FLUID FLOW AND WALL SHEAR STRESS PROFILES IN MODEL BRANCH OF ABDOMINAL AORTA

Abstract

It has been recognized that atherosclerotic lesions tend to occur preferentially in certain areas of the arterial vessels, and that they are related to the elevated and disturbed hemodynamic forces in regions of nonuniform or complex conduit geometries sush as branch points. This finding has led many investigators to consider the relation of local hemodynamic flow patterns to the development of atherosclerosis. However, the explanation of the mechanism of development of atherosclerosis still requires reliable information on hemodynamic factors under physiologically relevant flow conditions. In the present study, flow visualization and measurements of wall shear stress have been carried out for the model conduit of a renal artery branch with a 90°take-off angle. The renal artery is characterized by side branching, and its branched shape may cause significant flow distortions and influence the wall shear stress profile. Flow visualization in the branching vessel revealed that the geometry of the branched entrance plays a significant role for the formation of a vortex in the side branch; a branched vessel, in which the proximal lip is rounded and the distal one squared, and a branch with sharp edges were employed as model renal arteries. The nature of flow in a side-branch is particularly affected by the entrance geometry. In the branch with rounded edges, no separation occurs in the proximal wall, although a secondary flow is induced due to the curved strean line. However, a separated region was generated in the branch with sharp edges, and double pairs of secondary flow appear in the side branch. We have measured the wall shear stress profile in the model renal artery branch by means of electrochemical technique. The shear stress profile in steady flow at the Reynolds number of 1000 was obtained, and the wall shear stress becomes high at the inner wall of the main branch and the distal wall of the side branch. A significant non-uniformity of wall shear stress found in the curved and branched vessels due to the three-dimensional flow structure plays an important role in the localization of atherosclerotic lesions.