Stratified multiphase model for blood flow in a venular bifurcation.

Available in vitro and in vivo experimental observations suggest that red cell aggregation and blood vessel geometry are important determinants of the flow characteristics of blood in venules. However, no consistent relationship has been observed between red blood cell aggregation and vascular resistance. The present work attempts to understand this relationship by evaluating computationally the effect of red cell aggregation on the flow characteristics of blood in a converging vessel bifurcation. The proposed mathematical model considers blood as a two-phase continuum, with a central core region of concentrated red cell suspension that is surrounded by a layer of plasma adjacent to the vessel wall. In the central core region, blood is described by Quemada's non-Newtonian rheological model, in which local viscosity is a function of both the local hematocrit and a structural parameter that is related to the size of red blood cell aggregates. Fluids from the two feeding branches are immiscible, which results in a stratified multiphase flow in the collecting venule. Calculations predict a complex, three-dimensional pattern of blood flow and generally nonaxisymmetric distribution of velocity, hematocrit, and shear stress in the collecting venule. The calculations are a first step toward a realistic model of blood flow in the venous microcirculation.