Experimental analysis on hemodynamic characteristics of vulnerable stenoses

Abstract

Clinical studies reported that a portion of vulnerable stenoses deformed their shapes in blood vessels based on flow conditions. Various diagnostic indices have been developed for nondeformable stenosis by using flow characteristics and resultant pressure drop across the stenosis. However, the effects of the stenotic deformation on the flow characteristics remain poorly understood. Detailed analysis on the mechanical stress exerting on a deformable stenosis is also important, because the magnitude of the stress affects to the rupture, which causes sudden cardiac death or stroke. In this study, the flows around deformable and rigid stenosis models were investigated under steady and pulsatile flow conditions. Particle image velocimetry (PIV) technique was employed to compare the flow structures around the stenosis models. Deformable stenosis models were deformed with showing high geometrical slope and height, when the flow rate was increased under steady flow condition. Three different Reynolds numbers (Re = 500, 1000, 1500) based on the inlet diameter and mean velocity were handled. The deformed stenotic shape enhanced the jet deflection toward the opposite vessel wall of the stenosis and increased the pressure drop across the stenosis models. In pulsatile flow conditions, the jet deflection in the deformable stenosis models increased the change rate of jet velocity and TKE (turbulent kinetic energy) production, compared with those of the rigid stenosis models. The effect of stenotic deformation on the pulsating pressure drop was analyzed by comparing the TKE production rates. The deformable stenosis models exhibit a phase delay of peak point in the waveform obtained by multiplying the pressure drop with flow rate at each phase. These results demonstrate the potential use of the pressure drop waveform as a diagnostic index for deformable stenoses. Previous studies tried to measure the mechanical stresses acting on the fibrous caps to predict rupture. However, most conventional measurement techniques have technical limitations of invasiveness and long processing time in evaluating the mechanical stresses. In the present study, the main determinants for fibrous cap deformation and the resultant stress were experimentally examined using deformable stenosis models. The extent of deformation and mean stress exerted on the fibrous caps are found to be closely associated with the square of flow rate divided by the fibrous cap thickness. The deformed stenotic shape directly gives rise to change the jet flow at the throat of the stenosis. Thus, the angle variation of jet flow is also correlated with the square of flow rate divided by the fibrous cap thickness. These results imply that the mechanical stress and rupture of vulnerable stenosis could be predicted by measuring the flow rate or jet angle at the throat of the stenosis in a facile manner.