). Nonsyndromic
isolated unilateral cochlear nerve aplasia without narrow internal auditory
meatus: A previously overlooked cause of unilateral profound deafness
168
in childhood. Annals of Otology, Rhinology & Laryngology, 114(11), 859-
862.
Jia, H., Marzin, A., Dubreuil, C., & Tringali, S. (2008). Intralabyrinthine
schwannomas: Symptoms and management. Auris Nasus Larynx, 35(1),
131-136.
Keidser, G., Ching, T., C., Dillon, H., Agung, K., Brew, C., Brewer, S., et al.
(2002). The national acoustic laboratories' (NAL) CDs of speech and
noise for hearing aid evaluation: Normative data and potential
applications. The Australian and New Zealand Journal of Audiology, 24
(1), 16-35.
Killion, M. C. (1997a). SNR loss: "I can hear what people say, but I can't
understand them". The Hearing Review, 4(12), 8-14.
Killion, M. C. (1997b). The SIN report: Circuits haven't solved the hearing-in-
noise problem. The Hearing Journal, 50(10), 28-32.
Kiyomizu, K., Matsuda, K., Nakayama, M., Tono, T., Matsuura, K., Kawano, H.,
et al. (2006). Preservation of the auditory nerve function after
translabyrinthine removal of vestibular schwannoma. Auris Nasus
Larynx, 33(1), 7-11.
Kohan, D., Morris, L., & Romo, T. (2008). Single-stage baha implantation in
adults and children: Is it safe? Otolaryngology - Head and Neck Surgery,
138, 662-666.
Krishnaswamy, J. (2008, November). Newborn screening update. Paper
presented at the Western Australian branch continuing professional
development day at Perth, Western Australia.
Lekakis, G. K., Najuko, A., & Gluckman, P. G. (2005). Wound related
complications following full thickness skin graft versus split thickness skin
169
graft on patients with bone anchored hearing aids. Clinical
Otolaryngology, 30, 324-327.
Lin, L., Bowditch, S., Anderson, M. J., May, B., Cox, K. M., & Niparko, J. K.
(2006). Amplification in the rehabilitation of unilateral deafness: Speech
in noise and directional hearing effects with bone-anchored hearing and
contralateral routing of signal amplification. Otology & Neurotology,
27(2), 172-182.
Litovsky, R. (2007). Potential advantages from bilateral cochlear implants
[Brochure]. Sydney, NSW: Cochlear Limited.
Macnamara, M., Phillips, D., & Proops, D. W. (1996). The bone anchored
hearing aid (BAHA) in chronic suppurative otitis media (CSOM). The
Journal of Laryngology & Otology, 110 (BAHA supplement), 38-40.
Mahmud, M. R., Khan, A. M., & Nadol, J. B. (2003). Histopathology of the inner
ear in unoperated acoustic neuroma. Annals of Otology, Rhinology &
Laryngology, 112, 979-986.
Man-Wook Seo. (2007). Acoustic tumor [image]. Retrieved January 18, 2009,
from http://js-dizz.com/page/innerear/images/acoustic_tumor1.jpg
Maroon, J. (2005). Skull-base surgery: Past, present, and future trends.
Neurosurgicial Focus 19(1), 1-4.
McLeod, B., & Upfold, L. (1999). How deaf are our hearing aid
clients/patients/customers/markets? The Australian and New Zealand
Journal of Audiology, 21(2), 77-81.
McLeod, B., Upfold, L., & Taylor, A. (2008). Self reported hearing difficulties
following excision of vestibular schwannoma. International Journal of
Audiology, 47, 420-430.
170
Medical Research Council, Institute of Hearing Research (2005). IHR Products
Glasgow hearing aid benefit profile (GHABP). Retrieved January 13,
2005, from http://www.ihr.mrc.ac.uk/products/index.php?page=12
Medical Research Council, Institute of Hearing Research. (2008). Test materials
- Arthur Boothroyd word lists AB (S) Retrieved January 21, 2008,
http://www.ihr.mrc.ac.uk/products/index.php?page=15
Mo, B., Harris, S., & Lindbaek, M. (2004). Cochlear implants and health status:
A comparison with other hearing-impaired patients. Annals of Otology,
Rhinology & Laryngology, 113, 914-921.
Moore, B. C. (2003). An introduction to the psychology of hearing (3rd ed.).
Boston: Academic Press.
Mylanus, E. A. (1994). The bone anchored hearing aid: Clinical and audiological
aspects. Nijmegen, Nederlands:B. V. Boekdrukkerij F.E. MacDonald
Publishing.
Mylanus, E. A., Snik, A. F., & Cremers, C. W. (1994). The influence of the
thickness of the skin and subcutaneous tissue covering the mastoid on
bone conduction thresholds obtained transcutaneously versus
percutaneously. Scandinavian Audiology, 23, 201-203.
Mylanus, E. A., van de Pouw, K. C. T. M., Snik, A. F., & Cremers, C. W. (1998).
Intraindividual comparison of the bone-anchored hearing aid and air-
conduction hearing aids. Archives of Otolaryngology - Head & Neck
Surgery, 124(3), 271-276.
