1. 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)

2. 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)

3. Lung Cancer ARDS Inside the mind of a pulmonologist?? Pneumonia
Autoimmune/Vasculitis
ARDS
Environmental/Occupational
TB and other Mycobacterial disease
Pulmonary vascular disease
Inside the mind of a pulmonologist??
Sleep
apnea
Obstructive
Lung Diseases
Restrictive
Golf, Cubs,
College
basketball
Pneumonia

4. Why measure PFTs? Why do any test? To look for disease
To evaluate severity of disease
To determine response to treatment
To prevent disease

5. 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

6. 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

7. Normal anatomy Medium airways…. Small airways….
Alveoli…gas exchange units

8. Large airways and chest wall

9. 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

11. ERV/IRV Expiratory/Inspiratory reserve volume
Vt Tidal volume
VC Vital Capacity
ERV/IRV Expiratory/Inspiratory reserve volume
These are all measured easily with spirometers
FRC Functional residual capacity
RV residual volume
TLC Total lung capacity (RV + VC)
Measuring these requires more specialized equipment

12. TLC RV
ERV IC
TLC VC Vt VC
FRC RV RV
Normal

13. Vital capacity is reduced in both obstructive and restrictive diseasesVC VC VC RV RV RV
Obstructive
Normal
Restrictive

14. 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

15. Spirometry
Spirometry requires that you perform a forced expiratory maneuver (FEM)

16. 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

17. 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)

18. Body plethysmograph

19. Plungx Vlung=P’lungx V’lung
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
V’box =Vbox+∆V
P’box =Pbox+∆P
Plung
Vlung
Plungx Vlung=P’lungx V’lung
V’lung = Vlung +∆V
P’lung =Plung+∆P
Pbox x Vbox

20. Why measure residual volume
Why measure residual volume? Look at two people with identical vital capacity
TLC
TLC Vt Vt VC
FRC VC RV
FRC RV

21. Summary What we measure Why we measure it How we measure
Airflow, and gas exchange
Why we measure it
Diagnose, follow treatment, prognosticate
How we measure
What do you do with the results?

22. What do the results mean
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

23. 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

25. What do the results mean: Algorhithim for PFT's
Is the FEM adequate? y e s n o
Is the FEV1/FVC lower than predicted?
Interpretation may be limited by falsely low FVC y e s n o
This is the definition of obstruction
Mild FEV1 >70%
Moderate FEV %
Mod severe FEV %
Severe FEV1 <50%
Very severe FEV1 <40%
Is FVC reduced? y e s n o
Restriction may be present; Need TLC to definitively diagnose restriction
Normal pulmonary mechanics
Restriction
Spirometry:
Lung volumes:
Severity is determined
Severity determined by
by the reduction in VC
the reduction in TLC
Mild
70-80%
Mild
65-80%
Moderate
60-70%
Moderate
50-65%
Severe
<60%
Severe
<50%

26. Algorhithim for PFT's:

27. What do the results mean: Algorhithim for PFT's
Is the FEM adequate? y e s n o
Is the FEV1/FVC lower than predicted?
Interpretation may be limited by falsely low FVC y e s n o
This is the definition of obstruction
Mild FEV1 >70%
Moderate FEV %
Mod severe FEV %
Severe FEV1 <50%
Very severe FEV1 <40%
Is FVC reduced? y e s n o
Restriction may be present; Need TLC to definitively diagnose restriction
Normal pulmonary mechanics
Restriction
Spirometry:
Lung volumes:
Severity is determined
Severity determined by
by the reduction in VC
the reduction in TLC
Mild
70-80%
Mild
65-80%
Moderate
60-70%
Moderate
50-65%
Severe
<60%
Severe
<50%

