PFT Interpretation and Reference Values
Transcript of PFT Interpretation and Reference Values
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PFT Interpretation and
Reference Values
September 21, 2018
Eric Wong
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Objectives
• Understand the components of PFT
• Interpretation of PFT
• Clinical Patterns
• How to choose Reference Values
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3 Components
• Spirometry
• Lung Volumes
• Diffusing Capacity
• Flow
• Capacity
• Gas Exchange
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Distribution of TLC by
population:
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PFT Interpretation
(Pellegrino et al., 2005)
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Spirometry
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FLOW-VOLUME LOOP
Flo
w
I
E
Volume
TLC
FRC RV
Tidal Breathing
Peak Flow
Time
Volume
VOLUME-TIME CURVE
RV
TLC
0 1 2 3 4 5
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Forced Expired Flow
Definitions:
• PEF – Peak expiratory flow
• FVC – forced vital capacity
• FEV1 – Forced expiratory volume in 1 sec
• FEF25-75% - Mean forced expiratory flow between 25%
and 75% of FVC
• FEF75% - Forced expiratory flow at 75% FVC
Flo
w
I
E
Volume
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Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH SMALL AIRWAY OBSTRUCTION
Pst
Palv
Palv
Pst
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Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH EMPHYSEMA & AIRWAY OBSTRUCTION
Pst
Palv
Palv
Pst
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Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH A FIXED EXTRATHORACIC OBSTRUCTION
Pst
Palv
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Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH A VARIABLE EXTRATHORACIC OBSTRUCTION
Floppy
Segment
Forced Inspiration = (-)Forced Expiration = (+)
P = 0
Pst
Palv
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Flow
I
E
Volume
AIRWAY REVERSIBILITY
Criteria for Reversibility:
> 12% and 200ml change in
FEV1 or FVC
Pre test Medication?
• If test is to determine reversibility – No short-acting beta agonist within
4hrs, no long-acting within 12hr prior
• If test is to determine whether patient’s lung function is improving w/
therapy, then patient can continue use of medication prior
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LUNG VOLUMES
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MEASURING LUNG VOLUMES
Gas dilution:
1. Nitrogen washout
2. Helium dilution
Body plethysmographyRV
ERV
VT
IRV
FRC
VCIC
TLC
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Trapped AirVentilated Lung
Dilution methods measure only the ventilated lung
volume, but the Body box method measures all gas in
the lungs (trapped air + ventilated lung)
C1V1 = C2V2
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THE LUNG VOLUME PATTERNS SEEN WITH
INCREASING AIRWAY OBSTRUCTION
TLC
FRCRV
ERV
VC
Normal
Normal FRC
Normal RV
Zero Volume
Normal TLC
Slight
ModerateSevere
Very Severe
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DIFFUSING CAPACITY
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DIFFUSING CAPACITY
Carbon monoxide is used to measure diffusing capacity
because CO is usually not present in the blood and CO
is diffusion-limited.
DLCO =VCO.
PACO - PcCO
PcCO is usually 0, therefore: DLCO =
VCO.
PACO
VCO.
PACO
PcCOThe units are: ml/min VCO for
each mm Hg difference between
PACO and PcCO.
.
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Diffusing capacity is dependent on:
DLCO ≈ (VA)(Pulmonary Cap Blood Volume)([Hb])
(Alveolar-capillary membrane thickness)([COHb])
DLCO/VA seems to be a way to eliminate the effects of VA but
this is not a perfect correction.
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DLCO/VA overcorrects
when VA is low
EFFECTS OF LUNG VOLUME ON DLCO and DLCO/VA
0 25 50 75 100 125 1500
100
200
300
400
DLCO
DLCO/V A
Alveolar Volume (% Predicted TLC)
DLC
O (
% v
alu
e a
t n
orm
al
TL
C)
DLC
O/V
A(%
valu
e a
t n
orm
al
TL
C)
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PFT – Diffusion Capacity
• Pure airway disease – asthma, chronic
bronchitis – normal
• Restrictive Disease with normal lung
parenchyma and pulmonary vasculature
– Neuromuscular disease, obesity
– Low DLCO
– DLCO / VA – normal to high
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PFT – Diffusion Capacity
• Low – DLCO
– Alveolar disease – emphysema, alveolitis, pulm edema
– Thickened Interstitium – Pulm fibrosis
– Pulmonary vascular disease – Pulm hypertension
– Anemia
– High carboxyhemoglobin – just after smoking, CO poisoning
– Low cardiac output – cardiogenic shock
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DLCO
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PFT Interpretation
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PFT Interpretation
(Pellegrino et al., 2005)
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Spirometry
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INTERPRETING PFTs
Is FVC normal?
