Similar peak VO2 at altitude in native lowland (Han Chinese) and Tibetan highland inhabitants despite different hemoglobin concentration [Hb

Abstract

Tibetan highlanders exhibit a unique suite of physiological traits, including markedly decreased [Hb] compared to Andean highlanders and high‐altitude sojourners at the same altitude. We performed exercise studies at 4200m in both native lowland Han Chinese males resident at >4000m for at least the past year (n = 7, [Hb]=19+/−0.77 g/dl) and native highland Tibetan males (n = 21, [Hb]=17.7+/−2.07 g/dl, p<0.02 between groups) to determine whether they differed in exercise capacity and/or one or more step(s) of the oxygen transport cascade. During maximal exercise we measured ventilation, VO2 and VCO2, heart rate, cardiac output, arterial PO2, PCO2, pH, HbP50, and arterial O2 saturation and calculated systemic O2 delivery and lung and muscle diffusional conductances (DL, DM). While peak VO2 and arterial blood gas variables were similar between groups, peak cardiac output and index trended lower in Han (both p < 0.11), which combined with higher [Hb], resulted in similar O2 delivery. DL normalized to lung volume trended higher (p < 0.07) in Tibetans, but DM was not different. These results show that in spite of lower [Hb], and thus O2 carrying capacity, Tibetan males can reach the same peak VO2 as Han, and appear to offset lower [Hb] by higher cardiac output, and possibly, lung diffusing capacity. How these differences relate to recently described changes in hypoxia‐sensitive genes in Tibetans remains to be determined.