| BACKGROUNDCoronary Atherosclerotic Disease (CAD), generally referred to as the coronary heart disease, or coronary heart disease, due to coronary atherosclerotic vascular cavity stenosis or occlusion, and (or) functional change of coronary arteries (spasm), could led to myocardial ischemia or necrosis. Pathologic basis of CAD is coronary atherosclerosis and90%of clinical coronary events were caused by coronary atherosclerosis. Currently recognized risk factors include high blood pressure, high cholesterol, high cholesterol, high cystine hematic disease, high blood sugar, smoking, overweight, obesity, genetic factors, and inadequate intake of trace elements, etc. Long-term complicated chronic inflammatory process promotes and accelerates the occurrence and development of atheromatous plaque. It is confirmed that CAD is affected by many factors, Including genetic, metabolism, and environment, especially, inflammatory mediators. Artery blood flow changes and lipid deposition play a significant role in the occurrence, developing, and break of plaque. There are many kinds of disease theory in trying to explain the pathogenesis of atherosclerosis, such as lipid invasion theory, monoclonal theory, theory of shear stress and damage theory, theory of homocysteine, endothelial dysfunction theory, theory of arginine, oxidative stress, endothelial progenitor cells function aberration theory, etc., but it is still not completely clarified the mechanism of occurrence and development of atherosclerosis and its influencing factors. Huge burden of prevention and treatment of coronary heart disease arised because of high prevalence and mortality of CAD with enormous high risk groups. Except the primary prevention of CAD, such as lifestyle intervention and risk factors, a large number of screening of coronary heart disease in susceptible crowd is also an important way to the prevention and treatment of CAD.However, due to technical difficulties, in vivo or in vitro experimental study of hemodynamics is not workable. Coronary blood flow could lead to the nonuniformity distribution of lipid, white blood cells, platelets and other visible ingredients. Local large hemodynamic changes often accompany with slow flow and retention of blood that may cause the deposition of the visible ingredients in the blood, and gradually the atheromatous plaque appear and develop until lead to stenosis and ischemia of the related vascular control area, eventually patients showed obvious clinical symptoms. Researches on numerical simulation of blood flow in recent years find that atherosc-lerosis prone to occurs in cerebral arteries, carotid artery and coronary artery that owns vascular branch or a sharp bend, however, the above risk factors are not fully explain the localized sclerosis. So we can speculate that there are some selective positioning function of pathogenic factors might be related to plaque formation on the obvious tendency of anatomy. The purpose of our study is hence to computationally analyze the differences between geometry and hemodynamics of the different anatomic structure of right coronary artery and the highly curved coronary arteries with various eccentric stenosis.Part I Numerical Simulation of the Normal Right Coronary Artery[OBJECTIVE]The purpose of our study is hence to computationally analyze the wall shear stress (WSS) and wall pressure gradient (WPG) variations in idealistic and realistic right coronary arteries (RCAs), for exploring the hemodynamic differences between RCAs with or without tortuosity and providing the basis for the clinical evaluation of tendency to plaque.[METHODS]The geometry of our arterial models was designed based on the anatomical details of the real RCAs. The straight geometry model with angulation angle of60°between the trunk and side-branch in the vertical plane was derived as the reference model and which was established by Proe5;125other models have been generated, by changing:(i) the curvature of the trunk;(ii) the curvature of the side-branch;(iii) the angle γk between the trunk and side-branch.The original DICOM format images of patients with suspected coronary artery disease were imported into Mimics10.01, where image segmentation was carried out and the optimized mask model of RCA was primarily constructed. Then three RCAs were selected and were depicted and labeled as A, B and C:model A appeared as a C-shape artery, namely RCA without tortuosity, model B was its S-shape counterpart, while model C had more curves appearing at different segments along the trunk of the artery, namely RCA with tortuosity. At last, RCAs were post-processed with Geomagic studio2012by means of geometrical trimming and smoothing.The volume meshes and boundary layer meshes were generated in CFX, and the numerical simulation was performed under the same physiological boundary conditions and solving condition. We selected the WSS and WPG distribution on the artery, as well as wss on the wall and the pressure drop (△P) between the inlet and outlet of the models as the simplest metrics at peak systolic moment.