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.
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.
Abstract-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 seethrough 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.Keywords-Stent, endoprothesis, coronary artery, restenose, wall shear stress, endothelium cell. I.INTRODUCTIONFor several years the leading cause of morbidity and mortality in the developed countries has been the whole of the disorders of the cardiovascular system and mainly the phenomenon of stenosis in coronary arteries. Since the 80's, there is an alternative to the usual balloon angioplasty. Indeed, the use of tiny metallic scaffolds (named coronary endoprothesis or stent) has surpassed all expectations. Now, the use of the technique of stent is generalized in practical clinic (representing 60-90 percent of procedures), approximately 1,000,000 patients worldwide undergo a non surgical coronary artery interventional procedure yearly. A coronary stent is a small, slotted, stainless steel or nickel tube mounted on a balloon catheter, which remains in the artery. The procedure is the following one: the coronary stent is placed over the angioplasty balloon and moved to the site of lesion. The stent expands with the balloon and remains in place after the balloon is deflated and removed, thereby serving as a mechanical scaffold to prevent restenosis.Unfortunately, there is still a very important disadvantage. Indeed the rate of restenosis, response to stent implantation, still occurs frequently (in 20% or 40% of cases). In-stent restenosis occurs mainly at the area of the injury vascular induced by the implantation of the endoprothesis but not exclusively. It also frequently appears in all the zones where the flow can be disturbed , in particular between the branches of stent. The composition of in-stent restenosis includes vascular smooth muscle cell and endothelium cell i.e. it consists predominantly of neointimal growth. Previous study showed that the areas of endothelium exposed to a low and oscillating stress correspond to the places where the restenosis develops preferentially [1], indeed, endothelium cells are an interface extremely active, able to bring an answer differentiated according to the stresses physics of its environment [2]. The...
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