Nageris, B. J., Popovtzer, A., & Tiqva, P. (2003). Acoustic neuroma in patients
with completely resolved sudden hearing loss. Annals of Otology,
Rhinology & Laryngology, 112, 395-397.
171
Newman, C. W., Sandridge, S. A., & Wodzisz, L. M. (2008). Longitudinal benefit
from and satisfaction with the baha system for patients with acquired
unilateral sensorineural hearing loss. Otology & Neurotology, 29(8),
1123-1131.
Niparko, J. K., Cox, K. M., & Lustig, L. R. (2003). Comparison of the bone
anchored hearing aid implantable hearing device with contralateral
routing of offside signal amplification in the rehabilitation of unilateral
deafness. Otology & Neurotology, 24(1), 73-78.
Obholzer, R. J., Rea, P. A., & Harcourt, J. P. (2004). Magnetic resonance
imaging screening for vestibular schwannoma: Analysis of published
protocols. The Journal of Laryngology & Otology, 118(1), 329-332.
Olschwang, S. (2002). Neurofibromatosis type II. Orphanet encyclopedia, April
2002,1-2. Retrieved from http://www.orpha.net/data/patho/GB/uk-NF2
Parkin, A. J. (2000). Essential cognitive psychology: East Sussex: Psychology
Press Ltd.
Perez, C. M., Rodriguez, M. M., Macias, A. R., & Garcia-Ibanez, L. (2004). The
benefits of bimodal stimulation, a Spanish multi-centre study. Sydney,
NSW: Cochlear Limited.
Peters, B. R. (2007). Rationale for bilateral cochlear implantation in children and
adults. Sydney, NSW: Cochlear Limited.
Phonak Limited. (2009). Transmitters [image]. Retrieved January 21, 2009,
from http://www.phonak.com/com/b2c/en/products/fm/transmitters.html
Plomp, R. (1986). A signal-to-noise ratio model for the speech-reception
threshold of the hearing impaired. Journal of Speech and Hearing
Research, 29, 146-154.
172
Ponton, C. W., Vasama, J.-P., Tremblay, K., Khosla, D., Kwong, B., & Don, M.
(2001). Plasticity in the adult human central auditory system: Evidence
from late-onset profound unilateral deafness. Hearing Research, 154(1-
2), 32-44.
Pulec, J. (1994). Restoration of binaural hearing with the Audiant implant
following acoustic neuroma surgery. Ear Nose & Throat Journal, 73(2),
118-123.
Roberts, C., Mitchell, N., & Parker, J. (2005). Cochlear limited acquisition of
Entific Medical Systems AB investor briefing materials 04 March 2005,
Cochlear Limited Annual Report 2005 [Electronic version]. Retrieved July
21, 2006, from http://www.cochlear.com/assets/pdf/AR05_editorial.pdf
Robinson, K., Gatehouse, S., & Browning, G. (1996). Measuring patient benefit
from otorhinolaryngological surgery and therapy. Annals of Otology,
Rhinology & Laryngology, 105(6), 415-422.
Ruckenstein, M. J. (2000). Practical issues with the management of the dizzy
and balance disordered patient. Otolaryngologic Clinics of North
America, 33(3), 535-562.
Saeed, S. R., Birzgalis, A. R., & Ramsden, R. T. (1994). Intralabyrinthine
schwannoma shown by magnetic resonance imaging. Neuroradiology,
36, 63-64.
Sargent, E. W., Herrmann, B., Hollenbeak, C. S., & Bankaitis, A. E. (2001). The
minimum speech test battery in profound unilateral hearing loss. Otology
& Neurotology, 22(4), 480-486.
Sataloff, R. T., & Sataloff, J. (1993). Hearing loss , revised and expanded (3rd
ed). New York: Informa Health Care.
173
Schum, D. J., & Beck, D. L. (2008). Negative synergy: Hearing loss and aging:
Retrieved June 21, 2009 from
http://www.oticonusa.com/eprise/main/SiteGen/Uploads/Public/Download
s_Oticon/Audiology_Online/Negative_Synergy.pdf
Shanker, V., Davison, T., & Johnson, I. (2004). Glasgow benefit inventory (GBI)
in single sided deafness using baha. Bone Anchored Applications,1/04,
7-9. Goteborg, Sweden: Entific Medical Systems.
Sindhusakea, D., Mitchell, P., Smith, W., Golding, M., Newall, P., Hartley, D., et
al. (2001). Validation of self-reported hearing loss: The Blue Mountains
hearing study International Journal of Epidemiology, 30, 1371-1378.
Smits, C., Kramer, S. E., & Houtgast, T. (2006). Speech reception thresholds in
noise and self-reported hearing disability in a general adult population.
Ear & Hearing, 27(5), 538-549.
Snik, A. F., Beynon, A. J., Mylanus, E. A., Van der Pouw, C. M., & Cremers, C.
W. (1998a). Binaural application of the bone-anchored hearing aid. The
Annals of Otology, Rhinology & Laryngology, 107(3), 187-193.
Snik, A. F., Bosman, A. J., Mylanus, E. A., & Cremers, C. W. (2004). Candidacy
for the bone-anchored hearing aid. Audiology & Neuro-Otology, 9, 190-
196.
