Second generation Tibetan lowlanders acclimatize to high altitude more quickly than Caucasians

As is well known, with increasing altitude, peak aerobic power (VO2peak) of acclimatized lowlanders undergoes a progressive decrease as a consequence of the decline of barometric pressure and of oxygen partial pressure in inspired air. At any given altitude, however, the percentage reduction of VO2peak compared to sea level control values (ΔVO2peak,%) varies widely among individuals (Cerretelli & Hoppeler, 1996). Such variability appears to be mainly related to the extent of acclimatization and to the degree of fitness. A prolonged sojourn at very high altitude (>5500 m) may affect VO2peak of lowlanders both positively, by the increase of blood O2 carrying capacity (Grassi et al. 1996) and negatively, as a consequence of a progressive reduction of muscle mass (Cerretelli, 1976) and, possibly, of muscle deterioration (Martinelli et al. 1990). If the duration of the exposure is long enough (years) and altitude does not exceed ∼4000 m, developmental adaptation may occur (Moore, 2001) allowing a progressive recovery of the VO2peak towards levels only slightly lower than those found at sea level in age-, fitness- or training-matched individuals (Frisancho et al. 1973; Greska et al. 1985; Sun et al. 1990; Niu et al. 1995; Chen et al. 1997). With regard to fitness, in acute hypoxia, the peak aerobic power reduction was found to be greater in physically active than in inactive Caucasians (Lawler et al. 1988; Shephard et al. 1988; Martin & O'Kroy, 1993; Koistinen et al. 1995) as a consequence, among others, of a greater lung diffusion limitation (Dempsey et al. 1984; Dempsey & Wagner, 1999). Also in subchronic (Young et al. 1985) and chronic (Marzorati et al. 1995) hypoxia, there are hints that trained individuals may be more penalized in terms of ΔVO2peak than untrained subjects. Compared to acclimatized lowlanders and even Andean populations, altitude Tibetans exhibit at peak exercise peculiar adaptive features, such as higher arterial O2 saturation (Zhuang et al. 1996) and heart rate values (Niu et al. 1995), and absolute VO2peak levels (Sun et al. 1990; Niu et al. 1995; Chen et al. 1997) close to those found in Caucasians at sea level. These findings, along with a less pronounced polycythemic response (Beall et al. 1998), a reduced hypoxic pulmonary vasoconstriction (Groves et al. 1993), and a lower prevalence of chronic mountain sickness (Moore et al. 1998), suggest that in altitude Tibetans the pattern of adaptation to chronic hypoxia is different compared to that of any other population. The present study was designed primarily to establish whether resistance to hypoxia and, particularly the greater aerobic working capacity found in altitude Tibetans has a genetic basis. Should this be the case, Tibetan lowlanders born with the genetic adaptations of their ancestors, i.e. long-term processes occurring over generations (Moore, 2001), could be expected to acclimatize to high altitude more quickly than Caucasians. As an additional aim, we investigated the role of aerobic fitness, independent of ethnicity, on the preservation of peak aerobic performance at altitude. To achieve these aims, the respiratory and cardiovascular responses to peak exercise, particularly the altitude-induced decrease of VO2peak (ΔVO2peak) were assessed in Tibetans with different altitude exposure history and in Caucasian lowlanders with different levels of aerobic fitness, following an identical (26–28 days) altitude (5050 m) exposure protocol.