29. 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

31. What do the results mean: Algorhithim for PFT's
Is the FEM adequate? y e s n o
Is the FEV1/FVC lower than predicted?
Interpretation may be limited by falsely low FVC y e s n o
This is the definition of obstruction
Mild FEV1 >70%
Moderate FEV %
Mod severe FEV %
Severe FEV1 <50%
Very severe FEV1 <40%
Is FVC reduced? y e s n o
Restriction may be present; Need TLC to definitively diagnose restriction
Normal pulmonary mechanics
Restriction
Spirometry:
Lung volumes:
Severity is determined
Severity determined by
by the reduction in VC
the reduction in TLC
Mild
70-80%
Mild
65-80%
Moderate
60-70%
Moderate
50-65%
Severe
<60%
Severe
<50%

33. RV RV TLC TLC Vt Vt VC FRC VC FRC
Be careful before citing “restrictive deficits” in people with obstructive lung disease
TLC
TLC Vt Vt VC
FRC VC RV
FRC RV
Emphysema
Normal

34. Algorhithim for PFT's:

35. 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

36. Restrictive lung disease
By definition means a reduced total lung capacity
Reduced vital capacity can suggest restriction
TLC V t VC
FRC RV

37. 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

38. 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!)

39. Severity is based on the degree of impairment in TLC
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

40. What do the results mean: Algorhithim for PFT's
Is the FEM adequate? y e s n o
Is the FEV1/FVC lower than predicted?
Interpretation may be limited by falsely low FVC y e s n o
This is the definition of obstruction
Mild FEV1 >70%
Moderate FEV %
Mod severe FEV %
Severe FEV1 <50%
Very severe FEV1 <40%
Is FVC reduced? y e s n o
Restriction may be present; Need TLC to definitively diagnose restriction
Normal pulmonary mechanics
Restriction
Spirometry:
Lung volumes:
Severity is determined
Severity determined by
by the reduction in VC
the reduction in TLC
Mild
70-80%
Mild
65-80%
Moderate
60-70%
Moderate
50-65%
Severe
<60%
Severe
<50%

41. What do the results mean: Algorhithim for PFT's What about flow-volume loops?
Lung Volume
Time (sec)

42. Flow volume loop examples

43. What are these?

44. Inspiratory effort
Expiratory effort

45. 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

46. 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)

47. 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

48. 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

49. 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

50. 49 year old man with aplastic anemia, awaiting BMT; May 1997
BASELINE 
LUNG MECHANICS
Actual
%Pred
FVC
liters 
5.03  
98% 
FEV1
3.77  
97% 
FEV1/FVC % 
75% 
76% 
LUNG VOLUMES
RV pleth
1.81  
87% 
TLC pleth
6.96  
RV/TLC pleth
26% 

51. One month after BMT LUNG MECHANICS Actual Pred %Pred FVC liters 2.98
2.98  
5.12  
58% 
FEV1
2.31  
3.90  
59% 
FEV1/FVC % 
78% 
76% 
102% 
DIFFUSION
Hgb
mg/dl 
12.00  
14.60  
82% 
COHgb
2.30  
MUSCLE FORCES
Actual
Pred
%Pred
Pemax
cmH2O   
216 +/- 45 
Pimax
mcH2O 
-60  
-127 +/- 28 
SUPINE 
Actual
%Pred
%Chg
1.31  
26% 
-56% 
0.85  
22% 
-63% 
65% 
85% 
-16% 
FVC
FEV1
FEV1/FVC

52. 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
2.59  
3.90  
66% 
FEV1/FVC % 
70% 
76% 
92% 

53. 71 year old man with 2 year history of dyspnea; June 2002
LUNG MECHANICS
Actual
Pred
%Pred
FVC
liters 
1.30 
4.09 
32% 
FEV1
0.82 
2.72 
30% 
FEV1/FVC % 
67% 
68% 
100% 

54. 71 year old man with 2 year history of dyspnea; August 2002
LUNG MECHANICS
Actual
Pred
%Pred
FVC
liters 
2.71 
4.02 
67% 
FEV1
2.09 
2.69 
78% 
FEV1/FVC % 
77% 
68% 
115% 

56. Extrathoracic/upper airway obstruction (stridor)

57. Fixed upper airway obstruction

58. 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