>LLN
Is there evidence for airway obstruction?
FEV1/VC < LLN
- more sensitive than FEV1/FVC to detect obstruction
- FVC more dependent on flow
- take largest of VC, FVC, Slow VC, Insp VC
Is there any change after bronchodilator?
FEV1 or FVC >12% and 200 ml
(Adapted from Pellegrino et al., 2005)
Spirometry
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Global Strategy for Diagnosis, Management and Prevention of COPD
Classification of Severity of Airflow Limitation in COPD*
In patients with FEV1/FVC < 0.70:
GOLD 1: Mild FEV1 > 80% predicted
GOLD 2: Moderate 50% < FEV1 < 80% predicted
GOLD 3: Severe 30% < FEV1 < 50% predicted
GOLD 4: Very Severe FEV1 < 30% predicted
*Based on Post-Bronchodilator FEV1
© 2015 Global Initiative for Chronic Obstructive Lung Disease
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For obstruction FEV1/VC previously determined to be
<LLN
Classification of Severity
(Pellegrino et al., 2005)
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Lung Volumes
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Lung Volumes
Is there evidence for a restrictive defect?
TLC < LLN
Are the lungs hyperinflated?
TLC > ULN
Is there a high RV or FRC?
RV or FRC > ULN
Is there evidence for air trapping?
RV / TLC > ULN
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Diffusing Capacity
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Diffusing Capacity
Are DLCO or DLCO / VA decreased?
< LLN
Are DLCO or DLCO / VA increased?
> ULN
(Pellegrino et al., 2005)
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Patterns
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THE LUNG VOLUME PATTERNS SEEN WITH
INCREASING AIRWAY OBSTRUCTION
TLC
FRCRV
ERV
VC
Normal
Normal FRC
Normal RV
Zero Volume
Normal TLC
Slight
ModerateSevere
Very Severe
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LUNG VOLUME PATTERNS SEEN IN PATIENTS
WITH AIRWAY OBSTRUCTION
Degree of
Obstruction TLC VC FRC RV/TLC RV
N N N N N
N N
N N
N N
Slight
Moderate
Severe
Very Severe
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LUNG VOLUME PATTERNS SEEN IN PATIENTS
WITH RESTRICTIVE DISEASE
Causes of
Restriction TLC VC FRC RV/TLC RV
Obesity
Chest wall mechanics
Parenchyma
Pleural space disease
Weak chest muscles
N N N N
N N
N N
N N
N
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TYPICAL LUNG FUNCTION PATTERNS
AbnormalityFEV1
FVC VC TLC RV
RV
TLC FRC DLCO
Asthma N N N
Emphysema N
Chronic Bronchitis N N
Chest wall or Obesity N N N N N N
Pulmonary Fibrosis N N N
Muscle Weakness N N N
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PFT Interpretation
(Pellegrino et al., 2005)
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PFT Interpretation Algorithm
• Legend
– PV – pulmonary vascular
– CW – chest wall
– NM – neuromuscular
– ILD – interstitial lung diseases
– CB – chronic bronchitis
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Reference Values
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Ideal Reference Values
• Find healthy people and do PFT on
them
• Based on the results, develop equations
• Test equations on other normal and
patients with diseases
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Realistic Approach
• Find reference set best fit to your
population
• Adopt their standard deviation if your
population has similar distribution
• Use one equation if possible to fit full
age range
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Global Lung Function Initiative
• From European Respiratory Societ
• Clinical Research Group
• Submission of lung function results from
> 70 groups
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GLI
• 2012 – Spirometry reference set
• 2017 – DLCO reference set
• ? – Lung Volumes reference set
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Reference Sets
Canadian Thoracic Society
• Spirometry
– GLI
– NHANES
– Gutierrez / Peds
• Lung volumes & DLCO
– GLI
– Gutierrez / Peds
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Summary
ATS approach to PFT interpretation
Poor quality test can lead to misdiagnosis
Reference Values – awaiting GLI