Incorporating O/sub 2/-Hb reaction kinetics and the Fahraeus effect into a microcirculatory O/sub 2/-CO/sub 2/ transport model

The influence of O ₂-Hb reaction kinetics and the Fahraeus effect on steady state O ₂ and CO ₂ transport in cat brain microcirculation was investigated using the authors´ refined multicompartmental model. The most important model predictions include: (1) capillaries are the sites in the microcirculation where the effect of O ₂-Hb kinetics is most pronounced; (2) while there is only a small difference between equilibrium and actual oxygen saturation, this effect is not negligible; (3) O ₂-Hb kinetics tends to make the PO ₂ level at the venous entrance higher than in venules; (4) the influence of the Fahraeus effect leads to a lower tissue PO ₂ level than in venules and the outlet vein. The resultant decline in tissue PO ₂ may lead to a decrease in O ₂ consumption rate and extraction ratio; (5) although the Fahraeus effect changes the ratio between arteriolar flux and capillary flux, incorporating the Fahraeus effect and O ₂-Hb kinetics into the simulation does not change the authors´ previous conclusion that most of the O ₂ and CO ₂ exchange takes place at the capillary level; (6) in general, influences of O ₂-Nb kinetics and Fahraeus effect are synergistic; (7) a model that excludes these two mechanisms might overestimate the tissue oxygenation level especially during severe hypoxia.