Pulmonary function tests (PFTs) are used to characterize and monitor pulmonary disease. Common PFTs include spirometry to assess airflow limitation, lung volume measurements to detect restriction, diffusion capacity to evaluate gas exchange, and bronchoprovocation tests to identify airway hyperresponsiveness. Spirometry yields values like FEV1, FVC, and their ratio that are used to classify obstructive and restrictive patterns. Lung volumes are directly measured using techniques like plethysmography and indirectly calculated from spirometry. Diffusion capacity reflects membrane thickness and surface area via carbon monoxide transfer. PFTs provide objective data to diagnose and manage respiratory conditions.

1. Pulmonary
Function Testing

2. Goals
• Indications for PFTs
• Know types of studies that can be
ordered
• Understand how common tests are done
• Interpretation of the data

3. Indications
• Characterize known or suspected pulmonary
disease (COPD screening)
• Follow evolution of pulmonary disease
• Assess effectiveness of therapy
• Pre-op assessment of surgical risks
• Assess need for surgical interventions
• Assess impact of an occupational exposure

4. Pulmonary Function Tests
• Spirometry/flow-volume loop
• Lung volumes
• Diffusion capacity
• Arterial blood gas, shunt fraction measurement, dead
space
• Airway resistance
• Inspiratory/expiratory muscle pressures
• Airway reactivity (methacholine/exercise challenge)
• Cardiopulmonary exercise test

5. Normal Lung Volumes and
Capacities

6. Primary Lung Volumes
• VT: tidal volume - air inhaled during quiet
breathing
• IRV: inspiratory reserve volume - maximal
volume inhaled from quiet breathing
• ERV: expiratory reserve volume - maximal
volume exhaled from quiet breathing
• RV: residual volume - volume remaining after
maximal exhalation

7. Lung Capacities = Sum of
Primary Lung Volumes
• TLC: total lung capacity - sum of 4 primary
volumes
• VC: vital capacity - volume exhaled from
maximal inspiration to maximal expiration
• FRC: functional residual capacity – resting,
end-expiratory volume
• IC: maximal volume inhaled from FRC

8. The Spirogram

9. Spirometry
and Flows
FEF 25-75%: mean
forced expiratory
flow during middle
half of FVC;
sensitive to small
airways disease

10. Flow/Volume
Loops
Includes inspiratory and
expiratory flows
Instantaneous flows
Shape of curve
restrictive vs. obstructive

12. Normal Reference
• Normal standards depend upon:
– Height
– Gender
– Age
– Race
• Reproducibility criteria (3 trials examined)
• Rate of decline: normal fall in FEV1 with
age = 20-30cc/year; in COPD = 50-
80cc/year

13. Classification of Impairment

14. Interpretation of Spirometry
• Step 1: obstruction or not?
– Low FEV1/FVC (<70%) = obstruction
• Step 2: Interpret severity (based upon FEV1)
• Restriction: FEV1 and FVC reduced in proportion
(i.e. normal FEV1/FVC ratio)
• Flow/Volume Loops
– Obstruction – concave, scooped appearing
– Restriction – decreased VC, normal shape
– Upper airway obstruction: cut-off insp and/or exp limbs

15. Bronchodilator Response:
• Response to inhaled bronchodilators:
– Typical in asthma; some patients with COPD
and CF have reversibility also
– “Real response”: consists of a change in FEV1
by at least 12% (and 200cc) after inhalation of
albuterol

16. Broncho-provocation testing
• Reveals airway hyper-reactivity (asthma)
• Useful to assess non-specific hyperrresponsiveness in a
patient with symptoms c/w asthma, but without
obstruction or bronchodilator reversibility (cough
variant asthma, exercise-induced asthma)
• Methacholine – 75% asthmatics will react
• Histamine – 90-95% asthmatics will react
• Decline in FEV1 by 20% at concentration of 8mg/ml or
less (methacholine)

17. Flow-volume loops and upper
airway obstruction
• Extrathoracic obstruction – vocal cord
dysfunction, goiter, cause flattening of
inspiratory limb of flow/volume loop
• Intrathoracic obstruction – bronchogenic cancer
in right mainstem bronchus, flattening of
expiratory limb of flow/volume loop

18. Intrathoracic Obstruction
Extrathoracic Obstruction

19. Lung Volumes
• Spirometry measures volume differences
between identifiable lung capacities (TLC, FRC,
RV), but cannot measure the absolute volume of
these key volumes
• Lung volumes measure FRC and use spirometry
to calculate TLC and RV
• FRC can be measured by following techniques:
– Closed circuit helium dilution
– Open circuit nitrogen washout
– Plethysmography or body box

