Numerical investigation of carotid stenosis in three-dimensional aortic-cerebral vasculature: pulsatility index, resistive index, time to peak velocity, and flow characteristics

Abstract

Haemodynamic correlations among the pulsatility index (PI), resistive index (RI), time to peak velocity (TPV), and mean Reynolds number (Re-Mean) were numerically investigated during the progression of carotid stenosis (CS), a highly prevalent condition. Fifteen patient-specific CS cases were modeled in the package, SimVascular, by using computed tomography angiography data for the aortic-cerebral vasculature. Computational fluid domains were solved with a stabilized Petrov-Galerkin scheme under Newtonian and incompressible assumptions. A rigid vessel wall was assumed, and the boundary conditions were pulsatile inflow and three-element lumped Windkessel outlets. During the progression, the increase in the TPV resembled that during aortic stenosis, and the parameter was negatively correlated with PI, RI, and Re-Mean in the ipsilateral cerebral region. The Re-Mean was inversely related to PI and RI on the contralateral side. In particular, PI and RI in cerebral arteries showed three second-order regression patterns: 'constant (Group A)', 'moderately decreasing (Group B)', and 'decreasing (Group C)'. The patterns were defined using a new parameter, mean ratio (lowest mean index/mean index at 0% CS). This parameter could effectively indicate stenosis-driven tendencies in local haemodynamics. Overall, the haemodynamic indices changed drastically during severe unilateral CS, and they reflected both regional and aortic-cerebral flow characteristics.