VENTILATION AND HYPOXIC VENTILATORY RESPONSE OF TIBETAN AND AYMARA HIGH-ALTITUDE NATIVES

Newcomers acclimatizing to high altitude and adult male Tibetan high a ltitude natives have increased ventilation relative to sea level nativ es at sea level. However, Andean and Rocky Mountain high altitude nati ves have an intermediate level of ventilation lower than that of newco mers and Tibetan high altitude natives although generally higher than that of sea level natives at sea level. Because the reason for the rel ative hypoventilation of some high altitude native populations was unk nown, a study was designed to describe ventilation from adolescence th rough old age in samples of Tibetan and Andean high altitude natives a nd to estimate the relative genetic and environmental influences. This paper compares resting ventilation and hypoxic ventilatory response ( HVR) of 320 Tibetans 9-82 years of age and 542 Bolivian Aymara 13-94 y ears of age, native residents at 3,800-4,065 m. Tibetan resting ventil ation was roughly 1.5 times higher and Tibetan HVR was roughly double that of Aymara. Greater duration of hypoxia (older age) was not an imp ortant source of variation in resting ventilation or HVR in either sam ple. That is, contrary to previous studies, neither sample acquired hy poventilation in the age ranges under study. Within populations, great er severity of hypoxia (lower percent of oxygen saturation of arterial hemoglobin) was associated with slightly higher resting ventilation a mong Tibetans and lower resting ventilation and HVR among Aymara women , although the associations accounted for just 2-7% of the variation. Between populations, the Tibetan sample was more hypoxic and had highe r resting ventilation and HVR. Other systematic environmental contrast s did not appear to elevate Tibetan or depress Aymara ventilation. The re was more intrapopulation genetic variation in these traits in the T ibetan than the Aymara sample. Thirty-five percent of the Tibetan, but none of the Aymara, resting ventilation variance was due to genetic d ifferences among individuals. Thirty-one percent of the Tibetan HVR, b ut just 21% of the Aymara, HVR variance was due to genetic differences among individuals. Thus there is greater potential for evolutionary c hange in these traits in the Tibetans. Presently, there are two differ ent ventilation phenotypes among high altitude natives as compared wit h sea level populations at sea level: lifelong sustained high resting ventilation and a moderate HVR among Tibetans in contrast with a sligh tly elevated resting ventilation and a low HVR among Aymara. (C) 1997 Wiley-Liss, Inc.