Natural Acclimatization of Native Human Beings Living at High Altitudes
Many native human beings in the Andes and in the Himalayas live at altitudes above 13,000 feet—one group in the Peruvian Andes lives at an altitude of 17,500 feet and works a mine at an altitude of 19,000 feet. Many of these natives are born at these altitudes and live there all their lives. In all aspects of acclima-tization, the natives are superior to even the best-acclimatized lowlanders, even though the lowlanders might also have lived at high altitudes for 10 or more years. Acclimatization of the natives begins in infancy. The chest size, especially, is greatly increased, whereas the body size is somewhat decreased, giving a high ratio of ventilatory capacity to body mass. In addition, their hearts, which from birth onward pump extra amounts of cardiac output, are considerably larger than the hearts of lowlanders.
Delivery of oxygen by the blood to the tissues is also highly facilitated in these natives. For instance, Figure 43–2 shows oxygen-hemoglobin dissociation curves for natives who live at sea level and for their counterparts who live at 15,000 feet. Note that the arterial oxygen PO2 in the natives at high altitude is only 40 mm Hg, but because of the greater quantity of hemoglobin, the quantity of oxygen in their arterial blood is greater than that in the blood of the natives at the lower altitude. Note also that the venous PO2 in the high-altitude natives is only 15 mm Hg less than the venous PO2 for the lowlanders, despite the very low arterial PO2, indicating that oxygen transport to the tissues is exceedingly effective in the naturally acclimatized high-altitude natives.
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