Pulmonary function tests
• Goals
– Don’t memorize! Try to understand…
• What are you measuring and why?
• How are you measuring it?
• What do the results mean? (aka How
to interpret PFTs and impress your
friends)
Pulmonary Function Tests
Practical goals
• Basics about measurements
– What do your measurements reflect
• Two broad categories of disease
– Obstruction (Definition and grading of severity)
– Restriction (Definition, severity, when to suspect
it)
Autoimmune
/Vasculitis
Environmental
/Occupational
Pulmonary
vascular
disease
Inside the mind of a
pulmonologist??
Pneumonia
ARDS
Lung
Cancer
TB and other
Mycobacterial
disease
Sleep
apnea
Obstructive
Lung Diseases
Restrictive
Lung Diseases
Golf, Cubs,
College
basketball
Why measure PFTs?
• Why do any test?
–To look for disease
–To evaluate severity of disease
–To determine response to
treatment
–To prevent disease
What measurements should you
make?
• To know what to lung function to
measure you need to know...
– What does the lung normally do
– How does it do it
– What can cause this to go wrong
What measurements:
Normal lung
• To understand lung
function think in
terms of anatomy
– Airflow
• Gets the gas to the
blood and back again
– Gas exchange
• Lots of air
• Really close to the
capillaries
Normal anatomy
Medium airways….
Small airways….
Alveoli…gas exchange units
Large airways and chest wall
What measurements?
• Airflow (Obstructive diseases)
– How fast (Forced exhaled volume)
• FEV1, and FEV1% (actually FEV1/FVC) and Flow
volume loop (FVL)
• Gas Exchange (Restrictive diseases)
– How much
– Forced Vital Capacity, Total Lung Capacity
(FVC, TLC)
– Diffusion capacity (Diffusion capacity of the
lung for carbon monoxide)
• DLCO
Vt Tidal volume
FRC Functional residual capacity
VC Vital Capacity
RV residual volume
ERV/IRV Expiratory/Inspiratory
reserve volume
TLC Total lung capacity (RV + VC)
These are all measured easily with spirometers
Measuring these requires more
specialized equipment
TLC
TLC
IC
VC
Vt
ERV
RV
RV
FRC
VC
RV
Normal
Vital capacity is reduced in both
obstructive and restrictive diseases
VC
VC
VC
RV
RV
RV
Obstructive
Normal
Restrictive
What are “PFT?s”?
• Spirometry is just the measure of
dynamic lung mechanics
– FEV1 and FVC, and the FEV1/FVC ratio
• Lung volume measurements
– Usually measured as part of “Full PFTs” or
“Complete PFTs”
– Involves more sophisticated (aka expensive)
equipment and technician time
• Diffusion capacity or DLCO
Spirometry
Spirometry requires that you perform a forced expiratory
maneuver (FEM)
How are the measurements made?
Spirometry
Most “PFTs” mean simple spirometry, which is all most patients
need to accomplish the goals of obtaining “PFT’s” in the first place
How are measurements made?
Measuring lung volumes
Some patients also require “Full PFT’s” or lung volume measurements
in addition to spirometry
These are usually the patients in whom restrictive lung disease is
suspected
Gas dilution method of measuring FRC
May underestimate TLC if the patient has emphysema
C1=N/Vbox
C2=N/(Vbox+FRC)
Body plethysmograph
Plethysmography- measures total thoracic gas volume, but is
more cumbersome. Uses Boyle’s law to calculate RV.
Pbox x Vbox= P’box x V’box
Plung
Vlung
Pbox x Vbox
V’box =Vbox+∆V
P’box =Pbox+∆P
Plungx Vlung=P’lungx V’lung
V’lung = Vlung +∆V
P’lung =Plung+∆P
Why measure residual volume?
Look at two people with identical vital capacity
TLC
TLC
Vt
Vt
VC
FRC
RV
FRC
VC
RV
Summary
• What we measure
– Airflow, and gas exchange
• Why we measure it
– Diagnose, follow treatment, prognosticate
• How we measure
• What do you do with the results?
What do the results mean?
(aka How to interpret PFTs and impress your friends)
• Remember the question you want to
answer in the first place
– To look for disease
– To evaluate severity of disease
– To determine response to treatment
– To prevent disease
• For most of these you need a
“normal” value for comparison
What are normal values?
