During high-intensity exercise, some individuals exhibit reduced arterial oxygen saturation despite increased ventilation. Which mechanism explains why efficient gas exchange fails to maintain adequate oxygen levels?

💡 Explanation

Diffusion limitation occurs because the transit time of red blood cells through pulmonary capillaries is reduced at high cardiac outputs. This decreased transit time means oxygen doesn't fully equilibrate, therefore arterial saturation drops, rather than being limited by cardiac output or metabolic shifts that primarily affect oxygen unloading at tissues.

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