Rate of ventilatory acclimatization to extreme altitude

One of the most important factors in the acclimatization of lowlanders to high altitude is hyperventilation which helps to defend the alveolar PO2. However, how rapidly this occurs at very high altitude is poorly understood. Information can be obtained by comparing the alveolar gas values reported from the extended low pressure chamber studies, Operation Everest I and II, and the American medical research expedition to Everest (AMREE) of 1981. Rahn and Otis (1949) reported the alveolar PO2 and PCO2 values for non-acclimatized and well-acclimatized man on an O2-CO2 diagram, and pointed out that the Operation Everest I data fell approximately halfway between the two curves. The AMREE data agree well with the fully-acclimatized curve, and the Operation Everest II values are intermediate. The differences can be partly, though not wholly, attributed to the different periods of acclimatization. The conclusion is that 31 and 36 days are inadequate periods of acclimatization for altitudes over 8000 m, but that 77 days is sufficient. However, other factors are also involved.