Estimating oxygen transport resistance of the microvascular wall

The problem of diffusion of O₂ across the endothelial surface in precapillary vessels and its utilization in the vascular wall remains unresolved. To establish a relationship between precapillary release of O₂ and vascular wall consumption, we estimated the intravascular flux of O₂ on the basis of published in vivo measurements. To interpret the data, we utilized a diffusion model of the vascular wall and computed possible physiological ranges for O₂ consumption. We found that many flux values were not consistent with the diffusion model. We estimated the mitochondrial-based maximum O₂ consumption of the vascular wall (M(mt)) and a possible contribution to O₂ consumption of nitric oxide production by endothelial cells (M(NO)). Many values of O₂ consumption predicted from the diffusion model exceeded M(mt) + M(NO). In contrast, reported values of O₂ consumption for endothelial and smooth muscle cell suspensions and vascular strips in vitro do not exceed M(mt). We conjecture that most of the reported values of intravascular O₂ flux are overestimated, and the likely source is in the experimental estimates of convective O₂ transport at upstream and downstream points of unbranched vascular segments.