Define respiratory compliance (20% of marks). Describe the factors that affect it (80%
This question was generally well answered with good structure.
It is unclear how this college comment is an improvement on the absence of any comment. And if the question was answered so well, why was the pass rate only 54%? Fortunately, in their answer Question 1(p.2) from the second paper of 2008, the examiners listed their expectations of the essential components of an answer.
- Respiratory compliance is defined as the change in lung volume per unit change in transmural pressure gradient. It is usually about 100ml/cm H2O.
- Static compliance is defined as the change in lung volume per unit change in pressure in the absence of flow. It is composed of:
- Chest wall compliance (usually 200ml/cm H2O.
- Lung tissue compliance (also usually cm H2O.)
- Dynamic compliance is defined as the change in lung volume per unit change in pressure in the presence of flow. Its components are
- Chest wall compliance
- Lung tissue compliance
- Airway resistance (which makes it frequency-dependent)
- Specific compliance is compliance that is normalized by a lung volume, usually FRC. It is used to compare compliance between lungs of different volumes (eg. child and adult)
|Lung compliance||Chest wall compliance|
Increased lung compliance
Increased chest wall compliance
Decreased static lung compliance
Decreased dynamic lung compliance
Decreased chest wall compliance
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