Distant hemodynamic impact of local geometric alterations in the arterial tree

Abstract

Hemodynamics has long been identified as a major factor in the determination and localization of atherosclerotic lesions. Atherosclerosis is focal and often forms in specific locations in the arterial tree such as bifurcations. Many different aspects of fluid mechanics have been suggested as the trigger for atherogenesis - non-laminar and/or unstable flow, flow separation, regions of higher/lower and/or oscillatory shear stress etc. While the precise mechanism by which these hemodynamic factors act is not yet clear, the fact that they correlate highly with atherogenesis suggests that local disturbances in flow through blood vessels can promote arterial disease. These issues have become increasingly acute as physicians seek to alter the pathological arterial anatomy with bypass grafting or endovascular manipulations such as angioplasty or stenting. We proposed that vascular interventions might cause previously unforeseen effects in the arterial tree especially at branch points. Manipulation of one branch of a bifurcation might adversely affect the contralateral branch of the bifurcation. The goal of this work was to study the distant impact of local flow alterations, as well as to classify and evaluate the different parameters that determine their severity. Dynamic flow models of the arterial system were developed that allowed for the continuous alteration of model geometry in a controlled fashion. This property allows for the simulation not only of the healthy or diseased states, but also of the entire range in between. Moreover, these models permit simulation of different strategies of clinical intervention. Flow through the models was investigated using both qualitative (flow visualization) and quantitative (flow and pressure readings) tools. Flow separation and vascular resistance in one location of the arterial tree varied with geometrical alterations in another. The results of this study could have important implications for the diagnosis, treatment and long-term follow-up of the large number of patients who suffer from these diseases and undergo vascular interventions. Clinical arterial manipulation of one arterial site may well need to consider the hemodynamic impact on vascular segments at a distance.