Restrictive Lung Disease USMLE Step 1 Practice Question
A 65-year-old man with progressive idiopathic pulmonary fibrosis presents with marked exertional dyspnea. Vital signs show BP 138/82 mmHg, HR 92 bpm, RR 18/min, temperature 37.2°C, and resting SpO2 98% on room air. During a 6-minute walk test, SpO2 drops to 88%. High-resolution CT chest shows bilateral lower-lobe predominant reticular opacities with traction bronchiectasis. Pulmonary function tests reveal reduced DLCO. He denies orthopnea. Which mechanism best explains the oxygen desaturation with exertion?
Answer choices
- AObstructive ventilatory defect
- BPulmonary embolism
- CDecreased diffusion capacity due to interstitial thickeningCorrect answer
- DTransudative pleural effusion from congestive heart failure
- EAspiration pneumonia due to anaerobes
- FVentilation-perfusion mismatch from bronchospasm-induced airway collapse
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