Expansion
Loss of elastic recoil, airway collapse, gas trapping and impaired gas exchange
Expansion
Two overlapping processes:
Emphysema - destruction of alveolar walls
- Loss of elastic recoil, so reduced driving pressure for expiration
- Loss of radial traction tethering small airways open, so they collapse on expiration
- Loss of alveolar surface area and capillary bed, reducing diffusing capacity
Chronic bronchitis - mucus hypersecretion and airway inflammation
Consequences:
- Gas trapping and hyperinflation, flattening the diaphragm and raising the work of breathing
- V/Q mismatch causing hypoxaemia
- Hypoxic pulmonary vasoconstriction raising pulmonary artery pressure, leading to cor pulmonale
- Eventually carbon dioxide retention with renal bicarbonate compensation
Pursed lip breathing is a learned compensation, raising airway pressure to keep airways open, and hyperinflation itself partly compensates by increasing airway diameter. Both are why patients often adopt a characteristic posture and breathing pattern.