Simulated Two-Dimensional Red Blood Cell Motion, Deformation, and Partitioning in Microvessel Bifurcations
by
Jared Barber
Program in Applied Mathematics, University of Arizona
Coauthors: Jonathan P. Alberding, Juan M. Restrepo, Timothy W. Secomb

Movement, deformation, and partitioning of mammalian red blood cells (RBCs) in diverging microvessel bifurcations are simulated using a two-dimensional, flexible-membrane model. A set of viscoelastic elements represents the RBC membrane and the cytoplasm. These elements are coupled to finite elements that represent the surrounding fluid and the coupled system is numerically solved. Simulated isolated RBC trajectories deviate from background flow streamlines primarily because of cell migration towards vessel centerlines and cell obstruction of downstream vessels. Estimates of RBC distributions at a bifurcation are determined as a function of total blood fluxes into the two branches and upstream RBC spatial and velocity distributions. RBCs preferentially enter the higher-flow branch, leading to unequal RBC fluxes in the downstream branches. Cell migration gives cells a stronger tendency to enter the high flow branch. Cell obstruction, on the other hand, counteracts this tendency. In unequally-sized daughter vessels, partitioning is asymmetric, with RBCs tending to enter the smaller vessel. Partitioning is not significantly affected by the daughter vessel orientations. Significant differences are found between rigid particle and flexible cell distributions. Predicted distributions with flexible cells are consistent with experimental observations, showing that membrane flexibility is an important factor determining realistic RBC distributions in bifurcations.

Date received: May 14, 2008