Tibetans Retained Innate Ability Resistance to Acute Hypoxia after Long Period of Residing at Sea Level

Abstract

Could the intrinsic characteristics of tolerance to hypoxia be retained in Tibetan high-altitude natives after they had migrated to a low altitude? To answer this question, we undertook a study of 33 healthy male adolescent Tibetans born and raised in a high plateau (3,700 m [12,140 ft] above sea level) who migrated to Shanghai (sea level) for 4 years. Ten age-matched healthy male Han adolescents born and raised in Shanghai were regarded as the control group. Acute hypoxia was induced in a hypobaric chamber for 2 h to simulate the 3,700 m altitude. At sea level, maximal oxygen consumption (VO_{2 max}) was not significantly different between the two groups. During acute hypoxia, the values of VO_{2 max}, tissue oxygen extraction, arterial oxygen pressure, and the arterial oxygen saturation showed markedly higher in Tibetan subjects than in Han subjects (1.41 ± 0.04 l/min/M² vs.1.25 ± 0.04 l/min/M², 55.0 ± 4.2% vs. 47.3 ± 9.1%, 7.2 ± 0.6 vs. 5.5 ± 0.2 kPa, and 87.9 ± 3.3% vs. 78.2 ± 1.6%, respectively, P < 0.05). The calculated “oxygen reserve capacity” and “cardiac reserve capacity” were better in the Tibetans than in the Han natives (P < 0.05), which suggests that physical work capacity is greater in the Tibetan group. The sympathetic stimulation was less, and there was no noticeable change in cardiac function during acute hypoxia in the Tibetan group. The results indicate that the better tolerance to hypoxia in the Tibetans is retained during the 4-year stay at sea level, implying that the intrinsic hypoxic adaptation still exists in the Tibetan high-altitude natives.