Snik, A. F., Dreschler, W. A., Tange, R. A., & Cremers, C. W. (1998b). Short
and long-term results with implantable transcutaneous and percutaneous
bone-conduction devices. Archives of Otolaryngology - Head & Neck
Surgery, 124(3), 265-268.
Snik, A. F., Mylanus, E. A. M., Proops, D. W., Wolfaardt, J., Hodgetts, W. E.,
Somers, T., et al. (2005). Consensus statements on the baha system:
174
Where do we stand at present? Annals of Otology, Rhinology &
Laryngology, 114(12), 1-12.
Spitzer, J. B., Ghossaini, S. N., & Wazen, J. J. (2002). Evolving applications in
the use of bone-anchored hearing aids. American Journal of Audiology,
11(2), 96-103.
Spriet, A., Van Deun, L., Eftaxiadis, K., Laneau, J., Moonen, M., van Dijk, B., et
al. (2007). Speech understanding in background noise with the two-
microphone adaptive beam former in the nucleus freedom cochlear
implant system. Ear & Hearing, 28(1), 62-73.
Stahl, N., & Cohen, D. (2006). Idiopathic sudden sensorineural hearing loss in
the only hearing ear. Archives of Otolaryngology - Head & Neck Surgery,
132(2), 193-195.
Stalfors, J., & Tjellstrom, A. (2008). Skin reactions after baha surgery: A
comparison between the u-graft technique and the baha dermatome.
Otology & Neurotology, 29(8), 1109-1114.
Starr, A., Picton, T. W., Sininger, Y., Hood, L. J., & Berlin, C. I. (1996). Auditory
neuropathy. Brain, 119(3), 741-753.
Stattery, W. H., & Middlebrooks, J. C. (1994). Monaural sound localization:
Acute versus chronic unilateral impairment. Hearing Research, 75, 38-
46.
Stenfelt, S. (1999). Hearing by bone conduction: Physical and physiological
aspects. Unpublished Thesis No. 1469, Chalmers University of
Technology, Goteborg, Sweden.
Stenfelt, S. (2005). Bilateral fitting of BAHAs and BAHA fitted in unilateral deaf
persons: Acoustical aspects. International Journal of Audiology, 44(3),
178-189.
175
Stenfelt, S., & Goode, R. L. (2005). Bone-conducted sound: Physiological and
clinical aspects. Otology & Neurotology, 26(6), 1245-1261.
Stenfelt, S., Hakansson, B., Jonsson, R., & Granstrom, G. (2000). A bone-
anchored hearing aid for patients with pure sensorineural hearing
impairment: A pilot study. Scandinavian Audiology, 29(3), 175-185.
Taylor, B. (2007). Predicting real world hearing aid benefit with speech
audiometry: An evidence-based review. Retrieved July 05, 2007, from
http://www.audiologyonline.com/Articles/article_detail.asp?article_id=180
2
Thibodeau, L. (2000). Speech audiometry in audiology diagnosis. In R. J.
Roeser, M. Valente & H. Hosford-Dunn (Eds.), Audiology Diagnosis (pp
281-310). New York:Thieme Medical Publishers, Inc.
Thornton, A. R., & Raffin, M. J. M. (1978). Speech-discrimination scores
modeled as a binomial variable. Journal of Speech and Hearing
Research, 21(3), 507-518.
Tjellstrom, A. (2008). Non-auditory considerations in the selection of paediatric
candidates for the baha system. Implantable Hearing Solutions, 2, 65-67.
Tjellstrom, A., & Hakansson, B. (1995). The bone-anchored hearing aid: Design
principles, indications and long-term clinical results. Otolaryngologic
Clinics of North America, 28, 53-57.
Tjellstrom, A., Hakansson, B., & Granstrom, G. (2001). Bone-anchored hearing
aids: Current status in adults and children. Otolaryngologic Clinics of
North America, 34, 337-364.
Tringali, S., Grayleli, A. B., Bouccara, D., Sterkers, O., Chardon, S., Martin, C.,
et al. (2008). A survey of satisfaction and use among patients fitted with
176
a baha. European Archives of Oto - Rhino - Laryngology, 265(12), 1461-
1464.
Troost, B. T., & Walker, M. A. (1998a). Diagnostic principals in neuro-otology:
The auditory system. In R. N. Rosenberg & D. E. Pleasure (Eds.),
Comprehensive neurology (2nd ed., pp. 611-623). New York: Willey &
Sons Inc.
Troost, B. T., & Walker, M. A. (1998b). Figure 15: Representative impedance
measures by tympanogram [image]. Retrieved February 12, 2009, from
htttp://ivertigo.net/vertigo/verhearing.html
Unitron Hearing Ltd. (2007). WiFi Mic: Digital wireless CROS/BiCROS system.
1/04-007 028-5118-02 [image]. Retrieved January 21, 2009, from
http://www.unitron.com/wifimic-prof-brochure.pdf
Valente, M. (1996). Hearing aids: Standards, options and limitations. New York:
Thieme Medical Publishers Inc.
