O₂–Hb Reaction Kinetics and the Fåhraeus Effect during Stagnant, Hypoxic, and Anemic Supply Deficit

Abstract

We modified our previous computer model of O2 and CO2 transport in the cerebral microcirculation to include nonequilibrium O2-Hb kinetics and the Fåhraeus effect (reduced tube hematocrit in small microvessels). The model is a steady-state multicompartmental simulation which includes three arteriolar compartments, three venular compartments, and one capillary compartment. Three different types of oxygen deficits (stagnant, hypoxic, and anemic conditions) were simulated by respectively reducing blood flow, arterial O2 saturation, and systemic hematocrit to one half of normal. Microcirculatory distributions for PO2, PCO2, O2 saturation and deviations from equilibrium, and the O2 and CO2 fluxes for each compartment were predicted for the three O2 supply deficits. Differences were found for O2 extraction ratios and relative contributions of arteriolar, venular, and capillary gas fluxes for each type of deficit. The Fåhraeus effect and O2-Hb kinetics reduced O2 extraction in all cases and altered microcirculatory gas distributions depending on the specific type of O2 supply deficits. The modified model continues to predict that capillaries are the major site where gas exchange takes place, and demonstrates that the Fåhraeus effect and nonequilibrium O2-Hb kinetics are important mechanisms that should not be neglected in O2 and CO2 transport modeling. While this model provides useful insight regarding the influence of the Fahraeus effect and O2-Hb kinetics under steady state, the addition of a distributed and dynamic simulation should further elucidate the effects of the brain's heterogeneous properties and transient behavior.

Impact of the Fåhraeus Effect on NO and O2 Biotransport: A Computer Model

“…We have previously shown that the Fåhraeus effect has an impact on O 2 transport modeling (52,53) and in this study we demonstrate that it is also important in NO transport modeling. Experimental data in the literature on the Fåhraeus effect were reviewed by Goldsmith et al (14).…”

“…There are other implications for coupled NO and O 2 transport that were not fully explored in our simulations. For example, we did not include the longitudinal decrease in intravascular blood P O 2 along vascular networks that has been predicted from our previous O 2 transport models (50)(51)(52)(53) and is observed experimentally, as reviewed by Tsai et al (41). For example, intravascular blood P O 2 values determined by optical phosphorescence quenching in the smallest skinfold arterioles of conscious hamsters decrease to values in the 30-to 40-torr range, which is below the value of 50 torr used in the simulation for a 20-µm-diameter arteriole shown in Figure 5, and significantly below the value of 70 torr used in our simulations for larger arterioles (Figures 3, 4, 6).…”

Can We Model Nitric Oxide Biotransport? A Survey of Mathematical Models for a Simple Diatomic Molecule with Surprisingly Complex Biological Activities

“…Another factor is the well known Fähraeus-Lindqvist effect, in which the particulate nature of blood leads to a reduced hematocrit in small tubes. This can be less than half of the systemic hematocrit in capillaries or small arterioles and venules (diameters ∼15 µm) and has significant effects in O 2 transport models (72,73). The scavenging constant λ = k Hb C Hb would be proportionally reduced in very small blood vessels.…”

Cooling strategies and transport theories for brain hypothermia resuscitation

“…Of existing compartmental models for oxygen transport, few have taken into consideration of the effect of hemodynamic factors on the transient oxygen transport in the case of circulatory arrest. Only Sharan et al [111] and Ye et al [117] studied the cerebral blood flow under three different types of hypoxia without considering the variation of hemodynamic parameters. In order to have a better insight into the role of cerebral blood flow in regulating the PO 2 in microcirculation, a model for simulating the transient blood flow, which contained the variations of vessels in arteriolar compartments, the blood flux penetrating between the vessels and the surrounding tissue should be constructed.…”