Markos Leggas

Document Type: Master's Thesis
Name: Markos Leggas
Email address: mleggas@att.net
Title: CHARACTERIZING ERYTHROCYTE MOTIONS IN FLOWING BLOOD
Degree: Master of Science
Program: Biomedical Engineering
Research Advisor: Eugene C. Eckstein
Advisor's email: eeckstein@utmem.edu
Committee Members: Mohammad F. Kiani
Howard Berg
 
 
Keywords: blood flow, diffusion, dispersion, rheology, suspension flow, random walk, first passage time
Availability: Release the entire work for WORLD_ACCESS.

Abstract

Characterizing the probabilistic motions of cells is a prerequisite for the development of a
general model of transport and surface deposition of white cells and platelets (WBC/P). These
phenomena differ greatly when red blood cells (RBC) are present at normal levels, but follow
convective diffusion in dilute suspensions. A critical need is to understand and characterize
dispersion and diffusion as they apply to red cells in suspension flow. The dispersive motions of
0.5-micrometer beads and fluorescently labeled human RBC flowing in dilute (0.003%) and
concentrated (25%) RBC suspensions, respectively, were characterized using fluorescence
videomicroscopy methods, and times for individual tracer particles to move fixed distances were
measured. The particles were tracked in the axial direction and in a moving reference frame. The
experimentally estimated effective diffusion coefficient of the particles was in good agreement
with published work (RBC ~ 1x10 -8 and beads ~ 4x10 -9 [cm 2 /sec]). Using a continuous time
random walk model (CTRW) to characterize the particles’ random motions in a shear field, the
average time was plotted versus the squared displacement and a power law fit exponent was used
to quantitatively distinguish between diffusion and dispersion. Values consistent with Brownian
motion were found for the bead suspensions and an anomalous diffusion was found for the RBC
suspensions, which indicated that beads random motions were diffusive and the RBC ones were
dispersive. The methods developed in this work could be used to study dispersion events at
different lateral locations along the channel’s height and investigate the effects of flow
parameters such as wall shear rate, hematocrit, and cell type.

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Revised 23 May 2002