Physiologyniche
A 24-year-old man reports 12 months of increasing breathlessness on exertion. He climbs stairs slowly and pushes on his thighs to stand from a low chair. His cough sounds ineffective. He smokes 10 cigarettes daily. He is 175 cm tall and weighs 71 kg. The chest wall is symmetrical with no spinal curvature, and breath sounds are normal. Lung function testing shows: FEV1 1.9 L (48% predicted); FVC 2.3 L (48% predicted); FEV1/FVC ratio 0.83 (predicted 0.83); total lung capacity 4.9 L (74% predicted); residual volume 2.6 L (152% predicted); carbon monoxide transfer factor 9.1 mmol/min/kPa (94% predicted).
Which one of the following best accounts for this man's pattern of lung volumes?