Hemodynamics analyses of arterial expansions with implications to thrombosis and restenosis

It is assumed that critical hemodynamic factors play an important role in t he onset, localization and degree of post-operative complications, for exam ple, thrombosis and restenosis. Of special interest are sudden expansion fl ows, which may occur in straight artery segments such as the common carotid after endarterectomy or end-to-end anastomoses. Sudden expansion geometrie s are possible origins of early post-operative emboli and significant myoin timal hyperplasia resulting in early or late complications. Transient lamin ar axisymmetric and fully three-dimensional blood flows were simulated empl oying a validated finite volume code in conjunction with a Runge-Kutta part icle tracking technique. Disturbed flow indicators, which may predict the o nset of thrombosis and/or restenosis, were identified and employed to evalu ate 90 degrees-step and smooth expansion geometries. Smooth expansion geometries have weaker disturbed flow features than step e xpansion geometries. Specifically, the regions near the expansion wall and the reattachment point are susceptible to both atherosclerotic lesion and t hrombi formations as indicated by non-uniform hemodynamic indicators such a s near-zero wall shear stress and elevated wall shear stress gradients as w ell as blood particle accumulation and deposition. A new parameter, the wal l shear stress angle deviation (WSSAD) has been introduced, which indicates areas of abnormal endothelial cell morphology and particle wall deposition . In turn, regions of low wall shear stress and high wall shear stress grad ients are recognized as susceptible sites for arterial diseases. Thus, it i s interesting to note that high WSSAD surface areas cover low wall shear st ress, high wall shear stress gradient locations as well as high wall partic le deposition. A gradual change in step expansion geometry provides better results in term s of WSSAD values and hence potentially reducing atherosclerosis as well as thrombi formation. (C) 2000 IPEM. Published by Elsevier Science Ltd. All r ights reserved.