THE EFFECT OF BLOOD-FLOW ON OXYGEN EXTRACTION PRESSURES CALCULATED INA MODEL OF POINT-LIKE ERYTHROCYTE SOURCES FOR RAT-HEART

A mathematical description of pericapillary oxygen gradients that take s into account the particulate nature of blood is possible in terms of erythrocytes as pointlike sources. The formulation in terms of quasi- stationary sources [1] is extended to account for moving erythrocytes. The extended model is semianalytical and can be used to estimate the extraction pressure (EP), which quantifies the effect on partial press ure of oxygen (pO(2)) in the tissue far from the erythrocytes. Simulat ions have been done for rat heart muscle tissue around a capillary. Fo r low hematocrit (Hct; 20%) and low blood velocity EP is highest, high er than the pO, drop in a surrounding typical tissue cylinder. This me ans that the impediment to O-2 release close to the capillary can be l arger than that to transport further into the tissue. Increasing the h ematocrit decreases EP, that is, it facilitates O-2 release. Increasin g the blood velocity decreases EP at low Hct values but has the opposi te effect at high Hct values (> 35%). For zero velocity, results are t he same as with the quasi-stationary model.