During intensive exercise, blood transit time through alveolar capillaries decreases. Why does arterial oxygen saturation remain relatively stable despite the reduced transit time?

💡 Explanation

Arterial oxygen saturation remains stable because diffusion equilibrium between alveolar air and capillary blood is normally achieved rapidly (within approximately 0.25 seconds), therefore even reduced transit times (still exceeding 0.25s) allow sufficient oxygen uptake, rather than being limited by reaction kinetics or ventilation.

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