Heterogeneity of oxygen delivery impairs oxygen extraction by peripheral tissues: theory

The hypothesis that the distribution of oxygen demand in relation to oxygen supply (dO2/qO2) effects oxygen extraction in peripheral tissues was tested. By using a simple theoretical model, realistic biphasic oxygen consumption-delivery relationships were predicted from dO2/qO2 distributions. Increasing width (relative dispersion) of the dO2/qO2 distribution, indicating mismatch between oxygen demand and supply, nonlinearly decreased the critical oxygen extraction ratio (calculated by using dual-line regression). Skewed dO2/qO2 distributions had a lesser effect. Incomplete oxygen uptake, due to diffusion limitation or other causes of physiological arteriovenous shunt, linearly decreased the critical oxygen extraction ratio. Approximate dO2/qO2 distributions were then estimated from previously reported capillary transit-time distributions. Critical oxygen extraction ratios predicted from these estimated dO2/qO2 distributions match reported values. This theoretical approach also predicts the decrease in the critical oxygen extraction ratio in porcine gut after endotoxin infusion in the companion paper (M. F. Humer, P. T. Phang, B. P. Friesen, M. F. Allard, C. M. Goddard, and K. R. Walley. J. Appl. Physiol. 81: 895-904, 1996). Much as pulmonary ventilation-perfusion relationships account for pulmonary gas exchange, dO2/qO2 distributions quantitatively account for measured tissue oxygen extraction and predict novel features of the relationship between heterogeneity and oxygen extraction.