基于低切应力学说的动脉粥样硬化发展数值模拟

发布时间：2018-05-18 02:04

本文选题：血流动力学 + 数值模拟　；参考：《郑州大学》2017年硕士论文

【摘要】：据《中国心血管病防治现状蓝皮书·2015》报道,目前我国约有2.9亿心血管病患者且呈现出逐年上升的趋势。每一年就有约260万人因心血管疾病而死亡,平均每12秒就有1人被心血管疾病夺去生命,其发病率和死亡率位居所有疾病的首位。对人类健康这一公共卫生问题构成严重威胁,亟待通过多方研究加以解决。动脉粥样硬化(Atherosclerosis,AS)是一种常见的血管疾病,可能会引起脑卒中、冠心病、心肌梗死等严重并发症。对于60岁以上的老年人,其发病率高达79.9%。如果同时伴有心脑血管疾病,患者5年内的生存率只有59%,而对于“三高症”患者,其生存率更低。由此可见,AS对于人类健康具有严重的潜在威胁。但是,AS的致病成因和发展机理较为复杂,尚未被完全认知掌握。探索AS的发病规律和具体原因,对于病情控制、风险评估以及临床预后工作都具有十分重要的意义。大量研究表明,动脉粥样硬化的发展受到生物、物理、化学等多方面刺激的影响。各方学者也依据相关病例及实验结果,提出了各种学说试图解释AS的产生与发展机理。但这些学说均没有系统的分析AS产生与发展过程中的力学机理。Caro在对尸体的解剖研究中发现,AS主要发生于分岔、狭窄、弯曲等血流动力学易受扰动的部位,表现出非常明显的无差异局部病灶性特征,从而证明血流动力学环境的改变对AS的形成和发展具有重要影响,但对于其具体作用方式和影响程度的了解还不深。本文的研究思路是采用逆向工程建模,通过数值仿真证明血管形貌会对管壁受力造成一定影响,导致局部壁面切应力较低。随后再结合Caro低切应力学说,利用被动式动网格方法,将壁面切应力作为判据,模拟AS的动态发展过程。本文的模拟计算工作是通过FLUENT计算流体动力学软件完成的,其操作界面简洁美观,具有丰富的物理模型以及先进的数值算法,还具有配套的前后处理功能。在计算流体领域认可度较高,计算结果也较精确可靠。FLUENT还提供了二次开发的程序接口(UDF),方便用户实现更多元化的模型求解功能。本文以血流动力学为切入点,考虑壁面低切应力对斑块增生的促进作用以及流场边界的变化对血液流动重分布的影响,实现血管壁边界变化与血流动力学之间的相互耦合作用,这也正是此方法的技术难点。本文在考察主动式动网格和单元填充法后,发现其模拟效果和计算效率存在不足。为此,本文创新性的采用了二次开发的UDF(User Defined Function)动网格程序,实现在计算过程中提取血管壁面切应力并做出判断,进而调控动网格节点的移动,模拟血管斑块的增生过程。经过对比,发现模拟结果与一些临床血管造影的相似度较高,证明了本方法的可行性。
[Abstract]:According to Blue Book 2015, there are about 290 million patients with cardiovascular diseases in China. Every year, about 2.6 million people die from cardiovascular disease, and an average of one person is killed by cardiovascular disease every 12 seconds, the highest morbidity and mortality rate of all diseases. It poses a serious threat to the public health problem of human health, and needs to be solved in many ways. Atherosclerotic Atherosclerosis (ASA) is a common vascular disease, which may cause severe complications such as stroke, coronary heart disease, myocardial infarction and so on. For the elderly over 60 years old, its incidence is as high as 79. 9%. If accompanied by cardio-cerebrovascular disease, the 5-year survival rate is only 59, and for the "three high" patients, the survival rate is even lower. This shows that as has a serious potential threat to human health. However, the pathogenetic and developmental mechanism of as is complicated and has not been fully understood. It is of great significance for disease control, risk assessment and clinical prognosis to explore the pathogenesis and causes of as. Numerous studies have shown that the development of atherosclerosis is influenced by biological, physical and chemical stimuli. According to the relevant cases and experimental results, scholars have put forward various theories to explain the mechanism of as production and development. But none of these theories systematically analyzed the mechanical mechanism in the process of as production and development. Caro found in the autopsy of cadavers that as mainly occurred in bifurcation, stenosis, bending and other hemodynamic easily disturbed sites. It is proved that the change of hemodynamic environment has an important influence on the formation and development of as, but the specific mode of action and the degree of influence are not well understood. The research idea of this paper is to use reverse engineering modeling. The numerical simulation results show that the shape of blood vessel will have a certain effect on the wall force, resulting in a low shear stress on the local wall. Based on Caro's theory of low shear stress and passive dynamic grid method, wall shear stress is taken as criterion to simulate the dynamic development of as. The simulation and calculation work in this paper is accomplished by FLUENT computational fluid dynamics software. The operation interface is simple and beautiful, it has abundant physical models and advanced numerical algorithms, and it also has the function of pre-processing and pre-processing. In the field of computational fluid recognition is high, the calculation results are more accurate and reliable. Fluent also provides a secondary development of the program interface to facilitate users to achieve more diversified model solving functions. In this paper, we consider the effect of wall low shear stress on plaque proliferation and the effect of flow field boundary change on blood flow redistribution, so as to realize the interaction between vascular wall boundary change and hemodynamics. This is the technical difficulty of this method. After investigating the active dynamic mesh and element filling method, it is found that the simulation effect and computational efficiency are insufficient. In this paper, the second developed UDF(User Defined function dynamic grid program is used to extract the wall shear stress and make the judgment in the process of calculation, and then to regulate the moving of the dynamic grid node and simulate the plaque proliferation process. By comparison, it is found that the simulation results are similar to some clinical angiography, which proves the feasibility of this method.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O39;R543.5

【参考文献】