Gilbert-Kawai, ET;
(2015)
Microcirculatory blood flow in hypoxia: a comparative study between Sherpas and Lowlanders.
Doctoral thesis , UCL (University College London).
Abstract
Sherpas are the direct descendants of nomadic Tibetans, a population known to have resided at altitude for well over 500 generations. As such, it is plausible that their genome has adapted, through natural selection, to cope with the surrounding hypobaric hypoxic environment. The resultant phenotypic changes, which could account for their anecdotal extraordinary hypoxic tolerance, remain poorly described. By comparing Sherpas and an altitude-naïve population - ‘Lowlanders’- this thesis attempts to investigate whether improved microcirculatory flow is a physiological mechanism utilised by indigenous high altitude native populations to aid successful adaptation (and thus tolerance) to hypoxia. Five studies were undertaken to assess the effects of acute, subacute, and sustained hypoxia on the microcirculation. In a normobaric hypoxic chamber study, Sherpas were seen to maintain significantly greater finger microcirculatory blood flow upon acute hypoxic exposure, as compared to Lowlanders. On ascent to Mount Everest Base Camp, Sherpas demonstrated greater resting sublingual, peripheral (finger) and forearm blood flow, in addition to increased sublingual capillary density. Lastly, when Lowlanders were exposed to sustained hypobaric hypoxia, their microcirculatory vessel density increased to levels indistinct from Sherpa values; however their microvascular blood flow remained significantly lower. The results from this thesis thus support the hypothesis that at the microcirculatory level, phenotypic differences exist between an indigenous high- altitude population and an altitude-naïve population. Accordingly, the findings sustain the notion that augmentation of oxygen delivery at the level of the microcirculation may be one physiological mechanism, sanctioned through evolutionary selection pressure, to aid successful adaptation to hypoxia.
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