Red Blood Cell Flux in Isolated Capillary Bifurcations

Abstract

Capillary red blood cell (RBC) flux is the most important determinant of oxygen delivery to tissue. Simultaneous experimental measurement of flow throughout a microvascular network is impractical and necessitates predicting flow using computer simulations. Our existing model uses an empirically derived bifurcation rule (Pries et al., 1989) to determine RBC distribution between daughter branches. Our objective is to validate the existing model of microvascular blood flow on capillary networks versus in vivo measurements. Capillary networks in rat skeletal muscle were recorded and 4 capillary bifurcations were randomly selected for analysis (diameter 5.9±0.27 ?m, segment length 107.7±28.8 ?m). Custom vascular mapping software was used to reconstruct the real geometry of each bifurcation. Each capillary was analyzed to measure RBC velocity, tube hematocrit and RBC flux. The error in measured RBC flux in the parent compared to the sum of daughters was 1.9±8.3%. Discrete fluctuations of cell distribution over time were seen to have a significant impact on measured flux fraction (FF). Measured RBC FF in the higher flow daughters were 9±6.3% lower than the bifurcation rule predicted at equivalent flow rates. The stochastic nature of the bifurcation rule makes precise predictions of RBC distribution difficult where alternating cells paths can drastically impact measured FF.Supported by CIHR grant to DG and CGE.