Valente, M., Valente, M., & Mispagel, K. (2006). Fitting options for adult patients
with single sided deafness [image]. Retrieved January 21, 2009, from
http://www.audiologyonline.com/articles/pf_article_details.asp?article_id=
1629
Van de Heyning, P., Vermeire, K., Diebl, M., Nopp, P., Anderson, I., & De
Ridder, D. (2008). Incapacitating unilateral tinnitus in single-sided
deafness treated by cochlear implantation. Annals of Otology, Rhinology
& Laryngology, 117(9), 645-652.
Van Leeuwen, J. P., Braspenning, J. C., Meijer, H., & Cremers, C. W. (1996).
Quality of life after acoustic neuroma surgery. Annuals of Otology,
Rhinology & Laryngology, 105, 423-430.
177
Van Wanrooij, M. M., & Van Opstal, A. J. (2004). Contribution of head shadow
and pinna cues to chronic monaural sound localisation. The Journal of
Neuroscience, 24(17), 4163-4171.
Vaneecloo, F. M., Ruzza, I., Hanson, J. N., Gerard, T., Dehaussy, J., Cory, M.,
et al. (2001). The monaural pseudo-stereophonic hearing aid (baha) in
unilateral total deafness: A study of 29 patients. Revue de Laryngologie
Otologie Rhinologie (Bord), 122(5), 343-350.
Vermeire, K., Nobbe, A., Schleich, P., Nopp, P., Voormolen, M. H., & Van de
Heyning, P. (2008). Neural tonotopy in cochlear implants: An evaluation
in unilateral cochlear implant patients with unilateral deafness and
tinnitus. Hearing Research, 245, 98-106.
Vermeire, K., & Van de Heyning, P. (2009). Binaural hearing after cochlear
implantation in subjects with unilateral sensorineural deafness and
tinnitus. Audiology & Neurotology, 14, 163-171.
Versfeld, N. J., Daalder, L., Festen, J. M., & Houtgast, T. (2000). Method for the
selection of sentence materials for efficient measurement of the speech
reception threshold. Journal of the Acoustical Society of America, 107(3),
1671-1684.
Virtual Medical Centre (2007) Anatomy of the ear [image]. Retrieved January
18, 2009, from http://www.virtualmedicalcentre.com/anatomy.asp?sid=29
Wazen, J. J., Spitzer, J. B., Ghossaini, S. N., Fayad, J. N., Niparko, J. K., Cox,
K., et al. (2003). Transcranial contralateral cochlear stimulation in
unilateral deafness. Otolaryngology - Head and Neck Surgery, 129(3),
248-254.
178
Weber, P. C. (2002). Medical and surgical considerations for implantable
hearing prosthetic devices. American Journal of Audiology, 11(2), 134-
138.
Weber, P. C., Roush, J., & McElveen, J. T. (1992). Application of an implantable
bone conduction hearing device to patients with unilateral sensorineural
hearing loss. Laryngoscope, 102(5), 538-542.
Welsh, L. W., Welsh, J. J., Rosen, L. F., & Dragonette, J. E. (2004). Functional
impairments due to unilateral deafness. Annals of Otology, Rhinology &
Laryngology, 113, 987-993.
Wikipedia contributors. (2009a). Otitis externa. Retrieved January 23, 2009,
from http://en.wikipedia.org/wiki/Otitis_externa
Wikipedia contributors. (2009b). Otoacoustic emissions. Retrived January 17,
2009, from http://en.wikipedia.org/wiki/Otoacoustic_emissions
Wilson, D., Walsh, P., Sanchez, L., & Read, P. (1998). Hearing impairment in
an Australian population. Adelaide, Australia: Centre for Population
Studies in Epidemiology & South Australian Department of Human
Services.
World Health Organisation. (2006). Deafness and hearing impairment fact sheet
number 300 [Electronic version]. Genevea, Switzerland: Author.
Zemlin, W. R. (1988). Speech and hearing science: Anatomy and physiology
(3rd ed.). Englewood Cliffs, New Jersey: Prentice Hall.
179
Chapter 10: Appendices
180
Appendix I
Technical specifications of Compact and Divino sound processor models
Compact Divino Specifications Measurements at full gain
Size (lxwxh) 30x17x10mm 27x20x11mm Weight 11g (including battery) 11g (including battery) Colours Black, beige, grey Black, blonde, silver grey, brown
Compression ACGo Automatic gain control output compression ACGo Automatic gain control compression Frequency control Low frequency trim pot Low frequency trim pot
Battery voltage 1.1-1.5V 1.1-1.5V Current consumption 0.7mA (in silence) 0.9mA (at 60dB SPL, at 1600Hz) 1.2mA (in silence) 1.6mA at 60dBSPL
Frequency range 250-7000Hz 250-7000Hz Peak OFL at 90dB SPL 110dB rel. 1 micro N 120dB rel. 1uN Peak OFL at 60dB SPL 103dB rel. 1 micro N 103dB rel 1uN
Harmonic distortion THD 60 Below 3% above 600Hz Below 3% at 600Hz Equivalent input noise 26dB SPL 26dB SPL
Battery type 13 13 Electrical input sensitivity (1mVRMS) 98dB rel. 1 micro N, 1600Hz 100dB rel 1uN, 1600Hz
Electrical input equivalent at an acoustic input of 70dB SPL 1.5mV, 1600Hz 1mV, 1600Hz Input impedance 3Kohms >3Kohms
Compression attack time 40ms 8ms Compression release time 80ms 500ms
Compression ratio 8:01 Infinity:1
Technical specifications of Compact and Divino adapted from Audiology Manual, Entific Medical Systems (2003) and Divino Data Sheet, Cochlear Limited (2005).
