Distribution of blood flow in vascular beds: Model study of geometrical,rheological and hydrodynamical effects 1

The problem of regional blood flow distribution in small vessels is considered by means of a passive model of a portion of the vascular bed. The following complexities are considered: (1) non-Newtonian behavior of blood including effects of red cell aggregation, (2) the complexity of the vascular geometry including taper, curvature and effects at bifurcations, and (3) flow unsteadiness. Three rheological models are considered, namely Newtonian, power-law and Casson fluids. It is shown that changes in flow distribution and even reversal of flow direction can occur if the fluid is non-Newtonian but not a power-law fluid. It is shown that this condition is satisfied for blood in the low flow-rate regime where erythrocyte aggregation is important. Computations indicate that local pressure changes due to inertial effects as a result of vessel non-uniformity are not important. It is suggested that alterations in blood flow distribution due to rheological changes will show up experimentally in measurements of ventilation-perfusion relationships in the lung or in analysis of in vivo dye-dilution curves.