• You don’t have to worry about memorizing
normal values! (woohoo)
– All modern PFT labs have a set of nomograms which they
use to predict normal values
• What you should know
– Normals are derived just like any normal lab
value
– There are limitations to these estimates
• Predicted values are only as good as the
population in which they were measured
• The patient should be from the population
from which the normals are calculated
What do the results mean: Algorhithim for PFT's
Is the FEM adequate?
no
yes
Is the FEV1/FVC
lower than predicted?
yes
This is the definition of
obstruction
Mild
FEV1 >70%
Moderate FEV1 60-70%
Mod severe FEV1 50-60%
Severe
FEV1 <50%
Very severe FEV1 <40%
Interpretation may be
limited by falsely low
FVC
no
Is FVC reduced?
no
yes
Restriction may be present;
Need TLC to definitively
diagnose restriction
Normal pulmonary
mechanics
Restriction
Spirometry:
Severity is determined
by the reduction in VC
Mild
70-80%
Moderate
60-70%
Severe
<60%
Lung volumes:
Severity determined by
the reduction in TLC
Mild
65-80%
Moderate
50-65%
Severe
<50%
Algorhithim for PFT's:
What do the results mean: Algorhithim for PFT's
Is the FEM adequate?
no
yes
Is the FEV1/FVC
lower than predicted?
yes
This is the definition of
obstruction
Mild
FEV1 >70%
Moderate FEV1 60-70%
Mod severe FEV1 50-60%
Severe
FEV1 <50%
Very severe FEV1 <40%
Interpretation may be
limited by falsely low
FVC
no
Is FVC reduced?
no
yes
Restriction may be present;
Need TLC to definitively
diagnose restriction
Normal pulmonary
mechanics
Restriction
Spirometry:
Severity is determined
by the reduction in VC
Mild
70-80%
Moderate
60-70%
Severe
<60%
Lung volumes:
Severity determined by
the reduction in TLC
Mild
65-80%
Moderate
50-65%
Severe
<50%
What do the results mean:
Algorhithim for PFT's
Step 2, what is the of FEV1 /FVC?- aka FEV1%
• If it is reduced, then by definition there is
airway obstruction
– Any reduction compared to the predicted value
• The severity of is determined by the FEV1
–
–
–
–
–
–
≥80% is considered “normal”
70-80% is considered mild
60-70% is considered moderate
50-60% is considered moderately severe
40-50% is considered severe
<40% is very severe
What do the results mean: Algorhithim for PFT's
Is the FEM adequate?
no
yes
Is the FEV1/FVC
lower than predicted?
yes
This is the definition of
obstruction
Mild
FEV1 >70%
Moderate FEV1 60-70%
Mod severe FEV1 50-60%
Severe
FEV1 <50%
Very severe FEV1 <40%
Interpretation may be
limited by falsely low
FVC
no
Is FVC reduced?
no
yes
Restriction may be present;
Need TLC to definitively
diagnose restriction
Normal pulmonary
mechanics
Restriction
Spirometry:
Severity is determined
by the reduction in VC
Mild
70-80%
Moderate
60-70%
Severe
<60%
Lung volumes:
Severity determined by
the reduction in TLC
Mild
65-80%
Moderate
50-65%
Severe
<50%
Be careful before citing “restrictive deficits” in people
with obstructive lung disease
TLC
TLC
Vt
Vt
VC
FRC
RV
Emphysema
FRC
VC
RV
Normal
Algorhithim for PFT's:
Algorhithim for PFT's
If FEV1/FVC is normal
• Is FVC normal?
• If yes then the subject has “normal
pulmonary mechanics”
• If not, then is there any reason to suspect
restrictive disease?
– Keep in mind…a poor FEM (which affects the
FVC more than the FEV1) not only
underestimates FVC, but overestimates
FEV1/FVC, and can lead to false negative
spirometry for airway obstruction
Restrictive lung disease
By definition means a reduced total
lung capacity
TLC
Vt
FRC
VC
RV
Reduced vital capacity can suggest restriction
What do the results mean:
Algorhithim for PFT's
Restrictive lung disease
• This can only be definitively
established by measurements of lung
volume
– Gas dilution methods
• Only measures gas in communication with
the environment
– Plethysmography
• Measure total thoracic gas volume, but is
more cumbersome
• Normal FEV1/FVC and reduced FVC with a good
FEM can infer the presence of restrictive defect
What do the results mean:
Algorhithim for PFT's
Assessing severity of restrictive defects
• Without TLC measurement, base severity on the
FVC
– ≥80% is considered “normal”
– 70-80% is considered mild
– 60-70%% is considered moderate
– 60% is considered severe
• When TLC is measured
– Gold standard to define restrictive ventilatory
defect
– Only order “Full PFTs” if you suspect
restrictive or interstitial lung disease
(expensive!)
