Calculations of intracapillary oxygen tension distributions in muscle

Characterizing the resistances to O-2 transport from the erythrocyte to the mitochondrion is important to understanding potential transport limitation s. A mathematical model is developed to accurately determine the effects of erythrocyte spacing (hematocrit), velocity, and capillary radius on the ma ss transfer coefficient. Parameters of the hamster cheek pouch retractor mu scle are used in the calculations, since significant amounts of experimenta l physiological data and mathematical modeling are available for this muscl e. Capillary hematocrit was found to have a large effect on the PO2 distrib ution and the intracapillary mass transfer coefficient per unit capillary a rea, k(cap), increased by a factor of 3.7 from the lowest (H = 0.25) to the highest (H = 0.55) capillary hematocrits considered. Erythrocyte velocity had a relatively minor effect, with only a 2.7% increase in the mass transf er coefficient as the velocity was increased from 5 to 25 times the observe d velocity in resting muscle. The capillary radius is varied by up to two s tandard deviations of the experimental measurements, resulting in variation s in k(cap) that are <15% at the reference case. The magnitude of these cha nges increases with hematocrit. An equation to approximate the dependence o f the mass transfer coefficient on hematocrit is developed for use in simul ations of O-2 transport from a capillary network. (C) 2000 Elsevier Science Inc. All rights reserved.