基于等几何分析的左心室力学行为研究

The heart is one of the most important human organs. The blood circulation system completes substance transportation and metabolic functions by means of its pump blood function. Heart diseases and cardiovascular diseases have now become the highest incidence of serious diseases in western industrialized countries. In China, these diseases have already occupied the top of the main disease mortality of urban and rural residents, so they are the number one killer to human health. The huge costs of treatment of these diseases have become a heavy burden on the family, society and country. Mechanical properties of myocardial tissue have a substantial effect on heart pump function. Therefore, to grasp the mechanical behavior and property of myocardial tissue play a key role on a thorough understanding of the heart organ normal physiological functions and pathological mechanism of various pathological circumstances. Study on mechanical behavior of the left ventricular, reveal the mechanism of physiological phenomena from a biomechanical view, provide an effective method for clinical diagnosis and treatment of medical, to realize effective early warning against cardiovascular disease, diagnosis and treatment, has become the hot spot of basic and clinical research. Currently, there are still many deficiencies in research work about cardiac biomechanics. The main deficiencies are as follow: (1) the lack of accurate and appropriate constitutive modeling of myocardial tissue; (2) the lack of efficient and reliable numerical simulation method; (3) the lack of accurate and efficient build method for cardiac models based on cardiac anatomy and physiology structure. It is an important frontier development direction of cardiovascular biomechanics and urgent demand to provide for patient-specific comprehensive biomechanical analysis and specific treatment planning. In order to respond to this need, we must find effective solutions to the above main deficiencies in current research work about cardiac biomechanics. In this research project, we adopt the latest myocardial constitutive model proposed by Holzapfel and Ogden based on the myocardium locally orthotropic mirco-structure, and firstly use a new numerical simulation method - isogeometric analysis method, study on mechanical behavior of the left ventricular under normal physiological and various pathological circumstances. We will provide the efficient build method for complex three-dimensional cardiac models with isogeometric analysis, reveal and assess the main factors that impact mechanical behavior of the left ventricular, put forward a reasonable evaluation method that reflects the loss of pump blood function of the left ventricular under pathological conditions.

心肌组织的力学性能对心脏泵血功能有着实质性影响，因此研究左心室力学行为，从生物力学角度揭示相关生理和病理现象的机理，对最终实现对心血管疾病进行有效预警、诊断和防治具有重要的实际意义。心脏研究当前仍存在许多不足，主要体现在缺乏准确适用的心肌本构模型、缺乏高效可靠的数值计算方法、缺乏精确快捷的心脏结构建模方法等方面，提供针对个体特异性的全面深入的生物力学分析和特定治疗方案是心血管生物力学一个重要前沿发展方向和迫切需求。为了有效应对这一需求，必须对上述不足寻求有效的解决方案。本项目采用Holzapfel和Ogden 最新提出的基于心肌微观结构特征的心肌本构模型，同时首次引入一种新的数值计算方法-等几何分析方法，研究人体左心室在正常及病理情况下的力学行为特征，提出适用于心脏三维复杂模型的等几何分析建模方法，揭示和评估影响左心室力学行为的主要因素，提出病理情况下反映左心室力学性能损失的合理评估方法。

根据世界卫生组织(WHO)统计，每年死于心血管系统疾病的人数约占到全球死亡人数的三分之一。在国内，心脏病和脑血管疾病已占据城乡居民主要疾病死亡率的首位，且呈逐年上升趋势，治疗的巨额费用已成为家庭、社会和国家的沉重负担。人类健康与疾病的生物学基础和心脑血管疾病等非传染疾病防治是国家的重大战略需求问题。从生物力学角度揭示心脏相关生理现象的机理，为医学临床诊断和治疗提供有效的指导，对最终实现对心血管疾病进行有效预警、诊断和防治等具有重要的实际意义。. 本项目基于一种新的数值计算方法—等几何分析方法，提出了适用于心脏三维复杂模型的等几何分析建模方法，研究了人体左心室在正常及病理情况下的力学行为特征，揭示和评估影响左心室力学行为的主要因素，主要结果如下：.（1）采用优化算法确定了Holzapfel–Ogden 本构模型中8个材料参数，建立了本构方程具体形式，预测结果与实验结果一致。定量讨论了本构模型材料参数变化对数值分析结果的影响，发现较小的材料参数差异并不导致左心室应力应变状态发生较大的改变，这一结论对指导心肌组织实验结果的优化处理具有较大的应用价值。研究发现同一问题采用不同本构模型计算所得到的左心室应力应变状态有很大的差异，表明左心室收缩舒张过程具有很强的几何与材料非线性，合理准确的心肌本构模型是研究人体左心室非线性力学行为的关键。.（2）基于MRI图像，采用B样条曲面拟合算法和基于规则的心肌纤维生成算法建立了人体左心室结构模型，能精确反映心肌纤维的结构分布特征。研究发现心肌纤维空间分布变化对左心室应力应变状态有极大影响，特别是在病理情况下，这一研究发现可为医学影像学的临床诊断提供理论依据和指导。.（3）研究了人体左心室舒张期末压力体积关系，发现与人体心脏实验测试结果吻合很好，表明本课题研究建立的计算模型通过结合特定个体的心室结构特征和材料属性参数，可用于预测左心室压力—体积变化规律，为临床诊断提供辅助和指导。