Pii: S0025-5564(00)00038-9

Characterizing the resistances to O2 transport from the erythrocyte to the mitochondrion is important to understanding potential transport limitations. A mathematical model is developed to accurately determine the e€ects of erythrocyte spacing (hematocrit), velocity, and capillary radius on the mass transfer coecient. Parameters of the hamster cheek pouch retractor muscle are used in the calculations, since signi®cant amounts of experimental physiological data and mathematical modeling are available for this muscle. Capillary hematocrit was found to have a large e€ect on the PO2 distribution and the intracapillary mass transfer coecient per unit capillary area, kcap, increased by a factor of 3.7 from the lowest (H ˆ 0:25) to the highest (H ˆ 0:55) capillary hematocrits considered. Erythrocyte velocity had a relatively minor e€ect, with only a 2.7% increase in the mass transfer coecient as the velocity was increased from 5 to 25 times the observed velocity in resting muscle. The capillary radius is varied by up to two standard deviations of the experimental measurements, resulting in variations in kcap that are <15% at the reference case. The magnitude of these changes increases with hematocrit. An equation to approximate the dependence of the mass transfer coecient on hematocrit is developed for use in simulations of O2 transport from a capillary network. Ó 2000 Elsevier Science Inc. All rights reserved.