181
APPENDIX II
Revised AB words lists
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
List 1 List 2 List 3 List 4 List 5 List 6 List 7 List 8
Fan Fun Thug Hush Jug Bath Have Hug
Rug Will Witch Gas Latch Hum Wig Dish
Ship Vat Teak Thin Wick Dig Buff Ban
Cheek Shape Wrap Fake Faith Five Mice Rage
Haze Wreath Vice Chime Sign Ways Teeth Chief
Dice Hide Jail Weave Beep Reach Jays Pies
Both Guess Hen Jet Hem Joke Poach Wet
Well Comb Shows Rob Rod Noose Rule Cove
Jot Choose Food Dope Vote Pot Den Loose
Move Job Bomb Lose Shoes Shell Shock Moth
% correct % correct % correct % correct % correct % correct % correct % correct
182
APPENDIX II continued
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Condition Test rod BAHA Unaided
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
Presentation level __dBHL
List 9 List 10 List 11 List 12 List 13 List 14 List 15 Math Wish Badge Fish Fib Fill Kiss
Hip Dutch Hutch Duck Thatch Catch Buzz
Gun Jam Kill Path Sum Thumb Hash
Ride Heath Thighs Cheese Heel Heap Thieve
Seige Laze Wave Race Wide Wise Gate
Veil Bike Reap Hive Rake Rave Wife
Chose Rove Foam Bone Goes Got Pole
Shot Pet Goose Wedge Shop Shown Wretch
Web Fog Not Log Vet Bed Dodge
Cough Soon Shed Tomb June Juice Moon
% correct % correct % correct % correct % correct % correct % correct
183
APPENDIX III
184
Appendix IV
Abbreviated Profile of Hearing Aid Benefit (APHAB)
Patient Number:____________________ Date:_______________
Clinic:___________________________ Signature:________________
Monitoring (non-implanted) Post-operative with BAHA device
3 months 6 months
9 months 12 months
18 months 2 years
Please choose the answer that comes closest to your everyday experience.
Note that each choice includes a percentage. The percentage can be used to
help you decide on the answer. For example, if the statement is true about
75% of the time for you, the answer selected would be “generally”. If you
have not experienced a particular situation, then you should imagine how you
would respond if you were in a similar situation. If you are still not sure how
to respond to that particular situation, leave that item blank.
Always 99% Almost always 87% Generally 75%
Half-the-time 50% Occasionally 25% Seldom 12% Never 1%
Always Almost Always
Generally Half-the-time
Occasionally Seldom Never
1. When I am in a crowded grocery shop talking to the assistant, I can follow the conversation.
2. I miss a lot of information when I'm listening to a lecture or a church sermon.
3. Unexpected sounds, like a smoke detector or alarm bell are uncomfortable.
4. I have difficulty hearing a conversation when I'm with one of my family at home.
5. I have trouble understanding the speakers in a movie or theatre.
185
Appendix IV continued
Abbreviated Profile of Hearing Aid Benefit (APHAB) Page 2 6. When I am listening to the news on the car radio, and family members are talking, I have trouble hearing the news.
7. When I am at the dinner table with several people and am trying to have a conversation with one person, understanding the speech is difficult.
8. Traffic noises are too loud.
9. When I am talking with someone across a large empty room, I understand the words.
10. When I am in a small room, being interviewed or asked questions, I have difficulty following the conversation.
11. When I am at the theatre watching a film or play, and the people around me are whispering or rustling sweet papers, I can still make out the dialogue.
12. When I am having a quiet conversation with a friend, I have difficulty understanding.
13. The sound of running water, such as the toilet or shower is uncomfortably loud.
14. When a speaker is addressing a small group, and everyone is listening quietly, I have to strain to understand.
15. When I'm in a quiet conversation with my doctor in an examination room, it is hard to follow the conversation.
16. I can understand conversations even when several people are talking.
186
Appendix IV continued
Abbreviated Profile of Hearing Aid Benefit (APHAB) Page 3 17. The sounds of building work or road repairs are uncomfortably loud.
