Why does oxygen diffusion across the alveolar membrane decrease at high altitudes, even when the ventilation rate increases in a climber?

💡 Explanation

The reduced oxygen diffusion at high altitudes results from a lower partial pressure of oxygen in the atmosphere, which decreases the concentration gradient between the alveoli and pulmonary capillaries. Because the driving force for diffusion (partial pressure gradient) is diminished, less oxygen moves across the membrane; therefore, diffusion decreases, rather than increases despite higher ventilation.

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