COPD USMLE Step 1 Practice Question
A 48-year-old woman with severe obesity and a 40 pack-year smoking history presents with morning headaches and daytime somnolence. Vital signs show BP 148/92 mmHg, HR 102 bpm, RR 18/min, SpO2 88% on room air. She reports progressive dyspnea and denies orthopnea. Arterial blood gas while awake reveals pH 7.33, PaCO2 58 mmHg, and PaO2 66 mmHg. Chest X-ray shows hyperinflation without focal infiltrates. Which of the following best explains this patient's gas exchange abnormality?
Answer choices
- ARight to left shunt from pulmonary arteriovenous malformations
- BLoss of elastic recoil causing dynamic airway collapse
- CSelective diffusion limitation due to thickened alveolar walls
- DChronic alveolar hypoventilation causing hypercapniaCorrect answer
- EAcute increase in physiologic dead space from thromboembolism
- FVentilation-perfusion mismatch from bullae rupture causing pneumothorax
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