On maximal oxygen consumption in hypoxic humans

Summary

The present paper discusses the factors affecting maximal O₂ consumption$\left( {\dot V_{O_2 } \max } \right)$ in hypoxia (4300 m above sea level) along the following lines: 1) In acute hypoxia, the fractional limitation to$\dot V_{O_2 } \max$ imposed by circulatory O₂ transport (FQ′) is 50%, instead of 70% as in normoxia. This is due to the increase in the blood O₂ transport coefficient (βb) as$P_{O_2 }$ decreases, as a consequence of the sigmoidal shape of the O₂ dissociation curve of hemoglobin. The remaining 50% is assumed to be equally partitioned between tissue O₂ transfer (Ft′) and mitochondria O₂ utilization (Fm′). 2) In chronic hypoxia, FQ′=0.45, Ft′=0.20 and Fm′=0.35, as a consequence of reduced muscle fiber size and muscle mitochondrial density following acclimatization. 3) The relationship between$\dot V_{O_2 } \max$ and$PI_{O_2 }$ in both acute and chronic hypoxia reflects the O₂ dissociation curve. 4) Acclimatization to chronic hypoxia does not have the function of preserving$\dot V_{O_2 } \max$.