Flow separation in the renal arteries.

To determine the nature of the flow in the proximal portion of the renal arteries, a common site for the development of atherosclerosis, we performed pulsatile flow studies in a clear acrylic mold of a normal human aorta and renal arteries. The mold was developed from a cast of the renal arteries prepared in situ during the autopsy of a 27-year-old woman. Flow in the mold was visualized by the illumination of bouyant particles (100 to 300 mu). A range of branch (renal) to trunk (aorta) flow ratios of 0.053 to 0.350 was studied. Flow separation during systole was considered present when particles near the wall reversed direction. Flow separation occurred throughout systole at the superior aspect of the origin of both the left and right renal arteries at a branch-to-trunk flow ratio of 0.053. As the branch-to-trunk flow ratio increased, flow separation occurred during the deceleration phase of right renal flow. At a branch-to-trunk flow ratio of 0.350, flow separation was no longer present. This suggests that flow separation may occur near the renal ostia if renal flow falls appreciably while aortic flow remains elevated. Because flow separation involves low wall shear, mass transfer across the arterial wall may be adversely affected and possibly contribute to the formation of atheroma.