O-2-HB REACTION-KINETICS AND THE FAHRAEUS EFFECT DURING STAGNANT, HYPOXIC, AND ANEMIC SUPPLY DEFICIT

We modified our previous computer model of O-2 and CO2 transport in th e cerebral microcirculation to include nonequilibrium O-2-Hb kinetics and the Fahraeus effect (reduced tube hematocrit in small microvessels ). The model is a steady-state multicompartmental simulation which inc ludes three arteriolar compartments, three venular compartments, and o ne capillary compartment. Three different types of oxygen deficits (st agnant, hypoxic, and anemic conditions) were simulated by respectively reducing blood flow, arterial O-2 saturation, and systemic hematocrit to one half of normal. Microcirculatory distributions for P-O2, P-CO2 , O-2 saturation and deviations from equilibrium, and the O-2 and CO2 fluxes for each compartment were predicted for the three O-2 supply de ficits. Differences were found for O-2 extraction ratios and relative contributions of arteriolar, venular, and capillary gas fluxes for eac h type of deficit. The Fahraeus effect and O-2-Hb kinetics reduced O-2 extraction in all cases and altered microcirculatory gas distribution s depending on the specific type of O-2 supply deficits. The modified model continues to predict that capillaries are the major site where g as exchange takes place, and demonstrates that the Fahraeus effect and nonequilibrium O-2-Hb kinetics are important mechanisms that should n ot be neglected in O-2 and CO2 transport modeling. While this model pr ovides useful insight regarding the influence of the Fahraeus effect a nd O-2-Hb kinetics under steady state, the addition of a distributed a nd dynamic simulation should further elucidate the effects of the brai n's heterogeneous properties and transient behavior. (C) 1998 Biomedic al Engineering Society. [S0090-6964(98)00401-9].