Dynamic Simulation of Bioprosthetic Heart Valves Using a Stress Resultant Shell Model

It is a widely accepted axiom that localized concentration of mechanical stress and large flexural deformation is closely related to the calcification and tissue degeneration in bioprosthetic heart valves (BHV). In order to investigate the complex BHV deformations and stress distributions throughout the cardiac cycle, it is necessary to perform an accurate dynamic analysis with a morphologically and physiologically realistic material specification for the leaflets. We have developed a stress resultant shell model for BHV leaflets incorporating a Fung-elastic constitutive model for in-plane and bending responses separately. Validation studies were performed by comparing the finite element predicted displacement and strain measures with the experimentally measured data under physiological pressure loads. Computed regions of stress concentration and large flexural deformation during the opening and closing phases of the cardiac cycle correlated with previously reported regions of calcification and/or mechanical damage on BHV leaflets. It is expected that the developed experimental and computational methodology will aid in the understanding of the complex dynamic behavior of native and bioprosthetic valves and in the development of tissue engineered valve substitutes.     

用三维重建和有限元方法对人体心脏进行力学分析

目的　建立人体心脏的三维几何模型和有限元网格模型，进行有限元仿真计算。方法　利用可视化人体心脏数据集，通过3D-DOCTOR软件和SOLIDWORKS软件重建心脏外形和内腔的三维结构数据，以STEP格式导入ABAQUS有限元软件形成网格模型。在有限元网格模型的基础上进行心脏自振频率、内腔血压等载荷情况下的力学性能分析。结果　建立了一个数字化心脏可视模型。能够反映心脏三维形状和内腔结构；得到了心脏内腔的大致容积；反映了心脏心肌不同区域的不同性质；得到了心脏3个方向的自振频率和振型，以及内腔血压下的应力分布。结论　建立了可视化三维心脏的几何和网格模型，反映了心脏的外形和内腔。利用有限元分析方法，能够为心脏的生物力学分析提供可视化的数值仿真平台。     

A Dynamic Heart System to Facilitate the Development of Mitral Valve Repair Techniques

Objective: The development of a novel surgical tool or technique for mitral valve repair can be hampered by cost, complexity, and time associated with performing animal trials. A dynamically pressurized model was developed to control pressure and flowrate profiles in intact porcine hearts in order to quantify mitral regurgitation and evaluate the quality of mitral valve repair. Methods: A pulse duplication system was designed to replicate physiological conditions in explanted hearts. To test the capabilities of this system in measuring varying degrees of mitral regurgitation, the output of eight porcine hearts was measured for two different pressure waveforms before and after induced mitral valve failure. Four hearts were further repaired and tested. Measurements were compared with echocardiographic images. Results: For all trials, cardiac output decreased as left ventricular pressure was increased. After induction of mitral valve insufficiencies, cardiac output decreased, with a peak regurgitant fraction of 71.8%. Echocardiography clearly showed increases in regurgitant severity from post-valve failure and with increased pressure. Conclusions: The dynamic heart model consistently and reliably quantifies mitral regurgitation across a range of severities. Advantages include low experimental cost and time associated with each trial, while still allowing for surgical evaluations in an intact heart.     

基于小波逆变换合成的心率变异性信号的IPFM模型

本文提出了心率变异性信号的一种改进的积分脉冲频率调制的计算机仿真模型。由于合理地设计了模型的前置部分，从而使得仿真的ＨＲＶ信号的频谱和调制信号的频谱具有一致性。又由于采用小波逆变换的方法合成了ＨＲＶ信号中的１／ｆ部分，从而使得仿真的ＨＲＶ信号的时特征及频域特征均比原有的ＩＰＦＭ模型更近近于实际的ＨＲＶ信号。     

有限元法在脊柱生物力学应用中的新进展

本文归纳整理了近3年来使用有限元分析方法研究脊柱生物力学的主要工作,总结了有限元建模方法在建立微观结构以更细致化、常见椎骨参数权重的个性化研究、采用新标定校准和赋值方法使模型更准确化、自动化分网赋值方法4个方面的发展,及其在植入器械设计评估、椎间盘生物力学、异常脊柱结构生物力学、动态仿真4个脊柱生物力学应用方向的主要研究进展。并结合最新的研究趋势,对有限元法在创伤机理研究、手术模拟、新药评估等方面的应用前景进行展望。     

