Past Papers · SAQ
Respiratory Physiology — Obstructive PFTs
2011B Q18
Exam questionOutline the abnormalities in pulmonary function testing of a person with severe obstructive lung disease (40% marks). Describe the physiological changes that explain these abnormalities (60% marks).
CICMWrecks answer
Master answer
Obstructive Lung Disease
e.g. Asthma, COPD
| Pulmonary Function Test | Obstructive Lung Disease |
|---|---|
| Total lung capacity (TLC) | ↑ |
| Residual volume (RV) | ↑ |
| Forced vital capacity (FVC) | ↓ |
| Forced Expiratory Volume in 1st second (FEV1) | ↓↓ |
| FEV1 / FVC Ratio | ↓ , <80% |
| Maximum Voluntary Ventilation | ↓ |
| RV / TLC | ↑ |
| PEFR Peak Expiratory Flow Rate | ↓ |
| FEF 25-75% Forced expiratory flow at 25–75% of forced vital capacity | ↓ |
Physiological changes
- ↑ AWR caused by bronchial SM contraction, secretions, wall oedema, and reduced radial traction (from damaged lung parenchyma)
- Closing capacity rises towards or > FRC
- ↓ elastic potential energy is stored to generate driving pressure gradient (this is caused by ↑ lung compliance resulting from damaged lung parenchyma)
Thus
- ↓ FRMAX and ↓ steep rise in expiratory FR during effort-dependent part of the curve
- ↓ steep and “scooped” appearance of flow curve in effort-independent part of the curve due to dynamic airway compression occurring at higher lung volumes
Pulmonary function tests:
- Peak Flow
- Reduced PEF rates
- Simple spirometry:
- shows an increase in lung volumes
- decreased inspiratory capacity
- (increased FRC but not measured)
- Forced expired spirometry is diagnostic
- FEV1/FVC < 70%
- FEV1 % predicted <50%
- FEF 25 – 75% is prolonged
- Flow volume loops
- higher volumes
- decreased flow
- scooped effort dependent portion
Gladwin 2016
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2011B Q18 | Outline the abnormalities in pulmonary function testing of a person with severe obstructive lung disease (40% marks). Describe the physiological changes that explain these abnormalities (60% marks). | 0% |