A numerical study of flow over mild stenoses

The hemodynamic effects of arterial geometry may play a role in the localization of atherosclerosis. Various arterial geometries have been modelled to obtain local blood flow profiles in bifurcations, bends, and vessels with major stenoses. Separation zones, which may have important implications in atherogenesis, are associated with local flow and pressure disturbances due to changes in spatial geometry. Atherosclerotic plaque may cause flow disturbances such as separation zones which may lead to the growth of the initial plaque, or the initiation of another plaque downstream. In this study, steady and pulsatile flow through tubular arteries with axisymmetric stenoses of a 5% diameter reduction, and stenoses lengths of 0.5 and 0.25 diameters were studied using a numerical simulation. Flow was modelled using FIDAP, a finite element analysis program, and the wall of the arteries were assumed to be rigid with Newtonian blood flow. Steady flow studies showed the existence of a critical separation Reynolds number required before a vortex was formed downstream of the lesion. No significant recirculation was observed proximal to the lesion. Pulsatile flow studies with an infrarenal waveform (/spl alpha/=11, Re=333) showed no vortex during early systole. However, after peak systole and during diastole, separation zones were observed for the stenosed vessels. In the last part of systole, a vortex formed distal to the stenoses. During diastole, a vortex was observed both proximal and distal to the stenoses. The complex now patterns observed were a result of the mild stenoses and could be an important factor in the propagation and generation of atherosclerotic lesions.