Doctoral Dissertations

Spring 1997

Dissertation

Engineering

Degree Name

Doctor of Philosophy

Russell Carr

Abstract

As the blood flows through a bifurcation, the axisymmetric red blood cell concentration profile is skewed by plasma skimming. In the downstream segment of the bifurcation the concentration profile of red blood cells recovers symmetry by the red blood cell dispersion process.

In this study, the concentration convective equation, which models the red blood cell dispersion process, is solved with the method of finite differences in cylindrical coordinates. In the computation, a shear-induced diffusivity coefficient is used. The computed hematocrit ratios at the second bifurcation are compared with in vitro experimental data obtained from 50 $\mu$m serial trees with two bifurcations. The variable dispersion model gave the best description of experimental data. The symmetric recovery lengths are computed to compare to branch segment lengths measured in vivo. The comparison shows that for 25 $\mu$m or above microvascular vessels, the concentration profile most likely remained as asymmetric when the blood reached the next bifurcation.

A new way to measure the quantity of heterogeneity of blood flow in microvasular network based on vector algebra and conservation of mass is proposed. The heterogeneity of red blood cell flow is strongly correlated with the heterogeneity of blood flow. No correlation existed between the heterogeneity of hematocrit and the heterogeneity of blood flow. The influences of departure angle, vessel diameter and branch segment length to the heterogeneity of red blood cell flow were examined. The computational results shows that the heterogeneity of red blood cell in a 3 dimensional microvascular tree network is in the range of the heterogeneity in a 2 dimensional network. The serial tree type of microvascular network has higher heterogeneity of hematocrit and red blood cell flow than the parallel type one.

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