A model for red blood cell motion in bifurcating microvessels

A theoretical model is developed for red blood cell motion in a diverging microvessel bifurcation, where the downstream branches are equal in size but receive different flows. The model is used to study migration of red cells across streamlines of the underlying flow, due to particle shape and flow asymmetry. Effects of cell–cell interactions are neglected. Shapes of flowing red cells are approximated by rigid spherical caps. In uniform shear flows, such particles rotate periodically and oscillate about fluid streamlines with no net migration. However, net migration can occur in non-uniform flows due to the particles’ lack of fore-aft symmetry. A nonuniform flow field representative of a bifurcation is developed: flow bounded by two parallel plates, and divided by a cylindrical post. Significant migration is found to occur only with a nonuniform and asymmetric distribution of upstream orientations. The model suggests that the assumption made in previous models of bifurcations, that red cells follow fluid streamlines, is justified if cells approach the bifurcations with random orientations.