Distribution of blood flow in vascular beds: model study of geometrical, rheological and hydrodynamical effects.

Abstract

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 g eometry 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.