18. It's hard for me to understand what is being said at least at lectures or church services.
19. I can communicate with others when we are in a crowd.
20. The sound of a fire engine siren close by is so loud that I need to cover my ears.
21. I can follow the words of a sermon when listening to a religious service.
22. The sound of screeching tyres is uncomfortably loud.
23. I have to ask people to repeat themselves in one to one conversations in a quiet room.
24. I have trouble understanding others when an air conditioner or fan is on.
COMMENTS/NOTES_______________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
187
Appendix V
Glasgow Hearing Aid Benefit Profile (GHABP)
Part 1- Prior to BAHA fitting
Patient name:______________________ Date:____________________
Clinic:___________________________ Signature:________________
This form is to be filled in by the patient prior to BAHA fitting. Please tick the relevant box for each question below. Only one tick at each question is allowed. 1. Listening to the television with other family or friends when the
volume is adjusted to suit other people. Does this situation happen in your life? Yes No
How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
2. Having a conversation with one other person when there is no background noise. Does this situation happen in your life? Yes No
How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
3. Carrying on a conversation in a busy street or shop.
Does this situation happen in your life? Yes No
How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
188
Appendix V continued
Glasgow Hearing Aid Benefit Profile (GHABP)
Part 1- Prior to BAHA fitting
Patient name:______________________ Date:____________________
Clinic:___________________________ Signature:________________
4. Having a conversation with several people in a group.
Does this situation happen in your life? Yes No
How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
We have dealt with some of the situations which in our experience can lead to difficulty in hearing. What we would like you to do is to nominate up to four new situations in which it is important for you as an individual to be able to hear as well as possible. 5._______________________________________________________________ __________________________________________________________________________________________________________________________________ How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
6._______________________________________________________________ __________________________________________________________________________________________________________________________________ How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
189
Appendix V continued
Glasgow Hearing Aid Benefit Profile (GHABP)
Part 1- Prior to BAHA fitting
Patient Number:______________________ Date:_________________
Clinic:___________________________ Signature:________________ 7.__________________________________________________________________________________________________________________________________________________________________________________________________ How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
8._______________________________________________________________ __________________________________________________________________________________________________________________________________ How much difficulty do you have in this situation?
How much does any difficulty in this situation worry, annoy or upset you?
0 N/A 0 N/A 1 No difficulty 1 Not at all 2 Only slight difficulty 2 Only a little 3 Moderate difficulty 3 A moderate amount 4 Great difficulty 4 Quite a lot 5 Can not manage at all 5 Very much indeed
190
APPENDIX VI
Glasgow Hearing Aid Benefit Profile (GHABP)
Part 2 - After initial assessment or BAHA fitting
Patient Number:_____________________ Date:__________________
Clinic:___________________________ Signature:_______________ Monitoring (non-implanted) Post-operative with BAHA device
3 months 6 months
9 months 12 months
18 months 2 years
Please tick the relevant box for each question below. Only one tick at each question is allowed. 1. Listening to the television with other family or friends when the volume is adjusted to suit other people.
Does this situation happen in your life? 1 Yes 0 No
In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
2. Having a conversation with one other person when there is no background noise.
Does this situation happen in your life? 1 Yes 0 No
In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
191
APPENDIX VI continued
Glasgow Hearing Aid Benefit Profile (GHABP) Part 2: After initial assessment or BAHA fitting 3. Carrying on a conversation in a busy street or shop.
Does this situation happen in your life? 1 Yes 0 No
In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
4. Having a conversation with several people in a group.
Does this situation happen in your life? 1 Yes 0 No
In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
When you filled in the Glasgow Questionnaire Part 1 you came up with some situations in which it is important for you as an individual to be able to hear as well as possible. We would now like you to use the same situations as in Part 1 and answer the following questions. 5.________________________________________________________________________________________________________________________________________________________________________________________________________________________________ In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
192
APPENDIX VI continued
Glasgow Hearing Aid Benefit Profile (GHABP) Part 2: After initial assessment or BAHA fitting 6.___________________________________________________________________________________________________________________________________________________________________________________________________________________________________ In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
7.___________________________________________________________________________________________________________________________________________________________________________________________________________________________________In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
8.___________________________________________________________________________________________________________________________________________________________________________________________________________________________________ In this situation, what proportion of your time do you wear your hearing aid?
In this situation, how much does your hearing aid help you?
In this situation, with your hearing aid, how much difficulty do you now have?
For this situation, how satisfied are you with your hearing aid?
0 N/A 0 N/A 0 N/A 0 N/A 1 Never/Not at all 1 H.aid is no use at all 1 No difficulty 1 Not satisfied at all 2 About 1/4 of the time 2 H.aid is some help 2 Only slight difficulty 2 A little satisfied 3 About 1/2 of the time 3 H.aid is quite helpful 3 Moderate difficulty 3 Reasonably satisfied 4 About 3/4 of the time 4 H.aid is a great help 4 Great difficulty 4 Very satisfied 5 All the time 5 Hearing is perfect
with aid 5 Can not manage at all
5 Delighted with aid
193
APPENDIX VII
Single Sided Deafness Questionnaire (SSDQ)
Patient Number:________________________ Date:_______________
Clinic:___________________________ Signature:________________
Appointment:
Monitoring (non-implanted) Post-operative with BAHA device
3 months 6 months
9 months 12 months
18 months 2 years
1. How many days per week 5. How do you assess the value of your do you use your device? new device in the following situations
Every day (7 days) compared to your previous situation Most days (5-6 days) (unaided)? Occasionally (3-4 days) Sometimes (1-2 days) 5.1 Talking to one person in a quiet Not at all situation.
Better 2. How many hours per day do you use Worse your device? No difference
More than 8 hours 4-8 hours 5.2 Talking to one person among a 2-4 hours group of people. Less than 2 hours Better
Worse 3. Has your quality of life improved due No difference to the device?
