Pulmonary Function Robert C. Strunk, MD Strominger Professor of Pediatrics Washington University...
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Transcript of Pulmonary Function Robert C. Strunk, MD Strominger Professor of Pediatrics Washington University...
Pulmonary Function
Robert C. Strunk, MDStrominger Professor of Pediatrics
Washington University School of Medicine
St. Louis Children’s Hospital
Division of Allergy, Immunology, and
Pulmonary Medicine
Disclosures
Employment Washington University School of Medicine
Research Interests NHLBI
Financial Interests None
Chair, Pediatric Adjudication Committee, GSK study of safety and benefit of FP/salmeterol vs. FP
Spirometry
For now, spirometry is best test to: • Monitor asthma status• Look for evidence of asthma• Look for evidence of other diagnoses
Volume-Time Plot
Forced Vital Capacity Maneuver
Airflow, L/sec
Lung volume
Definitions
FVC – Forced Vital Capacity
Volume of air exhaled after a maximal inspiration to total lung capacity. This volume is expressed in Liters
FEV1 – Forced Expiratory Volume in 1 second
Volume of air exhaled in the first second of expiration.
This volume is expressed in Liters
FEF 25-75%
Mean expiratory flow during the middle half of the FVC maneuver; reflects flow through later emptying airways, not necessarily the small airways
FEV1/FVC – Ratio (%)
Volume of air expired in the first second, expressed as a percent of FVC
Performance of FVC maneuver
Patient assumes the position (typically standing)• Puts nose clip on• Inhales maximally• Puts mouthpiece in mouth and closes lips around mouthpiece
(open circuit)• Exhales as hard and fast and long as possible• Repeat instructions if necessary – effective coaching is essential• Give simple instructions• Repeat minimum of three times (check for repeatability)
Special Considerations in Pediatric Patients
Ability to perform spirometry dependent on developmental age of child, personality, and interest.
Patients need a calm, relaxed environment and good coaching. Patience is key.
Be creativeUse incentivesEven with the best of environments and coaching, a
child may not be able to perform spirometry.
ATS Acceptable CriteriaWithin Maneuver
Free from artifacts, such as• Cough during the first second of exhalation• Glottis closure that influences the measurement• Early termination or cut-off• Effort that is not maximal throughout• Leak• Obstructed mouthpiece
Good starts• Extrapolated volume < 5% of FVC or 0.15 L, whichever is greater
Satisfactory exhalation• Duration of ≥ 6 s (3 s for children < 10) or a plateau in the volume–
time curve or• If the subject cannot or should not continue to exhale
ATS Acceptable CriteriaWithin Maneuver
After three acceptable spirograms have been obtained, apply the following tests• The two largest values of FVC must be within 0.150 L of each other• The two largest values of FEV1 must be within 0.150 L of each other
If both of these criteria are met, the test session may be concluded
If both of these criteria are not met, continue testing until• Both of the criteria are met with analysis of additional acceptable
spirograms or
• A total of eight tests have been performed (optional) or• The patient/subject cannot or should not continue
Save, as a minimum, the three satisfactory maneuvers
Spirometry Interpretation: So what constitutes normal?
Normal values vary and depend on:• Height • Age • Gender• Ethnicity
Spirometry Interpretation: Obstructive vs. Restrictive
Defect Obstructive Disorders• Characterized by a limitation of
expiratory airflow so that airways cannot empty as rapidly compared to normal (such as through narrowed airways from bronchospasm, inflammation, etc.)
Examples:• Asthma• Emphysema• Cystic Fibrosis
Restrictive Disorders• Characterized by reduced lung
volumes/decreased lung compliance
Examples:• Interstitial Fibrosis• Scoliosis• Obesity• Lung Resection• Neuromuscular diseases• Cystic Fibrosis
Spirometry Interpretation: Obstructive vs. Restrictive
Defect Obstructive Disorders
• FVC nl or↓• FEV1 ↓• FEF25-75% ↓ • FEV1/FVC ↓• TLC nl or ↑
Restrictive Disorders• FVC ↓• FEV1 ↓ • FEF 25-75% nl to ↓• FEV1/FVC nl to ↑• TLC ↓
Severity of any spirometric abnormalities based on the FEV1
Degree of severity FEV1 % predictedMild >70Moderate 60-69Mod severe 50-59Severe 35-49Very Severe < 35
based on ATS/ERS criteria
Criteria Used at Washington University PFT Lab
FEV1 Normal (82-118% predicted)FVC Normal (82-118% predicted)TLC < 80 % predicted for restrictionRV/TLC above 30% for air trapping
Degree of severity FEV1 % predictedMild > 70Moderate 50-70Severe < 50
When you see the tracings below, which of these prompts should you give the
participant Take in a deeper breath Blow out harder
and faster
Try not to cough Blow out longer Good Test
The flow volume loop below is representative of
Extrapolation or time zero error
Clipped inspiratory loop
Obstructive pattern
Restrictive pattern
Glottic closure
When you see the tracings below, which of these prompts should you give the participant
Blow out longer
Good Test
Take in a deeper breath
Try not to cough
Blow out harder and faster
When you see the tracings below, which of these prompts should you give the participant
Take in a deeper breath Blow out harder
and faster
Try not to cough Blow out longer Good Test
The flow volume loop below is representative of
Extrapolation or time zero error
Clipped inspiratory loop
Obstructive pattern
Restrictive pattern
Glottic closure
Back Extrapolation
Exhalation Time During Obstruction
Spirometry-Induced Bronchospasm
Coaching is Key
Bronchodilator Response
Obstruction
Restrictive Pattern
Patient example
Child with inspiratory stridor
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Vocal Cord Dysfunction
Patient example
12 year old boy presents with exercise-induced wheeze for 1 year
Not responsive to bronchodilator used pre-exercise, ICS, OCS
Fixed airway obstruction
Obstruction due to abnormalities of the vocal cords after trauma of intubation and prolonged intubation
Additional history
Automobile accident at age 11 yearsIntubated at scene of accidentComatose for 1 month, followed by complete
neurologic recovery
FEF 25-75%
What is it?What does it measure?Is it a measure of small airways?