What do the results mean:
Algorhithim for PFT's
Restrictive defects cont’d
• Severity is based on the degree of
impairment in TLC
–≥80% is considered “normal”
–65-80% is considered mild
–50-65% is considered moderate
–<50% is considered severe
What do the results mean: Algorhithim for PFT's
Is the FEM adequate?
no
yes
Is the FEV1/FVC
lower than predicted?
yes
This is the definition of
obstruction
Mild
FEV1 >70%
Moderate FEV1 60-70%
Mod severe FEV1 50-60%
Severe
FEV1 <50%
Very severe FEV1 <40%
Interpretation may be
limited by falsely low
FVC
no
Is FVC reduced?
no
yes
Restriction may be present;
Need TLC to definitively
diagnose restriction
Normal pulmonary
mechanics
Restriction
Spirometry:
Severity is determined
by the reduction in VC
Mild
70-80%
Moderate
60-70%
Severe
<60%
Lung volumes:
Severity determined by
the reduction in TLC
Mild
65-80%
Moderate
50-65%
Severe
<50%
What do the results mean:
Algorhithim for PFT's
What about flow-volume loops?
V
o
l
u
m
e
F
l
o
w
Lung Volume
Time (sec)
Flow volume loop examples
What are these?
Inspiratory
effort
Expiratory
effort
What do the results mean:
Diffusing capacity aka DLCO
• Measures the ability of the lung to
transfer gas from the environment to
the bloodstream
• DLCO=VCO/(PACO-PaCO)
– Measures the volume of gas that moves
across the alveolar-capillary barrier per
unit of time per mm Hg gradient
What do the results mean:
What factors affect DLCO?
• Non-disease related
– Age, body size, lung volume, hemoglobin
concentration, body position, patient
cooperation, altitude, tobacco use, etc., etc.
• Disease related-anything that affects
the lung parenchyma or hemoglobin
in the lungs
– Emphysema (Very sensitive), but not asthma or chronic
bronchitis
– Pulmonary vascular disease
– Infiltrative/interstitial lung diseases (Very sensitive)
• Sarcoid, IPF, BOOP, hypersensitivity pneumonitis
• Others..CHF (Increased?), pulmonary hemorrhage
(increased)
What do the results mean:
DLCO?
• Because of the number of factors affecting
the test there is a wider variation
– Normal is considered ≥75%
– Less than 75% is “reduced”
– Less than 40% is commonly associated
with resting or exercise induced
hypoxemia and should prompt you to
evaluate the patient for supplemental
oxygen
What can PFTs tell you about
the patient
• Normal or abnormal
• What diseases can you diagnose?
– Only asthma is defined by its PFTs
• Estimation of impairment, or severity
of disease
• Response to therapy
• Occupational surveillance
What PFTs cannot tell you
• Does the degree of abnormality
explain the patients symptoms?
• “Normality” does not exclude the
presence of disease
• Abnormal test may not reflect loss of
lung function
49 year old man with aplastic
anemia, awaiting BMT; May 1997
BASELINE
LUNG MECHANICS
Actual
%Pred
FVC
liters
5.03
98%
FEV1
liters
3.77
97%
FEV1/FVC
%
75%
76%
Actual
%Pred
LUNG VOLUMES
RV pleth
liters
1.81
87%
TLC pleth
liters
6.96
97%
RV/TLC pleth
%
26%
One month after BMT
LUNG MECHANICS
Actual
Pred
%Pred
FVC
liters
2.98
5.12
58%
FEV1
liters
2.31
3.90
59%
FEV1/FVC
%
78%
76%
102%
Actual
Pred
%Pred
14.60
82%
%Pred
DIFFUSION
Hgb
mg/dl
12.00
COHgb
%
2.30
MUSCLE FORCES
Actual
Pred
Pemax
cmH2O
150.00
216 +/- 45
Pimax
mcH2O
-60
-127 +/- 28
SUPINE
FVC
FEV1
FEV1/FVC
Actual
1.31
0.85
65%
%Pred
26%
22%
85%
%Chg
-56%
-63%
-16%
49 year old man with aplastic anemia, 8
months after BMT; February 1998
LUNG MECHANICS
Actual
Pred
%Pred
FVC
liters
3.71
5.12
72%
FEV1
liters
2.59
3.90
66%
FEV1/FVC
%
70%
76%
92%
71 year old man with 2 year
history of dyspnea; June 2002
LUNG MECHANICS
FVC
liters
FEV1
liters
FEV1/FVC
%
Actual
1.30
0.82
67%
Pred
4.09
2.72
68%
%Pred
32%
30%
100%
71 year old man with 2 year
history of dyspnea; August 2002
LUNG MECHANICS
FVC
liters
FEV1
liters
FEV1/FVC
%
Actual
2.71
2.09
77%
Pred
4.02
2.69
68%
%Pred
67%
78%
115%
Extrathoracic/upper airway
obstruction (stridor)
Fixed upper airway obstruction
PFT summary
• Check the FEM to make sure it is adequate
• Obstructive ventilatory defects are defined
by FEV1/FVC less than predicted
– Severity graded by degreee of impairment in FEV1
• Restrictive ventilatory defect is defined by
reduced TLC
– Reduced FVC with no obstruction and a good FEM
suggests the presence of a restrictive deficit
• DLCO is abnormal in almost all
parenchymal lung diseases