心室电学—力学复合模型初步建模仿真研究

【作者】 霍梅梅；

【导师】 夏灵；

【作者基本信息】 浙江大学 ， 生物医学工程， 2003， 硕士

【摘要】 计算机心脏仿真模型是应用计算机强有力的计算能力、图形显示能力将活体心脏所具有的动态心电兴奋传播、心肌收缩、瓣膜振动和血液流动等过程赋予仿真模型，并使其从形态、运动和功能等方面都逼真地再现出来，便于人们对心脏生理、病理的研究。其中，心脏的心电活动和心肌力学特性及其相互影响是当前心脏模型研究的主流。浙江大学生物医学工程研究所的科研人员在吕维雪教授的带领下，开发出了具有国际先进水平的心脏电生理模型LFX，通过该模型可以得到人体的心电兴奋序列和其它各种生物电活动特性。但是该模型只仿真了静态情况下的心电特性。基于这一模型，刘峰博士等人建立了考虑心电特性的左心室力学模型，对心脏的电生理模型和力学模型的结合进行了初步的研究。在前人所做工作的基础上，本文建立了考虑偶极子在心动周期中位移的双心室模型，从而使原来静态的心脏获得活力，跳动起来。进而我们“测算”了人体的12导联心电图以及心脏跳动过程中心室壁的变形。本文首先采用有限元方法，充分考虑了心肌的纤维旋向，将心室划分为若干个单元，然后提取有限元节点的兴奋时序，并采用等参元理论和复合材料理论，计算得到心电信号激励产生的心肌收缩力，并由此计算心电偶极子在心动周期中的位移。得到偶极子的位移后，采用LFX模型中的边界元方法计算得到12导联心电图。利用等参逆变换我们可以计算心室内任意材料点的位移，用来分析心壁的运动和变形。我们采用了位移、应变、扭转角度等参数来描述心室壁的运动变形情况。分析结果显示：(1)12导联心电图的ST—T段明显比原来LFX模型有了较大的改善；(2)在收缩期，右心室自由壁向着室间隔位移，同时自由壁的心底和心中部向着心尖位移，右心室室腔缩小；最小主应变E3在右心室自由壁心内膜的分布在心尖最大，其次是中部，方向基本上与纤维旋向一致。(3)在收缩期，左心室心壁不同部位有着不同程度的增厚：心底和心中部向着心尖位移，心尖位移最小，基本不动，自由壁向着室间隔位移；心壁沿着左心室长轴方向存在着扭 刘以 摘要 浙江大学硕士毕业论文转，扭转角度在心尖最大；最小主应变E3在右心室中壁的分布沿着长轴方向向着心尖增大，E3的方向与纤维旋向基本一致。最后我们将仿真得到的数据与采用医学成像技术得到的结果以及其它模型的结果进行了对比分析，证明我们的模型及其精度达到了预期的目的。 综上所述，本文建立的模型主要探讨了心电激励导致的心壁的位移和应变以及心壁的位移反过来对心电兴奋传播的影响。目前国际上复合心脏建模研究中，学者们都在积极努力把心脏的电学特性和力学特性结合起来，但是既能仿真心电图又能分析心壁运动特性的模型目前还没有看到有文献报道。我们的仿真实践证明，这样构建的虚拟心脏模型为深入研究心脏的临床生理病理现象提供了行之有效的和无创性的研究方法和思路。更多还原

【Abstract】 The computer heart model is the one combining transmission procedure of heart electric stimulus, myocardial contraction, valve vibration, blood flow and other physiological properties of the in vivo heart. Using the powerful computational ability and image processing ability of computer, the model should reproduce the shape, motion and function of human heart, so as to make it possible to better evaluate mechanical, electrical, and physio-pathological properties of the heart. At present, the important things in modeling heart are bioelectrical activity, myocardial mechanical property and their coupling problems.Leaded by professor Lu Weixue, the researchers in Biomedical Institute of Zhejiang University have developed an electrical model, LFX. Using this model, we can get the excitation series and other bioelectrical properties of the in vivo heart. Based on the model LFX, Dr. Liu has constructed a three-dimensional finite element mechanical model of left ventricle, which included the electrical properties of the heart. Liu made an attempt to combine the electrical model and mechanical model of the heart. Based on the previous work, in this article the author has established a biventricular model including the displacements of cardiac dipoles during the period of the systole of heart, which made the previous static heart get energy and can beat. Finally the 12-lead ECG was calculated and the motion and deformation of the ventricular wall were analyzed.Firstly, on the basis of considering the fiber orientation of ventricles fully, the two ventricles were segmented into a number of finite elements by using of FEM. Secondly, normal cardioelectrical excitation series was read from LFX model simulation. Thirdly, the active forces per finite element at different time during the period of systole of the heart were calculated by means of isoparametric theory and composite theory, and also the displacements of cardiac dipoles during the period of systole was calculated. Finally, we simulated the 12-lead ECG and some parametersto describe the motion and deformation of ventricular wall, such as displacement, strain, torsion angle and so on.The simulation results show that: (1) The ST-T of the 12-lead ECG has a reasonable improvement than the previous LFX model; (2) During the period of systole, the right ventricular free wall moves towards septum, and at the same time, the base and middle of the free wall move towards apex, which make the volume of right ventricle smaller; the minimum principle strain E3 is biggest at the apex, then at the middle of free wall, and its direction is in the approximate direction of the epicardial muscle fibers. (3) During the period of systole, left ventricular wall has different degrees of thickness at different material point; the base and middle of the left ventricular free wall move towards the apex and the apex remains almost static; torsion angle, which describe the torsion of wall along the long axis of left ventricle, is biggest at the apex; the minimum principle strain E3 is biggest at apex and its direction on the surface of middle wall of left ventricle is in the approximate direction of fiber orientation. The results were compared with solutions obtained from MR tagging images and those from other models, and it proved that the model and its precision had attained the expected ,goal.In a word, the model established by the work of this article mainly investigated the motion and deformation caused by the cardioelectrical excitation and the influence to cardioelectrical excitation transmission caused by the displacements of ventricular wall. In the international cardiac research area, many researchers are throwing themselves into the work that combine the electrical and mechanical properties of biventricle. But at present, there are no literature reported the ECG and motion analysis of ventricles at the same time. It proved that our virtual biventricular model has provided an effective and noninvasive method to investigate the physio-pathological properties of the hear更多还原