封面

本文归纳整理了近3年来使用有限元分析方法研究脊柱生物力学的主要工作,总结了有限元建模方法在建立微观结构以更细致化、常见椎骨参数权重的个性化研究、采用新标定校准和赋值方法使模型更准确化、自动化分网赋值方法4个方面的发展,及其在植入器械设计评估、椎间盘生物力学、异常脊柱结构生物力学、动态仿真4个脊柱生物力学应用方向的主要研究进展。并结合最新的研究趋势,对有限元法在创伤机理研究、手术模拟、新药评估等方面的应用前景进行展望。     

Computational Model for Early Cardiac Looping

Looping is a vital event during early cardiac morphogenesis, as the initially straight heart tube bends and twists into a curved tube, laying out the basic pattern of the future four-chambered heart. Despite intensive study for almost a century, the biophysical mechanisms that drive this process are not well understood. To explore a recently proposed hypothesis for looping, we constructed a finite element model for the embryonic chick heart during the first phase of looping, called c-looping. The model includes the main structures of the early heart (heart tube, omphalomesenteric veins, and dorsal mesocardium), and the analysis features realistic three-dimensional geometry, nonlinear passive and active material properties, and anisotropic growth. As per our earlier hypothesis for c-looping, actin-based morpho-genetic processes (active cell shape change, cytoskeletal contraction, and cell migration) are simulated in specific regions of the model. The model correctly predicts the initial gross morphological shape changes of the heart, as well as distributions of morphogenetic stresses and strains measured in embryonic chick hearts. The model was tested further in studies that perturbed normal cardiac morphogenesis. The model, taken together with the new experimental data, supports our hypothesis for the mechanisms that drive early looping.Originaly published Online First May 27, 2006, DOI: . Due to a typesetting error, this article was originally published online in an uncorrected form. The corrected article is reprinted in its entirety here.     

Three-Dimensional Stress and Strain in Passive Rabbit Left Ventricle: A Model Study

To determine regional stress and strain distributions in rabbit ventricular myocardium, an anatomically detailed finite element model was used to solve the equations of stress equilibrium during passive filling of the left ventricle. Computations were conducted on a scalable parallel processing computer and performance was found to scale well with the number of processors used, so that stimulations previously requiring approximately 60 min were completed in just over 5 min. Epicardial strains from the model analysis showed good agreement (RMSE=0.007332) with experimental measurements when material properties were chosen such that cross fiber strain was more heterogeneous than fiber strain, which is also consistent with experimental observations in other species. © 2000 Biomedical Engineering Society. PAC00: 8719Hh, 8719Rr, 8710+e     

化学突触短时程可塑性的动态模型及计算机仿真

提出了化学突触短时程可塑性的动态模型，此模型以神经生物学为依据，通过计算机模拟，较好地反映了突触短时程可塑性的动态特性，再现了突触的易化、压抑、增强，恢复到正常水平的动态过程。     

三维颅骨模型的建立和有限元及实验应力分析的研究

观察颅骨表面的应力分布情况,探索快速建立完整颅骨三维模型并进行有限元分析的方法。取两具新鲜颅骨进行多层螺旋CT扫描,利用专业医学建模软件完成三维重建,并将生成的三维模型导入ANSYS中进行有限元分析。用电测法测试撞击时颅骨表面的应变情况,运用实验应力分析的理论,得到了颅骨表面主应力的大小。为临床提供一定的理论依据。     

