Steady flow visualization in a rigid model of the aortic bifurcation: Application to atherosclerosis

Abstract

Hemodynamics have long been implicated in atherogenesis. The studies reported here seek to explain the mechanisms for the formation of atherosclerotic plaque in an aortic bifurcation. Flow studies were made in a model constructed from plexiglass to represent an aortic bifurcation. Under steady flow conditions at inflow Reynolds numbers of 80-1250, the streamline flow patterns and the boundary layer separation zones were investigated in relation to the location of atherosclerotic plaques clinically found at regions in the human aortic bifurcation. The streamline flows were visualized by a slow injection of dye over the cross section of the tube entrance and along the tube walls. The studies revealed a complex flow field where secondary flows, induced by the centrifugal and viscous forces, cause the fluid to move towards the inner walls of the aortic bifurcation. The effect was more clearly seen with increasing Reynolds number. Boundary layer separation zones were observed to occur at the outer corners of the branching. The nature of the separation zone formed was found to be dependent on Reynolds number. The residence time of fluid particles within such a separation zone was estimated by measuring the washout time of a bolus of dye injected at strategic locations along the tube walls. The residence time was found to decrease exponentially with increasing Reynolds number. These observations provide strong support for the role of flow separation in the accumulation of LDL and platelet aggregation within the aortic bifurcation.