Blood flow and the localization of atherosclerotic plaques.

Saphenous veins used in aortocoronary bypass procedures slowly narrow. The narrowing and atherosclerosis appear to develop in reaction to the new flow conditions present in the saphenous veins. Localization of atherosclerosis in the arterial system also suggests that local flow conditions play a role in atherogenesis; plaques are characteristically found in regions of separated flow. The pattern of separated flow in arteries is influenced by the pulsatility of arterial flow. Stagnation points delimiting flow separations migrate with each systole. An additional motion of blood, angular momentum, produces a corkscrew component to the flow. This added rotary component generates a stress that combines with the stress generated by to and fro motion of stagnation points to produce an area of multidirectional shear stress in the stagnation region. The rapidly reorienting shear stress places a special burden on the region's endothelial cells, producing an area of non-elongated cells, compromising cell internal fluidity, and modifying adhesion to neighboring cells to increase local permeability. The amount of multi-directional force generated in regions of multi-directional shear stress is increased by the flow properties of blood. Studies of blood, particularly in diabetes, will be able to characterize the factors that control the magnitude of permeability-enhancing multi-directional stress and suggest new ways to slow atherogenesis and ultimately prevent atherosclerosis.