Effects of pulmonary flow heterogeneity on oxygen transport parameters in exercise.

Under resting normoxic conditions, the healthy lung has ample oxygen uptake capacity relative to oxygen demand, but during exercise, increased oxygen demand and utilization become increasingly dependent on ventilation-perfusion matching. A mathematical model is used to investigate the effect of pulmonary flow heterogeneity, as characterized by the coefficient of variation (CV) of capillary blood flow, on pulmonary oxygen uptake in exercise. The model reveals that any level of heterogeneity up to a CV of 3 is consistent with the observed level of arterial oxygen tension under resting conditions, but that such high levels of heterogeneity are incompatible with the levels of oxygen uptake observed during exercise. If a normal diffusing capacity is assumed, the best fit to literature data on arterial oxygen content of exercising humans under normoxic and hypoxic conditions is found with a relatively low CV of 0.48, suggesting that local flow regulation mechanisms such as hypoxic pulmonary vasoconstriction play an important role in ventilation-perfusion matching during exercise.