Parametric analysis of the relationship between end-capillary and mean tissue PO2 as predicted by a mathematical model

An increase of the partial pressure of oxygen in venules towards larger ves sels has been observed experimentally, but the mechanism of this phenomenon has not been established. The present study considers a simple mathematica l model of oxygen transport from a capillary to the surrounding tissue cyli nder and analyses the conditions under which the end-capillary partial pres sure of oxygen is lower that the mean tissue pressure. Under these conditio ns oxygen would diffuse into the venules since they are surrounded by the t issue with a higher partial pressure of oxygen. Cerebral circulation is cho sen for these calculations and conditions of normoxia, hypoxic hypoxia, car bon monoxide hypoxia, anemia, and polycythemia are simulated. The tissue me tabolic rate is also varied. It is found that under most conditions the rel ationship between the end-capillary and mean tissue partial pressures of ox ygen can be reversed when one of the parameters is varied within its physio logical range, i.e. the difference between these variables could be either positive or negative depending on the value of the parameters. Therefore, u nder many realistic conditions this mechanism would contribute to an increa se of the partial pressure of oxygen in the venules. This conclusion should hold for a more realistic geometrical model of capillary network, but the relationships between the end-capillary and mean tissue partial pressures o f oxygen, in addition to their dependence on the parameters considered in t his study, would likely be dependent on the spatial location within the net work. (C) 1998 Academic Press.