Yes 5.3 Listening to music. No Better Both yes and no Worse No difference No difference
4. Try to determine your satisfaction 5.4 Listening to TV/Radio. or dissatisfaction with the device. Better Tick the relevant box on a 10 point Worse scale. No difference
10 Very satisfied 9 5.5 At a dinner table, talking to the 8 person sitting on your deaf side 7 Better 6 Worse 5 No difference No difference 4 3 2 1
194
APPENDIX VII continued
Single Sided Deafness Questionnaire (SSDQ)
Patient Number:________________________ Date:_______________
Clinic:___________________________ Signature:________________
Appointment:
Monitoring (non-implanted) Post-operative with BAHA device
3 months 6 months
9 months 12 months
18 months 2 years
6. Do you find it easier to locate 8. How do you find the handling of the where a sound is coming from compared to your previous situation
device?
(unaided)? Very easy Easy
Yes Acceptable No Difficult Both yes and no Very difficult No difference
7. How satisfied are you with the aesthetics and cosmetics of the device?
10 Very satisfied 9 8 7 6 5 Acceptable 4 3 2 1 Unsatisfied
9. Please write down other comments you might have about the device.
_______________________________________________________
195
APPENDIX VIII
Ground Floor E-Block
Sir Charles Gairdner Hospital
Hospital Avenue, Nedlands
Western Australia 6009
Tel: 61 8 9346 3555
Fax: 61 8 9346 3637
www.lehi.com.au
Patient Information Rehabilitation of unilateral profound sensorineural
hearing loss with a bone anchored hearing aid
Introduction You are being invited to take part in a research study. Before you make your decision to participate, it is important for you to understand why the research is being done and what it would involve. Please take as much time as you need to read the following information carefully and discuss it with friends, relatives and your doctor if you wish. Ask us if there is anything that is not clear or if you would like more information. What is the purpose of the study? The purpose of this study is to measure the performance of the Bone Anchored Hearing Aid (BAHA). You are invited to participate because you have been considered as a candidate for a BAHA. Although the device has been in use for many years, some patients are reporting some improvements that have not been noted before. These relate to the ability to judge the direction of sound and hearing in the presence of background noise. We are undertaking this study to measure these. The study will also measure the Quality of Life (QOL) and how this changes after the implantation of the BAHA. What will happen during the test? If you participate in the study, you will undergo testing at different stages; at your initial assessment, and if you decide to proceed with the surgery, post-operatively. You will be asked to undertake a number of tests, some which measure your hearing in different situations, and others in the form of a survey. The hearing tests include a standard audiometry hearing test, a speech test, and a sound localisation test. Sounds are heard from speakers, and you will be asked to respond by pressing a button or verbally. In some cases your device will be switched off. These tests will take approximately 30 to 45 minutes. The QOL survey is in three parts, and requires about 30 minutes to complete; this can be done at home. Testing will be performed before surgery, and at 3, 6 12, and 18 months after surgery. All of these tests are standard, and each patient would undertake them a number of times before and after implantation. However, in this study we will undertake more of these tests in one session, and conduct them more regularly. Do I have to take part? Participation in the study is completely voluntary. Any decision to participate may be withdrawn at any time for whatever reason by reporting to your clinic in writing. Withdrawal or non-participation can be done without prejudice. It will in on way affect the care you receive as a patient at your clinic. If you do decide to participate you will be asked to sign a consent form indicating your willingness and informed participation
196
in this experiment. You will be given this information sheet for your records and a copy of your signed consent form. What are the possible risks from participation? All of the tests are standard in an audiology clinic, and there are no risks associated with them.
What happens to the results and records? Trial records will be kept confidentially by the Lions Ear and Hearing Institute for five years from the completion of the experiment and may be destroyed at any time thereafter. Identifying information may be viewed by the experimental team; otherwise your records will remain strictly confidential. Personal data will not leave the experimental database in a form that allows you to be identified. The results of this research will be made available through conferences or professional journals. By taking part in this study, you agree not to restrict the use of data that has been collected. Your rights under any applicable data protection laws are not affected.
Are there any study costs and reimbursements? There are no extra costs for you to be involved in this study. There are no reimbursements for participating.
What are the possible benefits of taking part? The information obtained during this study will be important in measuring how well the BAHA works for people with single sided hearing loss. The information you provide will enable us to be better informed of the progress of your rehabilitation, and any problems or concerns you may have. This information will be invaluable for ear specialists and audiologists when assessing the suitability of patients for a BAHA, and when counselling candidates for a BAHA about the probable advantages and benefits of the implant. This study will therefore be very useful for all future BAHA patients.
