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If a competition between the oxygen demands of limb and respiratory muscles happens, hypoxia may favor redistribution of blood flow from peripheral to respiratory muscles during heavy exercise. This hypothesis was tested in eighteen lowlanders and 27 highlanders at 4350m altitude. During an incremental exercise, the regional tissue oxygen saturation (rSO2) and tissue hemoglobin concentration ([Hbt]) of the intercostal muscles and vastus medialis were monitored simultaneously by NIRS. The intercostal and vastus medialis rSO2 values were lower at altitude than at sea level (-10%, p<0.001) and decreased similarly during incremental exercise (p<0.001) while [Hbt] values increased. At maximal exercise, the intercostal rSO2 was lower than the vastus medialis rSO2 in lowlanders (-7%, p<0.001). In highlanders the time patterns were similar but intercostal rSO2 was less decreased at exercise (p<0.05). Maximal exercise performed in hypoxia did not alter the kinetics of rSO2 and [Hbt] in peripheral muscles. These findings do not favor the hypothesis of blood flow redistribution., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Tibetans have been reported to present with a unique phenotypic adaptation to high altitude characterized by higher resting ventilation and arterial oxygen saturation, no excessive polycythemia, and lower pulmonary arterial pressures (Ppa) compared with other high-altitude populations. How this affects exercise capacity is not exactly known. We measured aerobic exercise capacity during an incremental cardiopulmonary exercise test, lung diffusing capacity for carbon monoxide (DL(CO)) and nitric oxide (DL(NO)) at rest, and mean Ppa (mPpa) and cardiac output by echocardiography at rest and at exercise in 13 Sherpas and in 13 acclimatized lowlander controls at the altitude of 5,050 m in Nepal. In Sherpas vs. lowlanders, arterial oxygen saturation was 86 ± 1 vs. 83 ± 2% (mean ± SE; P = nonsignificant), mPpa at rest 19 ± 1 vs. 23 ± 1 mmHg (P < 0.05), DL(CO) corrected for hemoglobin 61 ± 4 vs. 37 ± 2 ml · min(-1) · mmHg(-1) (P < 0.001), DL(NO) 226 ± 18 vs. 153 ± 9 ml · min(-1) · mmHg(-1) (P < 0.001), maximum oxygen uptake 32 ± 3 vs. 28 ± 1 ml · kg(-1) · min(-1) (P = nonsignificant), and ventilatory equivalent for carbon dioxide at anaerobic threshold 40 ± 2 vs. 48 ± 2 (P < 0.001). Maximum oxygen uptake was correlated directly to DL(CO) and inversely to the slope of mPpa-cardiac index relationships in both Sherpas and acclimatized lowlanders. We conclude that Sherpas compared with acclimatized lowlanders have an unremarkable aerobic exercise capacity, but with less pronounced pulmonary hypertension, lower ventilatory responses, and higher lung diffusing capacity.