The pattern of endothelial geometry at various locations along stenosed dog aortas was examined. This was done to test the hypotheses that the shape of an endothelial cell is related to the local wall shear stress associated with the flowing blood and that alterations in hemodynamics, produced by vascular geometrical changes, influence endothelial cell geometry. Aortic stenosis with a reduction of 71% of the cross-sectional area was produced. The animals were sacrificed 12 weeks later, and the endothelial cell geometry and orientation were studied using the vascular casting technique and a computerized analysis to determine cell area and shape index. The regions of the stenosis examined were those known to experience different hemodynamic conditions. The value of the shape index was found to fall rapidly in the convergent region of the stenosis and to increase suddenly in the divergent region, eventually returning to the prestenotic value at a more distal site. Using a model of a stenosis made from a vascular cast, laser Doppler anemometry was applied to measure velocity profiles and to estimate the local wall shear stress in a stenosed aorta. It is shown that the shape index distribution along these stenosed vessels may be correlated with the level of wall shear stress, with more elongated cells occurring in regions of higher shear stress. (Arteriosclerosis 6:220-229, March/April 1986) T he evidence for the involvement of fluid dynamics in the atherosclerotic process centers primarily on the pattern of the disease.1 " 3 It is often regions of arterial branching and sharp curvature that have the greatest predilection for the development of atherosclerosis. These are also regions where the flow will assume unusual characteristics or at least deviate from what otherwise might be considered a well-behaved arterial flow. The indictment provided by this indirect evidence, particularly as it relates to the bifurcations and geometrical contortions of the arterial vasculature, presently motivates much of the interest in arterial fluid dynamics.It has been suggested that vascular geometry may affect the atherogenic process through its influence on the hemodynamic environment to which the intima is exposed. 4 ' 5 Under such a hypothesis, whatever affects vascular geometry would alter the local detailed flow characteristics and correspondingly influence endothelial morphology and function. Our interest in hemodynamic Received November 5,1984; revision accepted November 12, 1985. forces, in particular arterial wall shear stress, stems from the belief that it is through this hemodynamically imposed frictional force that a fluid mechanic effect on the endothelium becomes manifest. In this context, the topic of interest is the influence of hemodynamic forces on endothelial morphology, cell function, cell turnover rate, and transendothelial transport, and it is the first of these, endothelial morphology, more specifically, en face cell shape, which is the subject of this investigation.There is a body of accumulating data th...

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Geometric changes from the symmetrical to the asymmetrical ACoA develop higher shear stress on the ACoA than critical values and the stagnation point at the ACoA junction. A combination of these hemodynamic factors is considered to play an important role in initiation of aneurysm.

Basic flow patterns were investigated in a set of glass aneurysm models by means of flow visualization methods. Dye injection and streaming double refraction were used to visualize flow. The circulation inside lateral aneurysms arising at a 90 degree angle from a straight parent conduit could not be visualized by the dye-injection technique but could be demonstrated by streaming double refraction. The inflow was seen to arise from the downstream lip of the orifice and to project to the dome of the aneurysm. Backflow to the parent conduit took place along the walls of the aneurysm. In aneurysms located at bifurcations, flow characteristics depended on the geometry of the bifurcation and the flow ratio between the branches. Relatively little intra-aneurysmal flow was demonstrated in side branch-related aneurysms arising distal to an asymmetric 90 degrees bifurcation of the type encountered at the junction of the internal carotid and posterior communicating arteries. Stagnation of flow at the neck and little intra-aneurysmal circulation were found with terminal aneurysms of the basilar bifurcation type if the outflow through the branches was symmetric. With asymmetric outflow, however, or if the axis of the aneurysm did not coincide with that of the afferent vessel, an active rotation developed in these aneurysms. The size of the aneurysm had no influence on the basic pattern of intra-aneurysmal circulation. The use of pulsatile perfusion did not significantly alter the basic flow patterns observed with steady flow. Locally disturbed laminar flow was observed in certain models at physiological Reynold's numbers, but there were no signs of fully developed turbulence.

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