Hypoxic ventilatory responsiveness in Tibetan compared with Han residents of 3,658 m

Abstract

Lifelong high-altitude residents of North and South America acquire blunted hypoxic ventilatory responses and exhibit decreased ventilation compared with acclimatized newcomers. The ventilatory characteristics of Himalayan high-altitude residents are of interest in the light of their reportedly lower hemoglobin levels and legendary exercise performance. Until recently, Sherpas have been the only Himalayan population available for study. To determine whether Tibetans exhibited levels of ventilation and hypoxic ventilatory drives that were as great as acclimatized newcomers, we compared 27 lifelong Tibetan residents of Lhasa, Tibet, China (3,658 m) with 30 acclimatized Han ("Chinese") newcomers matched for age, body size, and extent of exercise training. During room air breathing, minute ventilation was greater in the Tibetan than in the Han young men because of an increased respiratory frequency, but arterial O2 saturation and end-tidal PCO2 did not differ, indicating similar levels of effective alveolar ventilation. The Tibetan subjects had higher hypoxic ventilatory response shape parameter A values and hypercapnic ventilatory responsiveness than the Han subjects. Among the Han subjects, duration of high-altitude residence correlated with the degree of blunting of the hypoxic ventilatory drive. Paradoxically, hyperoxia (inspired O2 fraction 0.70) increased minute ventilation and decreased end-tidal PCO2 in the Tibetan but not in the Han men. We concluded that lifelong Tibetan residents of high altitude neither hypoventilated nor exhibited blunted hypoxic ventilatory responses compared with acclimatized Han newcomers, suggesting that the effects of lifelong high-altitude residence on ventilation and ventilatory response to hypoxia differ in Tibetan compared with other high-altitude populations.

Neonatal Oxygenation, Pulmonary Hypertension, and Evolutionary Adaptation to High Altitude (2013 Grover Conference series)

“…75 This may be a body-wide response, since greater lower-limb vasodilator response to ischemia 76 and greater forearm blood flow in association with higher circulating NO products 77 have been observed in Sherpa or Tibetans than in sea-level residents of the United States or acclimatized lowlanders. Population differences in ventilatory sensitivity to hypoxia and hence arterial oxygenation are also likely involved, since Tibetans resemble acclimatized lowlanders by having a brisk ventilatory response to hypoxia, higher levels of alveolar ventilation, 78 and higher SaO 2 in most, but not all, studies (see Gilbert-Kawai et al 79 for a recent review).…”

Angiotensin converting enzyme insertion allele in relation to high altitude adaptation

“…Variations in the observed characteristics may reflect differences in adaptive response to hypobaric hypoxia (Zhuang et al 1993 ;Heath & Williams, 1995). A correlation could not be observed between the genotype and the characteristics (Table 1) ; however, it seemed that body weight and BMI increased with the D allele, which was comparatively greater in number in the LLs, followed by the HLs and MLLs.…”

Natural selection on EPAS1 ( HIF2α ) associated with low hemoglobin concentration in Tibetan highlanders

“…Typically, Tibetans average at least 1 g/dL and as much as approximately 3.5 gm/dL (i.e. approximately 10-20%) lower hemoglobin concentration in comparison with their Andean counterparts (14)(15)(16) or acclimatized lowlanders, such as the Han who have moved to altitudes above 2,500 m (4,(17)(18)(19)(20)(21)(22)(23). This suggests that Tibetans have evolved a blunted erythropoietic response to high-altitude hypoxia.…”