【作者】 张潇；

【导师】 袁泉；

【作者基本信息】 山东大学 ， 机械工程（专业学位）， 2016， 硕士

【摘要】 随着人民生活水平的提高和老年人口数量的增加,心血管疾病的发生率有所增大,其中心脏瓣膜疾病属于心血管疾病的一种。瓣膜发生病变后危及患者生命安全、降低生活质量,还给其家人及社会造成沉重的压力和负担。通常造成心脏瓣膜发生病变的原因有结构组织功能性退化、应力应变引起疲劳损坏和外界原因造成瓣叶钙化。对病情较重的患者而言,有效的治疗手段是及时更换心脏瓣膜。生物瓣膜与人体心脏瓣膜极其接近,具有相似的血液动力学性能,置换后患者无需终生抗凝治疗,而且引起的并发症较少。但是生物瓣膜有其自身材料特性,在不断受到血流冲击的影响下,会发生瓣叶钙化、退化和撕裂,这明显缩短了生物瓣膜的使用寿命。因此,致力于提高生物瓣膜的耐久性,找出瓣叶的破损原因,设计出具有优良性能的生物瓣膜是当前的重要任务。本论文通过提取医学影像扫描数据,将得到的心脏扫描二维图像利用三维建模软件打开,并通过阀值提取、编辑修改、区域增长以及二次网格划分等工具完成心脏瓣膜和动脉壁的重建。配合逆向软件对模型做点云处理、多边形处理和曲面分析对模型做进一步优化,使之最终能够导入有限元分析软件。所建模型不但可以真实地表达人体心脏瓣膜结构的外型特征,还能利用有限元分析软件进行模拟仿真得到相应的应力、应变数据,对体外试验是有力补充。利用有限元分析软件ANSYS Workbench,对瓣叶施加动态压力来模拟血液冲击瓣叶的过程,其中瓣叶的材料设置来源于临床数据。通过有限元应力应变分析结果表明：瓣叶撕裂与瓣叶所受的最大应力和应力集中程度有关,最大应力和应力集中的区域一般容易发生瓣叶损坏和破裂,其发生部位主要在瓣叶受力最大的缝合边。心脏瓣膜厚度一般是0.25-0.5mm,通过改变瓣叶的厚度对瓣膜进行动态力学性能分析,发现：当瓣叶厚度为0.4mm时,瓣叶各项动态力学性能最优,所以在对瓣叶的厚度选择时应考虑0.4mm为最佳参考值。通过提取临床CT数据对动脉壁和心脏瓣膜进行三维重建以及动态场分析,可知：最大等效应力、最大主应力和最大剪切应力随在瓣叶厚度方向的变化较明显,这与心脏瓣膜的真实情况相符合。更多还原

【Abstract】 With a rapid aging population the incidence of cardiovascular disease had also increased. Among these disease, valvular heart pathological change is very common in China, which might seriously threaten the life of every patient as well as his/her whole family welfare. Causes of such dysfunctions are mainly considered to be degradation of structure, fatigue failure and valve calcification. Patients in severe condition need timely replacement of heart valves. Bioprosthetic heart valves (BHVs)share similar hemodynamic performance with native valves, both of them have little effects on blood. Compared with other measures, this approach cause less complications even without anticoagulation. But there are several limitations with BHVs, the worst is its durability, under, constant blood flowing accompanied with tissue degradation, calcification and leaflets tear. It is of great significance to find out the failure mechanism of BHVs. Effort to design substitute with great fatigue property are need.In this paper we extracted data from continuous 2D computed tomography (CT)images of heart. A series of preprocess were did with those images including threshold extraction, edit, modify, regional growth and secondary grid generation, arriving at 3D reconstruction of heart valves and aortic vascular. Further optimization was done to get a model precisely described the structure of native heart valves. This is a good resource for finite element analysis after cloud points disposing, polygon process and surface analysis. Information about stress and strain from simulation is a strong supplement of vitro tests.In finite element analysis software package ANSYS Workbench, we did dynamic analysis of BHVs by applying constant pressure to leaflets. Settings such as material properties of blood, leaflets and vessels were all from clinic dada. We could found that leaflets tear are related to maximum stress and the degree of stress focus. The most likely parts to be tore apart are sections showed Max-stress. Actually they were suturing positions of separate leaflet. Generally, the thickness of a single leaflet ranges from 0.25 to 0.5 mm. We define it as a variable, simulations with distinct values showed that the BHVs performed best when its thickness is 0.4 mm, which might be a reference for the choice of thickness to BHVs designers. With 3D models of heart valves and aortic vascular based on CT data, we could gain the maximum equivalent stress, the maximum principal stress and the maximum shear stress change with the thickness of the BHV more obvious. This is a rewarding explore that provides useful reference for optimal design of BHVs design.更多还原