Quantitative analysis of bulk flow in image-based hemodynamic models of the carotid bifurcation: the influence of outflow conditions as test case.

Although flow-driven mechanisms associated with vascular physiopathology also deal with four-dimensional phenomena such as species transport, the majority of the research on the subject focuses primarily on wall shear stress as indicator of disturbed flow. Indeed, the role that bulk flow plays in vascular physiopathology has not been thoroughly investigated, partly because of a lack of descriptors that would be able to reduce the intricacy of arterial hemodynamics. Here, an approach is proposed to investigate, in silico, the bulk flow within the carotid bifurcation. For this purpose, we coupled a three-dimensional model of carotid bifurcation with a lumped model of the downstream vasculature. For the sake of comparison, we also imposed three different fixed flow rate repartitions between the internal and external carotid arteries on the three-dimensional model. The bulk flow was characterized by applying a descriptor of helical motion, the helical flow index (HFI) to the model; the HFI has recently been shown to provide an accurate representation of complex flows. Moreover, a new metric is presented to investigate the vorticity dynamics within the bifurcation. Our results highlight the effectiveness of these metrics in the following contexts: (i) identifying and ranking emerging hemodynamic features and (ii) quantifying the influence of the outflow boundary conditions on the composition of the translational and rotational components of the fluid motion. The metrics applied herein allow for a more comprehensive analysis, which may lead to the development of an instrument to relate the bulk flow to vascular pathophysiological events that involve not only fluid-related forces, but also transport phenomena within blood.