Unknown In a healthy subject, when is the PO2 of the blood leaving a pulmonary capillary lower than the PO2 in the alveolus served by that capillary? A While breathing a low O2 gas mixture B While performing an exercise in which the cardiac output doubles C At the base of the lungs, where perfusion exceeds ventilation D None of the above 💡 Explanation In a healthy subject, when is the PO2 of the blood leaving a pulmonary capillary lower than the PO2 in the alveolus served by that capillary? ✓ Correct Answer: D. None of the above