Asthma USMLE Step 1 Practice Question
A 67-year-old man with severe lobar pneumonia presents with profound hypoxemia (SpO2 78% on room air). Vital signs show BP 142/88, HR 118, RR 28, Temp 39.2°C. Chest X-ray demonstrates left lower lobe consolidation with air bronchograms. Bronchoscopy reveals complete obstruction of a segmental bronchus by purulent material while perfusion to that region remains intact. He denies recent chest pain. Which of the following best describes the ventilation-perfusion physiology in the affected region?
Answer choices
- APure hypoventilation with a normal A a gradient across the whole lung
- BReduced diffusion only with preserved ventilation and perfusion
- CV Q ratio of 1 representing normal gas exchange
- DV Q ratio of infinity representing dead space
- EV Q ratio of 0 representing shunt physiologyCorrect answer
- FV Q ratio of 0.1 representing a low ventilation-perfusion mismatch
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