A 38-year-old never-smoker from North Europe presents with 2 years of progressive exertional dyspnea and dry cough. Family history is significant for early emphysema in his brother (age 42) and cirrhosis in his father (age 60). HRCT chest shows bilateral lower-lobe panacinar emphysema. Serum alpha-1 antitrypsin is 22 mg/dL (normal 100–200) with PiZZ genotype confirmed. The flow-volume loop shown displays the finding marked **A** — severe expiratory concavity with markedly reduced peak expiratory flow and prolonged expiratory tail. Which of the following best explains the pathophysiology underlying this spirometric pattern in alpha-1 antitrypsin deficiency?