Bird Fancier Hypersensitivity Pneumonitis Restrictive Spirometry

A 55-year-old female avid pigeon breeder presents with 4 months of progressive exertional dyspnea, dry cough, and low-grade fever. She spends 3–4 hours daily in her home aviary. High-resolution CT shows bilateral poorly-defined centrilobular ground-glass nodules with mosaic attenuation and mid-to-upper lobe predominance. Serum precipitating IgG antibodies against pigeon antigens are strongly positive. Pulmonary function testing reveals the spirometric pattern marked **A** in the diagram. Which of the following best explains the physiologic basis of this pattern in bird fancier hypersensitivity pneumonitis?