Higher arterial oxygen saturation during submaximal exercise in Bolivian Aymara compared to European sojourners and Europeans born and raised at high altitude

Abstract

Arterial oxygen saturation (SaO(2)) was measured at 3,600-3,850 m by pulse oximetry at rest and during submaximal exercise in three study groups: 1) highland Aymara natives of the Bolivian altiplano (n = 25); 2) lowland European/North American sojourners to the highlands with at least 2 months of acclimatization time to 3,600 m (n = 27); and 3) subjects of European ancestry born and raised at 3,600 m (n = 22). Aymara subjects maintained approximately 1 percentage point higher SaO(2) during submaximal work up to 70% of their maximal work capacity, and showed a smaller rate of decline in SaO(2) with increasing work compared to both European study groups. The higher-exercise SaO(2) of Aymara compared to Europeans born and raised at 3,600 m suggests genetic adaptation. The two European study groups, who differed by exposure to high altitude during their growth and development period, did not show any significant difference in either resting or exercise SaO(2). This suggests that the developmental mode of adaptation is less important than the genetic mode of adaptation in determining exercise SaO(2). A weak correlation was detected (across study groups only) between the residual forced vital capacity (FVC) and the residual SaO(2) measured at the highest level of submaximal work output (P = 0.024, R = 0.26). While firm conclusions based on this correlation are problematic, it is suggested that a part of the higher SaO(2) observed in Aymara natives is due to a larger lung volume and pulmonary diffusion capacity for oxygen. Results from this study are compared to similar studies conducted with Tibetan natives, and are interpreted in light of recent quantitative genetic analyses conducted in both the Andes and Himalayas.

Human high-altitude adaptation: forward genetics meets the HIF pathway

“…When measured at high altitude, individuals of low-altitude ancestry who are born and raised at high altitude do not exhibit differences in their SaO 2 levels compared with individuals of low-altitude ancestry who are born and raised at low altitude (Dempsey et al 1971;Frisancho et al 1995). For example, European sojourners to high altitude exhibit similar SaO 2 values compared with Europeans born and raised at high altitude (Brutsaert et al 2000), thus suggesting that there are no developmental effects of chronic hypoxia exposure on SaO 2 . Among long-term residents of high altitude, Andean highlanders display arterial oxygen levels that are ;16% higher than sea-level inhabitants residing at high altitude (Beall 2006).…”

“…Among long-term residents of high altitude, Andean highlanders display arterial oxygen levels that are ;16% higher than sea-level inhabitants residing at high altitude (Beall 2006). This is due in part to their increased SaO 2 levels, where Andeans maintain higher levels of SaO 2 at rest and during exercise compared with sea-level inhabitants measured at the same altitude (Brutsaert et al 2000). Tibetan highlanders also exhibit higher levels of SaO 2 compared with low-altitude residents measured at the same altitude (Wu and Kayser 2006), but their average SaO 2 levels at rest are not significantly different from Han Chinese born and raised at high-altitude and are lower than those observed among Andeans when measured using the same equipment and protocol (Beall et al 1997b(Beall et al , 1999Weitz and Garruto 2007).…”

“…Among indigenous high-altitude populations, two distinct pulmonary responses to continued hypoxia exposure have been observed. Andeans exhibit no increase in resting ventilation levels over low-altitude values at rest or during exercise (Chiodi 1957;Brutsaert et al 2000) and a blunted HVR (Chiodi 1957;Beall et al 1997a) that is commonly lower than sea-level values. Pointing to a genetic basis for this trait, the Andean HVR has been associated with Quechua ancestry (Brutsaert et al 2005), thus suggesting an evolutionary origin.…”

Ancestry explains the blunted ventilatory response to sustained hypoxia and lower exercise ventilation of Quechua altitude natives

“…3) and VE/V O 2 (P ϭ 0.013) measured at altitude compared with subjects with relatively high EAP (Ͼ0.35) and low NAAP (Ͻ0.65). Thus Quechua ancestry may be partly responsible for the well-known blunted HVR (10,35,36,57,62) and the relative exercise hypoventilation at altitude (7,32,55,66) of Andeans compared with European controls. From the novel study design, we infer both a population genetic basis and an evolutionary origin for these trait differences.…”

“…The sustained vs. acute response has not been systematically evaluated in Andean highland natives, but groups from this region appear to have a lower or "blunted" acute HVR and a lower effective alveolar ventilation compared with high altitude (HA)-acclimatized control groups from the lowlands (10,35,36,43,57,61,62). Andeans also have lower VE during exercise at HA compared with acclimatized lowland controls (7,32,55,66). These traits may be unique to Andeans, as many studies show normal HVR and higher VE in natives of the Himalayan plateau (2,21,25,29,75).…”