1. Pulmonary function test
Tests of respiratory mechanics
&
Tests of pulmonary gas exchange

2. Indications
 Evaluation of dyspnea, cough, abnormal CxR
 Quantitative assessment of severity of
pulmonary disease
 Screening for early disease
 Longitudinal surveillance of OLD
 Follow-up of disease activity
 Assessment of bronchodilator response
 Prediction of surgical risk
 Quantitate disability

3. Tests of respiratory
mechanics
Spirometry (PFT)
Body plethysmography or
He dilution method- FRC

4. Spirometry
 Deep inspirationForced expiration Deep
inspiration
 Requires patient cooperation
 Adequate test-
 Smooth flow-volume loop
 Exhalation x ~6 seconds
 At least 3 readings, maximum 8
 2 largest FVC & FEV1 within 0.2 L

5. Definitions
 Total lung capacity- TLC-
 Volume of gas after maximal inspiration
 Residual volume- RV-
 Volume of gas after maximal expiration
 Vital capacity- VC-
 TLC - RV
 Forced vital capacity- FVC-
 Total volume exhaled
 Forced expiratory vol. in 1st
sec.- FEV1-
 Volume exhaled during 1st
second of expiration

6. Diagram
 Lung volumes
 Flow-volume loop

7. Results & patterns
 Results-
 Absolute numbers- in litres or litres per second
 % predicted for height, age, sex, weight- >80% is normal
 Obstructive- asthma, COPD
 FEV1 decreased due to increased airway resistance
 FVC may be decreased due to air trapping
 Ratio FEV1/FVC is decreased
 Restrictive- fibrosis, ILD
 TLC reduced
 FEV1 & FVC reduced proportionally
 Ratio FEV1/FVC remains normal

8. Tests of gas exchange
 Diffusing capacity for CO- DLco-
 Low in pulmonary vascular diseases- PHT, PE
 Low in diffuse lung diseases- fibrosis, emphysema
 Pulse oximetry- correlates with SaO2
 ABG- for PaO2, PaCO2, pH
 Hypoxemia- PaO2 <60 mm Hg ~ SaO2 <90%
 Hypercapnia- PaCO2 >45 mm Hg = hypoventilation
 Hypocapnia- PaCO2 <35 mm Hg = hyperventilation

9. Hypoxia
 V/Q mismatch- asthma, COPD, ILD,
pneumonia, pulmonary vascular disease
 Commonest cause
 Elevated (A-a)DO2, normal PaCO2
 Responds to supplemental O2
 RL shunt- intracardiac or intrapulmonary
 Elevated (A-a)DO2
 Doesn’t respond to supplemental O2
 Hypoventilation- CNS/neuromuscular causes
 Increased PaCO2, normal (A-a)DO2
 Reduced inspired oxygen (PiO2)- high
altitude

10. Hypoxia
 V/Q mismatch- asthma, COPD, ILD,
pneumonia, pulmonary vascular disease
 Commonest cause
 Elevated (A-a)DO2, normal PaCO2
 Responds to supplemental O2
 RL shunt- intracardiac or intrapulmonary
 Elevated (A-a)DO2
 Doesn’t respond to supplemental O2
 Hypoventilation- CNS/neuromuscular causes
 Increased PaCO2, normal (A-a)DO2
 Reduced inspired oxygen (PiO2)- high
altitude