Respiratory adaptation in the highest inhabitants and highest Sherpa mountaineers.

Arterial blood gases, acid-base and hematocrit of six highest inhabitants on Aucanquilcha (5950 m) in Chile were studied. These blood gases were compared with the alveolar gases of highest mountain climbers in Nepal, Sherpas and acclimatized lowlanders, and on average high altitude natives in the Chilean and Peruvian Andes and in the Nepal Himalayas. The mean arterial PCO2 (27.5 Torr) was lower than the standard sea level normal values, indicating a modest hypoxic hyperventilation. The mean arterial pH was 7.400, showing a complete renal compensation of respiratory alkalosis. The mean hematocrit (62%) and hemoglobin (20.7 g/dl) values were greater than the standard sea level values. These blood data showed that the highest inhabitants were acclimatized to hypoxia of their residential altitude. The respiratory gases showed less hyperventilation in the highest inhabitants and Sherpa mountaineers of high altitudes relative to the acclimatized lowlanders. Also, the average high altitude natives in the Andes and Himalayas showed less hyperventilation compared to the acclimatized lowlanders. We conclude that the attenuated hyperventilation is an appropriate respiratory adaptation to high altitude hypoxia in the native high altitude residents, allowing them to conserve metabolic energy expended for hyperventilation and to use the ventilatory reserve for a better performance at greater altitudes.