FEF 25-75% What is it?
• Mean expiratory flow during middle half of FVC maneuver
What does it measure?• Flow from airways that empty in the middle half of FVC
maneuver
Is it a measure of small airways?• Maybe in normals• In asthma, or obstructive disease, it measures flow from
more obstructed airways which could be small or larger with more obstruction
A problem with FEF: Variability
Dysanapsis
Green, Mead, Turner. Variability of maximum expiratory flow-volume curves. J Appl Physiol 1974 37:67-74• Variability in flows among healthy adults not altered when
flows were corrected for vital capacity• Lung static recoil and bronchomotor tone contributed little
to variability
Concluded that variability in flows between individuals due to differences in airway size independent of lung/parenchyma sizeDifferences may have embryological basis, reflecting
disproportionate but physiologically normal growth within an organ
Dysanapsis
Mead. Dysanapsis in normal lungs assessed by the relationship between maximal flow, static recoil, and vital
capacity. Am Rev Respir Dis 1980 121:339-342
• “There is no association whatsoever between airway diameter and lung size.”
• There are differences between men and women (men 17% larger than women) and between boys and men (boys in late teens similar to girls, suggesting that growth in males occurs late)
Measures Of Dysanapsis
Mead used maximal expiratory flow/static recoil pressure at 50% VC
Weiss and coworkers have used
FEF25-75/FVC as a surrogate
FEF25-75/FVC is correlated with
FEV-1/FVCFEV-1/FVC is the best measure: obtained from
spirometry and normal values available
Dysanapsis Is Affected By Asthma
Weiss et al. Effects of asthma on pulmonary function in children. A longitudinal population-based study. Am Rev Respir Dis 1992 145:58-64.• East Boston cohort of 5-9 year old school children followed
prospectively until age 13 years• Active asthma
• Yes to “Has a doctor ever told you that your child has asthma.”• Wheezing symptoms present in that study year
• Boys with asthma had significantly larger FVC, but normal FEV-1
• Girls with asthma had significantly lower FEV-1, but normal FVC
Compared to children with no history of asthma, after adjusting for previous level of pulmonary function, age, height, and personal and maternal smoking
Clinical Correlates Of Asthma Related To Dysanapsis
Studies of East Boston cohort of school children by Weiss and colleagues
Degree of response to eucapneic hyperventilation: • Correlated with FEF25-75/FVC, but not FEF25-75
• Correlated with FVC (higher levels associated with increased response)
In both studies, response also correlated with current asthma and report of a respiratory illness that led to activity restriction
Case History of dysanapsis
Pulmonary function results at age 7• FVC 157% predicted• FEV-1 115% predicted
Case History
Pulmonary function results at age 7• FVC 157% predicted (82-120%)• FEV-1 115% predicted (82-120%)
Case History
Pulmonary function results at age 7• FVC 157% predicted (82-120%)• FEV-1 115% predicted (82-120%)
• FEV-1/FVC = 65% (> 80%)
Case HistoryPulmonary function results at age 7
• FVC 157% predicted• FEV-1 115% predicted• FEV-1/FVC = 65%
Results obtained 1 month after severe exacerbation requiring intubation and ventilation
1st admission occurred at age 21 monthsIntubation admission was #28, with first
documented hypercarbia with exac at age 4 years
Spirometry History
Age FVC % pred FEV-1 % pred FEV-1/FVC
6 143 126 79
7 157 115 65
8 149 119 72
9 159 129 73
10 127 95 66
11 147 96 58
12 119 91 67
13 100 77 71
14 78 57 68
Conclusions
Spirometry is: • Useful in asthma diagnosis and management• Useful in diagnosis of conditions that can present with
wheezing, or airway noise that can be hard to distinguish from wheezing
• Requires considerable expertise, particularly in children
FEF25-75% does not measure small airways, but instead airways more obstructed that empty later in exhalation