Interpretation of Lung Function Test

Question 1

What are the pre-requisites for valid lung function test result?

Answer 1

1. Volume time curve reaches plateau and expiration lasts at least 6s
2. Results of the two best efforts (FEV1 and FVC) are within 0.2 L of each other
3. flow-volume loops are free of artifacts and abnormalities

P/S: flattened flow-volume loops:
- submaximal effort
- central or upper airway obstruction

Question 2

What are the steps to interpret lung function test?

Answer 2

A. Obstructive or restrictive pattern
- FEV1/FVC ratio
- FVC value
- Adjuncts: TLV, RV

B. Grading severity - ATS system or GOLD criteria

C. Obstructive reversibility
- Bronchodilators increases > 12% and/or 200mL

D. DLCO (or TLCO) - rate of gas diffusion from alveoli into blood (tested with carbon monoxide)

E. Transfer coefficient (KCO) - correction for lung volume with age

F. Bronchoprovocation
- Methacholine challenge
- Mannitol inhalation challenge
- Exercise testing
- Eucapnic voluntary hyperpnea testing

G. Compare past and current result - progression

Question 3

What is the lung function test of obstructive lung disease?

Answer 3

1. FEV1 significantly low
2. FVC normal or low
3. Result: FEV1/FVC low (< 70%)
4. TLC and RV increased (air trapping)
5. DLCO reduced
6. KCO reduced

Question 4

What is the lung function test of restrictive lung disease?

Answer 4

1. FEV1 low
2. FVC significantly low
3. Result: FEV1/FVC normal (>70%)
4. TLC and RV reduced
5. DLCO reduced
6. KCO reduced unless active haemorrhage or deformity