Why does reduced pulmonary capillary transit time diminish oxygen uptake when the ventilation-perfusion ratio is already elevated?

💡 Explanation

Reduced transit time limits the opportunity for red blood cells to fully saturate with oxygen as they pass through the pulmonary capillaries, because diffusion equilibrium is not reached quickly enough. Therefore, less oxygen is picked up, rather than a surface area reduction or changes to hemoglobin's affinity for other gases.

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