Idiopathic Pleuroparenchymal Fibroelastosis

A 56-year-old non-smoking woman presents with 2 years of progressive dry cough, exertional dyspnea, and marked weight loss. Examination reveals a characteristic flattened thorax (platythorax) with fine inspiratory crackles over the upper posterior chest. She has had two episodes of spontaneous pneumothorax requiring drainage. High-resolution CT shows biapical pleural thickening with subpleural fibroelastosis concentrated in the upper lobes. Spirometry is shown in the diagram. The FEV1/FVC ratio marked **C** is 0.88 (preserved/elevated). What does this preserved FEV1/FVC ratio in the context of markedly reduced FVC and DLCO indicate about the pattern of lung dysfunction in this patient?