[RESULTS]We can postulate that, in simulated RCAs, the atherosclerotic plaques are more prone to be located at the relatively low WSS and WPG sites of the curved arterial trunk and its branch for arbitrary degrees of curvature. The results show that increasing values of wss and△P are in positive correlation with the increasing of (i) the curvature of the trunk;(ii) the curvature of the side-branch;(iii) the angle y^between the trunk and side-branch.In the realistic RCAs, results shows that:(i) the realistic RCAs shapes as ’complex wall geometry" that directly affects the hemodynamic parameters WSS and WPG;(ii) there are more of the less intensified WSS regions that are noticed opposite to the angulation and inner wall of the curve;(iii) the high WSS are always located adjacent to the bifurcation, and (iv) the WSS is higher at the proximal particularly evident by contrasting the high WSS at bifurcation;(v) the wss and△P of artery C are higher than that of arteries A and B.The analysis results of realistic models are found to be consistent with the results observed in the simulated artery models. However, the AP of arteries A, B and C are two to three times greater than the idealistic models due to the complex geometry of realistic models. This indicates the difference between realistic models and idealistic models, as the realistic models represent the patients’actual arterial geometry, while the simulated models do not incorporate the complex wall geometry such as the tortuous appearance of the vessel wall.[CONCLUSIONS]In this paper, we have constructed a parametric study framework that is built on idealistic coronary models, which we have used to evaluate the effect of curvature of RCAs and various angulations of the side-branches on the hemodynamic characteri-stics based on realistic coronary models. It has been shown that the local low WSS and WPG regions sited at the plaques prone points are consistent with the data derived from literatures, and shows a marked difference in both magnitude and spatial distribution of WSS and WPG among all the simulated models, thereby demonstrating the hemodynamics differences among the models with diversity in anatomy. Further, our study is clinically important in also providing the basis and causes of flow resistance assessment causing pathological lesions, and can provide a basis for surgical design and construction of coronary arterial bypass grafting. Part II Fluid-structure Interaction Analysis of Highly Curved Coronary Arteries with Various Eccentric Stenosis[OBJECTIVE]Elastic two-way fluid-structure interaction analysis (FSI) between the blood vessel wall and blood was carried out to investigate the hemodynamic differences in highly curved coronary arteries with various eccentric stenosis.[METHODS]The coronary arteries without and with varying degrees of eccentric stenosis based on area stenosis percentage were established by Proe5. In principle, we assumed that a plaque grows longitudinal and lateral with a greater degree of lumen stenosis.The solid domain is constructed in the ANSYS solver, while the fluid domain is modeled in the CFX solver. The coupling between the solid and fluid domains is from the’setup’of the two solvers. FSI was performed under the same physiological boundary conditions and solving condition. We selected the WSS, WPG and von Mises stress distribution on the artery, as well as the WSS on the wall,△P between the inlet and outlet and von Mises stress values at the throat of the stenosis as the simplest metrics at peak systolic moment.[RESULTS]Low WSS regions are always occurring at the inner wall and moving from center to downstream of inner wall along the development of stenosis while low WPG regions moving from distal part to downstream of inner wall. Von Mises Stress is no uniformly distributed at the throat of the stenosis. The increasing of WSS on the wall,△P between the inlet and outlet and von Mises stress values at the throat of the stenosis is positively correlated with the increased height of the plaques based on the unobstructed vessel wall. [CONCLUSIONS]Herein, computational modeling of atherosclerotic arteries in this research has been performed, by taking into consideration the structural modifications of stenosis variations. It has been shown that the local low WSS and WPG regions sites at the plaques prone points are consistent with the data derived from literatures of anatomical and clinical researches, which can be used to gain insight into the formation of plaque. Our flow analysis hemodynamic data of△P in atherosclerotic vessels is sufficient to serve as the reference data for the assessment of flow resistance through varying arterial structures and von Mises stress for predicting the plaque rupture. |
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