R. Perrault

Computational Approach to Estimating the Effects of Blood Properties on Changes in Intra-stent Flow

In this study various blood rheological assumptions are numerically investigated for the hemodynamic properties of intra-stent flow. Non-newtonian blood properties have never been implemented in blood coronary stented flow investigation, although its effects appear essential for a correct estimation and distribution of wall shear stress (WSS) exerted by the fluid on the internal vessel surface. Our numerical model is based on a full 3D stent mesh. Rigid wall and stationary inflow conditions are applied. Newtonian behavior, non-newtonian model based on Carreau-Yasuda relation and a characteristic newtonian value defined with flow representative parameters are introduced in this research. Non-newtonian flow generates an alteration of near wall viscosity norms compared to newtonian. Maximal WSS values are located in the center part of stent pattern structure and minimal values are focused on the proximal stent wire surface. A flow rate increase emphasizes fluid perturbations, and generates a WSS rise except for interstrut area. Nevertheless, a local quantitative analysis discloses an underestimation of WSS for modelisation using a newtonian blood flow, with clinical consequence of overestimate restenosis risk area. Characteristic viscosity introduction appears to present a useful option compared to rheological modelisation based on experimental data, with computer time gain and relevant results for quantitative and qualitative WSS determination.

Blood flow in stented coronary artery : numerical fluid dynamics analysis

Recent generalization of stent implantation in interventional cardiology require full understanding of blood flow cartography. Interdepency between fluid stresses and in vivo cells covering lumen artery are regularly accused to be one of the instigator of neointimal proliferation (thickening of the inner layer of blood vessels) and mid-term restenosis. This study purpose to numericaly investigate the three dimensional flow in vicinity of an endoprothesis. We used a finite element method to simulate a steady flow of non-Newtonian fluid in a coronary artery using a rigid wall approximation. Results on the velocities, wall shear stress and wall shear stress gradients are presented. Theses simulations allow identification of stagnation site and low wall shear stress area that may be prone to clot formation and neointimal hyperplasia. Intra stent flow knowledge can potentially contribute to optimization of prothesis design and decreasing second intervention rate.

Experimental study of blood laminar flow through a stented artery

The objective of this research is to study the blood flow close to the wall of a stented artery. Indeed, previous works have showed that the restenosis phenomenon is induced by the endothelial cells stimulation due to the wall shear stress values. The coronary angioplasty is responsible of wall shear stress modification, mainly between the stent struts, at the inlet and the outlet of the endoprothesis. That is why, to study the flow disturbances through a stented section, we built an in vitro model reproducing the struts shapes of a marketed endoprothesis. The experimental artery is composed of a see-through square section vein, which reproduce the struts design with a magnitude of 100. A programmable pump provide a steady or a pulsatile flow. By using the velocimetry per imagery of particle (PIV) optical method we have explored the flow between and over the stent branches, in order to assess and to quantify the wall shear stress and to locate the interesting zones.

Determination of the optimal region for interaliasing distance measurement for flow regurgitant rate calculation: a fluid simulation study

BACKGROUND Color Doppler imaging of the convergent region is promising for quantifying valvular regurgitation. Nevertheless, proximal isovelocity surface area method has limitations. We sought to determine the optimal localization to measure the most precise flow rate using a new approach: the interaliasing distance. METHODS A finite volume-based program was used to perform simulations in unsteady flow conditions. Different instantaneous flow rates, leaflet angles, and orifice sizes were tested reproducing physiologic conditions. Relative difference between actual and interaliasing distance flow rate was calculated for each configuration. RESULTS The relationship between the relative error and the aliasing velocity location was described by a third-order polynomial equation. The magnitude of relative error is a function of the flow rate, orifice size, and leaflet angle. CONCLUSION The optimal distance from the orifice to measure the interaliasing distance was when the closer aliasing was between 4 and 8 mm from the orifice.

Unsteady 3D simulation of intra stent flow

Vascular damage inflicted during the deployment phase of stent placement causes partial denudation of the endothelial cell layer uncovering the smooth muscle cells and preserving some endothelial cell. Vascular denudation consequence is a direct interaction between blood flow and vascular layer component. It is also commonly suggested that the presence of a foreign body in the arterial lumen can induce significant variations in the flow topology in comparison to the “standard” physiological flow patterns that are usually seen in hemodynamic literature. Although the flow remains laminar, it undergoes major changes in terms of its spatial and temporal wall shearing values. Consequences are a possible non negligible cellular proliferation which could lead to partial or total restenosis. Based on this precept, it is therefore legitimate to estimate that hemodynamic changes may be partly responsible for the intra stent restenosis problem. The aim of our recent research is to numerically investigate intra stent blood flow for unsteady inlet condition using a characteristic viscosity and rigid wall assumption. Results could give relevant information to estimate restenosis risk for the stent design studied.

The mitral valve prolapsus: quantification of the regurgitation flow rate by experimental time-dependant PIV

Color Doppler is routinely used for visualisation of intracardiac flows and quantification of valvular heart disease. Nevertheless the 2D visualisation of a complex 3D phenomenon is the major limitation of this technique. In particular, in clinical setting, the flow rate calculation upstream a regurgitant orifice (i.e. mitral valve insufficiency), assumes that the velocity field in the convergent region have hemispheric shapes and introduce miscalculation specially in case of prolapse regurgitant orifices. The main objective of this study was to characterize the dynamic 3D velocity field of the convergent region upstream a prolapse model of regurgitant orifice based on 2D time dependent PIV reconstruction.

Cardiac simulations of regurgitant jets in mitral valve, for different pathological cases, in steady and pulsatile flow

In order to assess the quantification of valvular heart insufficiency in adult echocardiography, we simulate flow dynamics in different models of mitral regurgitation (shapes and sizes) in steady and unsteady flow. The length, width and contraction coefficient of potential core, defined as the velocity zone where velocities are equal or superior to orifice velocity, obtained with physiologic and pressure flow conditions, were nearly the same for each pathologic case (perforation, restrictive form and prolapsed case). The simulation was realised on several cardiac cycles, to see the evolution of jets with time. To validate the numerical model, we have developed an experimental bench with laser plane and ultrasound methods to get the velocity field and jet characteristics.