基于动态心脏模型的体表心电图仿真研究

以往的电生理心脏模型大多是静态的,而非动态模型.这样在用准静电场理论求解体表电位时,整个心动周期中等效心电偶极子（源点）与体表（场点）之间的距离假设为恒定不变,从而会引入较大的系统误差.因此,为了更准确仿真心电图,有必要采用动态或跳动的心脏模型.基于原来静态心脏模型,构造了一个动态心脏模型,并对体表12导联心电图进行仿真比较研究.在动态心脏模型中考虑了心肌电兴奋引起的心脏机械力学收缩,通过计算心动周期中心室壁的位移,从而将心脏与体表之间的相对距离变化考虑进体表电位计算过程.仿真结果表明,对于正常心电图,基于动态心脏模型的仿真结果比基于静态心脏模型的仿真结果更符合临床记录心电图,特别是V1-V6胸导联的ST段和T波.对于前壁轻微缺血情况,在动态心脏模型的仿真心电图中能明显看出ST段和T波的变化,而在静态心脏模型的仿真心电图中与正常心电图相比看不出什么变化.本研究的仿真研究证实了动态心脏模型的确能更准确地仿真体表心电图.     

人在摔倒时股骨上端承载能力的有限元分析——(I)有限元分析模型及股骨失效准则的建立

摔跤后,骨折已成为老年人最严重的损伤之一。有限元分析被证实在股骨的结构分析中是一项非常有用的工具。我们建立了股骨上端的有限元模型,并基于有关文献中关于股骨密质骨和松质骨的强度实验数据建立了Hoffm an失效准则。有限元模型和失效准则用前人的实验结果进行了验证。结果表明:预测的松质骨失效载荷仅比实验值低0.5%,而密质骨失效载荷仅比实验值高4.2%。这说明我们建立的有限元模型结合Hoffm an失效准则将很好地预测人摔倒时股骨的承载能力。     

个性化舌侧自锁矫治器咬合过程瞬态动力学分析及优化

目的 研究瞬态咬合力作用下个性化舌侧自锁矫治器的应力分布特点,并以此为基础对其进行优化。方法 采用CT扫描、逆向工程和计算机辅助设计技术构建全牙列、个性化舌侧矫治器及弓丝的整体三维模型,对其进行咬合过程的瞬态动态动力学非线性分析及优化设计,并通过制造出优化后的舌侧矫治器进行试验研究,验证有限元模型的可靠性。结果 托槽底板处产生的等效应力均要大于托槽体上其他部位的应力;通过在托槽盖上设置加强筋,使得托槽盖的最大等效应力降低了60.9%,避免了弓丝与托槽盖作用时过大的应力集中;托槽盖加载试验结果与模拟结果基本吻合。结论 临床进行舌侧正畸时,应关注咬合力作用点与矫治器的相对位置,避免影响矫治器的自锁性能;通过对矫治器进行优化,可将弓丝的弹性势能更加有效地传递到牙齿上,减少正畸力的损耗。     

不同重建工况下Forsus前导下颌后髁突应力、位移的分布变化

目的仿真分析不同工况下推杆式矫治器(Forsus)前导下颌后髁突应力、位移的分布变化,为Forsus临床应用提供参考。方法经Abaqus6.5软件构建Forsus前导下颌三维有限元模型,模拟下颌水平前伸距离分别为3、4、5、6、7 mm,对应下颌垂直打开距离为4、3.5、3、2.5、2 mm的5种重建工况,分析"下颌骨-颞下颌关节"的应力、位移变化和旋转趋势,以评估髁突生长改建的重建方式。结果 5种工况下,最大应力分布在下颌骨髁突、乙状切迹区和髁突颈后份区域。随下颌水平前导的位移量增加,髁突乙状切迹区和髁突颈后份区域应力较缓增大,但仍处于相同数量级(30 MPa);髁突区域应力分布较稳定且没有明显的应力集中。从工况1～5髁突水平方向位移逐渐增大,方向皆向前;髁突垂直向位移平均值也逐渐增大,方向皆向下;下颌骨直接拉伸到指定重建位置时,髁突运动方向也为前下。结论生理性咬合重建的范围,不同程度地前导下颌不会改变髁突软骨附近的应力分布趋势。考虑颞下颌关节生理承受性,严重下颌后缩时可分段前伸以利于髁突生长改建。     