20. Dilution Techniques
• Closed circuit helium dilution – starting at FRC, patient
breathes helium for 7 minutes (until equilibrium) from known
volume system with known He concentration; measure helium
concentration after maneuver
• Open nitrogen washout – starting at FRC, begin inspiring
100% O2 and collect/measure all nitrogen exhaled from the
lungs for 7 minutes (N2 essentially washed out). Given
known initial concentration of nitrogen in the lungs (81%),
use the measured concentration and volume of nitrogen in
collected air to calculate the starting lung volume (FRC) at
end of maneuver
• Both techniques underestimate actual FRC if ventilation isn’t
homogeneous (i.e. obstructive lung disease)

21. Helium Dilution
Point A: 2 L of 10% He
Point B: 5% He now present in system; FRC must be 2L!

22. Plethysmography

23. Plethysmography
• Measures thoracic gas –performed at FRC
• Underlying principle: Boyle’s Law
– Patient sits in sealed box, patient pants against shutter that is
closed at FRC
– Alveolar pressure changes measured at mouth (presumes open
glottis/equal pressures);
– Box pressure changes measured with respiratory efforts –
proportional to lung volume increases/decreases due to
respiratory efforts
PV = (P + P)(V + V)
V = FRC

24. Lung Volume Determinants
• FRC:
– Lung and chest wall properties
• TLC:
– Lung and chest wall properties
– Inspiratory muscle strength
• RV:
– Lung and chest wall properties
– Expiratory muscle strength
– Airway Closure**

25. Lung Volume Patterns
TLC
FRC
RV
ERV
IC

26. Diffusion
• Volume of gas transferred across
alveolar/capillary membrane/per minute/mmHg
of difference between the alveolar and capillary
blood
• Determined from CO uptake during 10 seconds
of breath-holding
• VCO = (Area/Thickness) x (Solubility/ MW) x
(PA-PC)

27. Diffusion – use of CO
• Rate of transfer of CO across respiratory membrane
relates to hemoglobin affinity (240 fold higher than for
O2)
• CO transfer rate decreases in anemia and increases in
polycythemia
• DLCO is artificially low in smokers (have baseline CO
in blood – i.e. concentration gradient working against
CO uptake)
• High altitude – increased transfer of CO

28. Diffusion
Loss of membrane surface area; increase in
thickness:
• pneumonectomy, emphysema, interstitial disease, CHF
Changes in Pulmonary Circulation
• Pulmonary vascular disease
Increases in DLCO
• pulmonary hemorrhage, left-to-right intracardiac
shunts, asthma

29. Pulmonary Gas Exchange
• Evaluating Hypoxemia:
• Hypoxemia with normal A-a gradient: hypoventilation
• Hypoxemia with increased A-a gradient: V/Q
mismatch, right-to-left shunt, diffusion impairment
• P(A-a)O2 = [PiO2 –(PaCO2/R)] – PaO2
• P(A-a)O2 = [0.21(PB-47) – (PaCO2/0.8)] –PaO2
• P(A-a)O2 = 150 – (PaCO2/0.8) – PaCO2

30. Case 1
• FVC 75% pred; FEV1 60% pred; ratio 64%
• TLC: 125% pred; FRC 120% pred; RV 160%
• DLCO: 30% pred
• ABG: 7.42/42/70 on RA

31. Case 2
• FVC 85% pred; FEV1 50% pred; ratio 55%
• TLC: 95% pred; FRC 105% pred; RV 145%
pred
• DLCO: 85%
• ABG: 7.37/48/58 on RA

32. Case 3
• FVC 65% pred; FEV1 68% pred; ratio 85%;
FEF25-75% 120% pred
• TLC 65% pred; FRC 65% pred; RV 70% pred
• Normal flow-volume shape
• DLCO 45% pred

33. Case 4
• FVC 85% pred; FEV1 71% pred; ratio 75%;
FEF25-75%45%
• TLC 85% pred; FRC 60% pred; RV 100%
pred; ERV 10% pred
• DLCO 85% pred

35. Flow-Volume Loops

36. Flow/Volume Loops in
Obstruction and Restriction

37. Broncho -
provocation
Agents

38. Mechanics
• Neuromuscular disease with MIP, MEP
• Pressure/volume – elastic properties of lung
• Esophageal balloon to measure changes in
expiratory lung volume with changes in
transpulmonary pressure
• Transpulmonary pressure = alveolar
pressure measured at mouth and pleural
pressure measured by balloon

39. Static Compliance
• volume/ pressure
• Mean compliance is 260cc/cm
• Interstitial lung disease – increased elastic
recoil, decreased compliance, less V/ P
• COPD – decreased elastic recoil, increased
compliance

40. Static
Compliance

41. Diffusion