A 58-year-old male smoker presents to the pulmonology clinic with a 3-year history of progressive dyspnea on exertion and chronic cough productive of scanty sputum. He denies hemoptysis or chest pain. Physical examination reveals barrel chest, pursed-lip breathing, and prolonged expiratory phase. Spirometry shows FEV₁ = 52% predicted, FVC = 78% predicted, FEV₁/FVC ratio = 0.58. Total lung capacity (TLC) is 125% predicted, and residual volume (RV) is 180% predicted. Which of the following best explains the spirometric pattern observed in this patient?