可实现特殊网格划分的个性化动脉瘤实体模型的构建

目的　通过建立一个可以用于有限元分析,可进行分区域网格划分的个性化主动脉弓动脉瘤实体模型,探索一种能满足特殊网格划分要求的个性化实体模型的建立方法。方法　采用逆向工程的思想方法,借助Geomagic和Pro/E软件,以原始STL格式的表面模型为依据,建立了一个个性化主动脉弓动脉瘤实体模型,并加入理想化支架模型,导入ANSYS有限元分析软件最终完成实体模型的建立和分块。结果　建立的有限元模型,可进行针对边界层和支架的分区域网格划分,并完成了一个血流动力学模拟仿真。结论　建立的模型基本满足对特定区域网格细划分的需要,可以为支架介入治疗动脉瘤的血流动力学仿真提供基础。所建模型的方法是可行的,可以为将来建立其他类似模型提供参考。     

Kubicek每搏心输出量计算公式的三维有限元仿真研究

我们从 Kubicek模型三维有限元仿真的角度对 Kubicek每搏心输出量计算公式的临床应用价值进行了研究。在计算机仿真研究中 ,我们对比了模型仿真结果、具体采用 Kubicek每搏心输出量计算公式所得结果以及所设模型的理论计算结果。仿真结果表明 :模型中阻抗改变与主动脉中血液容积改变之间存在着近似的线性关系 ,证明了 Kubicek每搏心输出量计算公式具有一定的临床应用价值 ,同时也为心阻抗血流图基础理论提供了新的研究途径。     

精细乳腺有限元模型温度场的仿真与临床验证

为了研究乳腺肿瘤对体表温度分布的影响,本研究基于乳腺解剖学结构和生理学特征,建立了适合乳腺温度场分析的精细乳腺三维有限元模型。与传统乳腺模型相比,该模型更接近乳房生理结构,因此能更加准确的仿真出正常和嵌合肿瘤的乳腺温度场分布。本研究分别对传统均匀结构乳腺模型、正常精细结构乳腺模型和嵌合肿瘤精细乳腺模型进行了温度场分析,并与临床医学病例中的乳腺肿瘤热像图对比,发现结果吻合得很好。研究结果为乳腺癌的热成像检测提供了重要的参考依据。     

灌流式生物反应器内支架材料孔隙流场和壁面剪应力的数值分析

为获得支架材料孔隙受到的壁面剪应力的大小及分布、孔隙内压力分布以及支架材料与灌流小室之间不同缝隙时的灌流率。根据有限元方法建立了灌流式生物反应器小室内3种支架材料孔隙模型，用ansys软件分析了各种模型在不同工况下的灌流情况。结果表明，支架材料与灌流小室之间的孔隙决定灌流率，缝隙大于0.5mm时灌流率小于60％；支架材料孔隙壁面剪应力大小主要受灌流流量的影响，调节灌流流量是控制剪应力水平的主要手段。孔壁剪应力和孔内流体压力的分布均由支架材料孔隙的形状特征所决定。     

基于无网格的软组织切割模型的研究进展

具备支持实时交互能力的软组织切割模型对于虚拟手术仿真系统具有至关重要的意义。传统的软组织切割模型多基于网格建立,将软组织切割过程建模为手术刀具与软组织几何模型之间的网格切割计算,并在此基础上建立和求解生物力学方程以描述切割过程。由于网格切割计算代价高且软组织切割过程中涉及到复杂的生物力学问题,很难实现实时交互,严重影响了虚拟手术仿真效果。与此相反,基于无网格的软组织切割模型打破了网格限制,在触觉/视觉逼真度和实时性方面都具有很大优势。文中从力反馈和视觉反馈的渲染质量和速度等方面,就基于无网格的软组织切割模型的研究现状进行了概述,对存在的问题进行了分析和总结,并对未来的发展方向进行展望。     

Finite element analysis of the middle ear transfer functions and related pathologies

With developments in software and micro-measurement technology, a three-dimensional middle ear finite element (FE) model can now be more easily constructed to study sound transfer function. Many FE models of the middle ear have been constructed to date, and each has its own particular advantages and disadvantages. In this article, we review the latest developments and technologies in the field of the FE models of the middle ear, and the use of FE in the study of middle ear pathology. Proposals are made for future developments in the field of finite element analysis of middle ear transfer function.