A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 32-year-old woman presents with progressive shortness of breath and a dry cough. She says that her symptoms onset recently after a 12-hour flight. Past medical history is unremarkable. Current medications are oral estrogen/progesterone containing contraceptive pills. Her vital signs include: blood pressure 110/60 mm Hg, pulse 101/min, respiratory rate 22/min, oxygen saturation 88% on room air, and temperature 37.9℃ (100.2℉). Her weight is 94 kg (207.2 lb) and height is 170 cm (5 ft 7 in). On physical examination, she is acrocyanotic. There are significant swelling and warmth over the right calf. There are widespread bilateral rales present. Cardiac auscultation reveals accentuation of the pulmonic component of the second heart sound (P2) and an S3 gallop. Which of the following ventilation/perfusion (V/Q) ratios most likely corresponds to this patient’s condition?
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A
0.5Incorrect. V/Q of 0.5 indicates shunt physiology (less ventilation than perfusion), as in pneumonia/atelectasis — opposite of PE.
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B
1.3Correct. PE creates dead-space physiology (ventilation without perfusion), elevating V/Q above the normal ~0.8 — 1.3 reflects this shift.
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C
0.8Incorrect. 0.8 is the normal whole-lung V/Q ratio — would not be expected in PE.
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D
1Incorrect. V/Q of 1.0 is mildly elevated but doesn't reflect the pronounced increase seen in PE.
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E
2.0Incorrect. A V/Q of 2.0 represents extreme dead-space ventilation (essentially complete absence of perfusion to a ventilated unit) more typical of a massive saddle embolus than the segmental clot described here; 1.3 better fits the moderate V/Q shift in this presentation.
↑ Tap an answer to reveal the reasoning
Answer: B. This woman has classic risk factors for venous thromboembolism: oral contraceptive use, obesity, prolonged immobilization on a long flight, plus unilateral leg swelling/warmth (DVT) and acute dyspnea, tachycardia, hypoxia, low-grade fever, accentuated P2 (pulmonary hypertension), and an S3 gallop. This is pulmonary embolism.
In PE, the affected pulmonary segment receives ventilation but no perfusion because of vascular occlusion — creating physiologic dead space. The ventilation/perfusion (V/Q) ratio in PE rises above the normal ratio of ~0.8 (in the whole lung) because Q drops while V is preserved. A V/Q of 1.3 fits — the closest answer reflecting an increased V/Q ratio. Theoretically, V/Q in pure dead-space ventilation would approach infinity, but PE rarely creates complete obstruction in every segment, so a global increase to 1.3 is reasonable.
Key lung V/Q facts: normal V/Q ~0.8 overall, with apex V/Q ~3 (more ventilation than perfusion) and base V/Q ~0.6 (more perfusion than ventilation). Shunt (e.g., consolidation, atelectasis) has V/Q approaching 0 — perfusion without ventilation. Dead space (e.g., PE) has V/Q approaching infinity — ventilation without perfusion.
**Why each option:**
**A.** V/Q of 0.5 indicates shunt physiology (less ventilation than perfusion), as in pneumonia/atelectasis — opposite of PE.
**B.** Correct. PE creates dead-space physiology (ventilation without perfusion), elevating V/Q above the normal ~0.8 — 1.3 reflects this shift.
**C.** 0.8 is the normal whole-lung V/Q ratio — would not be expected in PE.
**D.** V/Q of 1.0 is mildly elevated but doesn't reflect the pronounced increase seen in PE.