At high altitudes, atmospheric pressure is reduced from 760 mm Hg of sea level. Because atmospheric pressure is a factor that determines room air and alveolar PO2 (oxygen pressure), these two values are also reduced. These two values are permanently depressed unless enriched oxygen is inspired.
Therefore,PAO2 < 100 mm Hg, PaO2 < 100 mm Hg and low arterial PO2 will stimulate the peripheral chemo-receptors and increase alveolar ventilation.
At high altitude, then, the main drive for ventilation changes from CO2 on the central chemo-receptors at sea level to a low PO2 drive of the peripheral chemo-receptors and hyperventilation ensues.
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