Effect of particle collisions and aggregation on red blood cell passage through a bifurcation

Blood flow through bifurcating vessels in the microvasculature leads to uneven distribution of red blood cells (RBC) in the downstream channels when the channels have different sizes or the flow rates through the channels are different. This phenomenon, known as plasma skimming, is responsible for the large variation in hematocrit throughout the circulatory system. Furthermore. the strong streamline curvature present within bifurcations leads to frequent collisions between the blood elements (red and white blood cells and platelets) and the vessel walls, as well as a rearrangement of the distribution of the blood elements in the channels downstream of the bifurcation. Computational models of bifurcation flows typically neglect collision and adhesion of RBCs with each other. In this paper, we use a new type of discrete-element model to investigate the effect of particle-particle collisions and RBC aggregation on modeling of plasma skimming in bifurcations. Cases are examined with and without RBC adhesion and for different hematocrit values, including validation against previous computational results. Results show significant plasma skimming in the low-flow daughter branch and an increase in fractional particle flux with increased hematocrit, as in experimental studies. Accounting for particle-particle collisions leads to a considerable increase in collision rate of particles with the vessel wall. Particles are found to approximately follow fluid velocity streamlines, and consequently particle-particle collisions and aggregation do not significantly affect plasma skimming. (C) 2009 Elsevier Inc. All rights reserved.