Theoretical predictions of maximal oxygen consumption in hypoxia: effects of transport limitations

A Krogh-type model for oxygen transport is used to predict maximal oxygen consumption ((V)over dotO(2max)) of human skeletal muscle under hypoxic conditions. Assumed values of capillary density, blood flow, and hemoglobin concentration are based on measurements undernormoxic and hypoxic exercise conditions. Arterial partial pressure of oxygen is assumed to decrease with reductions in inspired partial pressure of oxygen (P1O2), as observed experimentally. As a result of limitations of convective and diffusive oxygen delivery, predicted (V)over dotO(2max) values decline gradually as P1O2 is reduced from 150 mmHg to about 80 mmHg, and more rapidly as P1O2 is further reduced. At very low levels of P1O2, (V)over dot(2max) is limited primarily by convective oxygen supply. Experimentally observed values of (V)over dotO(2max) in hypoxia show significant dispersion, with some values close to predicted levels and others substantially lower. These results suggest that maximal oxygen consumption rates in hypoxia are not necessarily determined by oxygen transport limitations and may instead reflect reduced muscle oxygen demand. (C) 2004 Elsevier B.V. All rights reserved.