Dynamic Airway Narrowing

A 61-year-old man who reported progressive exertional dyspnea of 12 years' duration received a diagnosis of chronic obstructive pulmonary disease on the basis of a 150-pack-year history of smoking, emphysema on radiographic evaluation, and a forced expiratory volume in one second of 0.72 liter (28.8 percent of the predicted value). An upper thoracic high-speed electron-beam computed tomographic scan showed small airways (approximately 3 mm in diameter) that were open during inspiration (Panel A, arrows) but extremely narrow during expiration (Panel B, arrows). Dynamic narrowing of the airways is common in patients with chronic obstructive pulmonary disease and is caused by . . .