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

Abstract

Tibetan highlanders develop at altitude peak aerobic power levels close to those of Caucasians at sea level. In order to establish whether this feature is genetic and, as a consequence, retained by Tibetan lowlanders, altitude-induced changes of peak aerobic performance were assessed in four groups of volunteers with different ethnic, altitude exposure and fitness characteristics, i.e. eight untrained second-generation Tibetans (Tib 2) born and living at 1300 m; seven altitude Sherpas living at approximately 2800-3500 m; and 10 untrained and five trained Caucasians. Measurements were carried out at sea level or at Kathmandu (1300 m, Nepal) (PRE), and after 2-4 (ALT1), 14-16 (ALT2), and 26-28 (ALT3) days at 5050 m. At ALT3, of untrained and trained Caucasians was -31% and -46%, respectively. By contrast, of Tib 2 and Sherpas was -8% and -15%, respectively. At ALT3, peak heart rate (HR(peak)) of untrained and trained Caucasians was 148 +/- 11 and 149 +/- 7 beats min(-1), respectively; blood oxygen saturation at peak exercise was 76 +/- 6% and 73 +/- 6%, and haemoglobin concentration ([Hb]) was 19.4 +/- 1.0 and 18.6 +/- 1.2 g dl(-1), respectively. Compared to Caucasians, Tib 2 and Sherpas exhibited at ALT3 higher HR(peak) (179 +/- 9 and 171 +/- 4 beats min(-1), P < 0.001), lower [Hb] (16.6 +/- 0.6 and 17.4 +/- 0.9 g dl(-1), respectively, P < 0.001), and slightly but non-significantly greater average values (82 +/- 6 and 80 +/- 7%). The above findings and the time course of adjustment of the investigated variables suggest that Tibetan lowlanders acclimatize to chronic hypoxia more quickly than Caucasians, independent of the degree of fitness of the latter.

Figure 1. Altitude profile and the sequence of testing sessions for untrained (UT) and trained (T) Caucasians, and for Tibetan lowlanders (Tib 2) and Sherpas (Sh)

Untrained and trained Caucasians underwent control measurements (PRE) at sea level. The same data were adopted also at 1300 m, based on the observation that V̇_O2peak of sedentary subjects is not affected by altitudes below 1500 m (Terrados et al. 1985; Gore et al. 1996). Control measurements (PRE) in Tibetan lowlanders were performed at 1300 m. Experiments were carried out 2–4 (ALT1), 14–16 (ALT2), and 26–28 (ALT3) days after arrival at the Pyramid-Laboratory. At ALT3, Tibetan lowlanders repeated the test also in acute hypobaric normoxia (ALT3-O₂). At altitude, Sherpas underwent experiments only on one occasion (ALT3) and thereafter they were brought and tested at 1300 m (PRE).

Figure 2. Time course of the percentage change of peak oxygen consumption expressed per kg of body mass (Δ V̇_O2peak, the PRE value made equal to 0) of Tibetan lowlanders, Sherpas, and untrained and trained Caucasians during the sojourn at 5050 m

*P < 0.05 when comparing Caucasians with Tibetans and Sherpas at a given condition. †,‡P < 0.05 when comparing ALT3 with ALT1 and ALT2, respectively.

Figure 3. Individual loss of peak aerobic power expressed per kg of body mass (Δ V̇_{O2peak, %})after 26–28 days (ALT3) at 5050 m, as a function of the corresponding PRE peak aerobic power (V̇_O2peak, ml kg⁻ min⁻)

Mean values ±s.d. of the 4 groups of subjects are also shown (large symbols). Continuous lines (A and B), fitted through individual values, differ significantly from each other (P < 0.05).

Figure 4. Individual loss of peak aerobic power expressed per kg of body mass (Δ V̇_O2peak,%) after 26–28 days (ALT3) at 5050 m, as a function of the corresponding value of arterial O₂ saturation (S_aO2peak,%) at peak exercise

Regression equations were determined for untrained and trained Caucasians (A′, P < 0.01) and for Tibetan lowlanders and Sherpas (B′, P < 0.01). The difference between the two equations is statistically significant (P < 0.01).