Restrictive Lung Disease USMLE Step 1 Practice Question
A 67-year-old man with a 40-year history of occupational asbestos exposure presents to clinic with progressive dyspnea on exertion over the past 2 years. He denies chest pain, orthopnea, or lower extremity edema. Vital signs: BP 138/82 mmHg, HR 92 bpm, RR 22/min, SpO2 92% on room air. Physical examination reveals end-inspiratory crackles at bilateral lung bases; no clubbing or cyanosis noted. Chest X-ray shows bilateral lower lobe pleural thickening and pleural plaques. Pulmonary function testing demonstrates: FVC 70% predicted, FEV1/FVC ratio 0.78, and DLCO 48% predicted. Echocardiography shows normal left ventricular ejection fraction. Which of the following mechanisms best accounts for the disproportionate reduction in diffusing capacity relative to lung volumes in this patient?
Answer choices
- AAsbestos-induced visceral pleural fibrosis with reduced alveolar-capillary surface areaCorrect answer
- BPulmonary edema secondary to diastolic dysfunction of the left ventricle
- CSmall airway disease causing air trapping and ventilation-perfusion mismatch
- DAsbestos fiber-induced pulmonary vasculitis with capillary obliteration
- EIntracardiac right-to-left shunt reducing effective pulmonary perfusion
- FAnemia of chronic disease reducing hemoglobin-dependent oxygen diffusion
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