Funding of the study This study is funded by the Lions Ear and Hearing Institute. Ethical Approval of the Study This study will be carried out in a manner conforming to the principles set out by the "National Statement on Ethical Conduct in Research involving Humans" and according to the Good Clinical Practice Guidelines and the International Conference of Harmonisation. Consideration has been given to the welfare, rights, beliefs, perceptions, customs and cultural heritage, both individual and collective, of the persons involved in the research. Previous research carried out elsewhere: This research has not been conducted previously. Further information, and contacts during the study If you have any questions or concerns now or at any time about the study, your safety or your rights, please ask any of the investigators. Their numbers are listed below. Investigators: Ms Katrise Eager Phone: 61 8 9346 3555
Professor Marcus Atlas Phone: 61 8 9346 3633 Dr Robert Eikelboom Phone: 61 8 9346 3735
197
APPENDIX IX Ground Floor E-Block
Sir Charles Gairdner Hospital
Hospital Avenue, Nedlands
Western Australia 6009
Tel: 61 8 9346 3555
Fax: 61 8 9346 3637
www.lehi.com.au
PATIENT CONSENT FORM FOR PARTICIPATON IN CLINICAL STUDY
Title of Project: Rehabilitation of unilateral profound sensorineural hearing loss with a bone anchored hearing aid. Investigators: Katrise Eager, Professor Marcus Atlas, Dr Robert Eikelboom Subject Name: ___________________________ Date of Birth ________________ I have been given clear information (verbal and written) about this study and have been given time to consider whether I wanted to take part. I have been told about the possible advantages and risks of taking part in this study and I understand what I am being asked to do. I have been able to ask questions and all questions have been answered satisfactorily. I know that I do not have to take part in the study and that I can withdraw at any time during the study without affecting my future medical care. My participation in the study does not affect any right to compensation that I may have under statute or common law. I agree to take part in this research study and for the data obtained to be published, provided my name or other identifying information is not used. ____________________________________________________________________ Name of Patient Signature of Patient Date
____________________________________________________________________ Name of Witness to Patient Signature Signature of Witness to Signature Date
____________________________________________________________________ Name of Investigator Signature of Investigator Date
The Sir Charles Gairdner Hospital Human Research Ethics Committee has given ethics approval for the conduct of this project. If you have any ethical concerns regarding the study you can contact the secretary of the Sir Charles Gairdner Hospital Human Research Ethics Committee on telephone no. (08) 9346 2999. All study participants will be provided with a copy of the Information Sheet and Consent Form for their personal records. If you are unclear about anything you have read in the Patient Information Sheet or this Consent Form, please speak to your doctor before you sign this Consent Form.
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APPENDIX X
Revised BKB/A Sentences Sentence List 1 Date:______________ Subject Code:_____________ Tester:_______________ Clinic: LEHI SYD Appt: Pre-Op 1 month 3months 6 months 9 months 12 months 18 months 2 years Condition: Test band Aided (own BAHA) Unaided SNR: +11dB +9dB +7dB +5dB +3dB + 1dB -1dB -3dB -5dB -7dB -9dB -11dB The clown had a funny face. _______
The car engine’s running. _______
She cut with her knife. _______
Children like strawberries. _______
The house had nine rooms. _______
They’re buying some bread. _______
The green tomatoes are small. _______
He played with his train. _______
The postman shut the gate. _______
They’re looking at the clock. _______
The bag bumps on the ground. _______
The boy did a handstand. _______
A cat sits on the bed. _______
The truck carried fruit. _______
The rain came down. _______
The ice cream was pink. _______
TOTAL SCORE (LKW) =_______ x 2 = _______%
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APPENDIX XI
CLINICAL DATA FORM
Title of Project: Rehabilitation of unilateral profound sensorineural hearing loss with a bone anchored hearing aid Clinic:_____________________________________________________________ Primary audiologist: ___________________________________________________ Patient Name:________________________________________________________ Date of Birth: __________________________________ Diagnosis of single sided deafness
Acoustic Neuroma NFII patient Other (please specify) ___________________________________________
Surgery Surgeon’s name:______________________________
Translabyrinthine Middle fossa Other (please specify)_________________________________________
Affected side
Left Right
Previous trial of hearing aids Time period of trial
Transcranial 1 month CROS wireless - BTE 3 months or less CROS wired – BTE 6 months or less CIC 12 months or less Traditional bone conductor 12 months+ Never Other (please specify)____________________________
Period of profound sensorineural hearing loss in affected ear (confirmed audiologically as best as possible)
3 months or less 6 months or less 12 months or less 2 years or less 2-5 years 5-10 years 10+ years
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APPENDIX XII
HEARING AID STATUS
Questionnaire
Date
1. Are you currently in the workforce Yes No
2. Are you wearing any hearing device? Yes No
If you answered No, there are no further questions. Otherwise please answer question 3.
3. What device are you wearing? Please tick one or more, and indicate the device brand and
model if known in the space provided.
a. Contralateral routing of the signal (CROS) aid,
consisting of two parts with a cord that runs along your
hair-line.
Yes No
Brand/Model:
b. Bilateral contralateral routing of the signal (BiCROS) –
with two hearing aids with a cord that runs along your
hair-line.
Yes No
Brand/Model:
c. Frequency modulated (FM) system, such as Phonic
Ear FM system or an EduLink system. Yes No
Brand/Model:
d. Conventional air conduction hearing aid in your better
ear. Yes No
Which Type? Completely in the canal (CIC)
In the canal (ITC)
In the ear (ITE)
Behind the ear (BTE)
Brand/Model:
e. Other Yes No
Brand/Model:
Thank you for taking the time to complete this survey.
