Myocardium Biomechanical Modelling and Myocardial Contraction Force Reconstruction

心肌（心脏肌肉）的计算模型，特别是左心室（LV），是研究其力学和深入了解其生理学的有效工具。与身体的许多其他组织不同，跳动的心脏是主动和被动的，主动成分产生由心脏电生理引起的协调的肌肉收缩，而被动成分则对外力和自身产生的收缩作出反应。结合组织复杂的内在特性，有效成分的复杂性及其与心脏电生理活动的耦合使得开发可靠的模型非常具有挑战性。在过去的几十年里，研究人员开发了各种复杂程度的计算心脏模型，从简单的被动线性弹性各向同性模型到高度复杂的被动/主动超弹性各向异性模型。虽然后一种模型很有希望，因为它们与实验数据相当吻合，但它们通常基于非常复杂的算法，使得其开发成为一项艰巨的任务，需要耗费大量的时间和资源。此外，目前还没有商业软件能够模拟心脏跳动机制的主动/被动组件。这些计算工具的可用性非常有限，阻碍了心脏力学研究的加速进展，并最终影响了了解心肌力学及其生理学急需的有效工具的发展。从工程角度解决这一问题的一个潜在解决方案是开发一种新的范式，该范式能够使用传统的有限元（FE）公式开发计算心脏力学模型，从而将商业有限元软件引擎和模块集成到软件包中，用于研究心脏力学。我们建议通过开发一种基于新范式的新的有限元公式来解决当前心脏力学模型的局限性。这种模式使得商业有限元软件引擎和模块的应用成为可能，从而开发出高精度的心脏力学仿真软件工具。该模型将心肌理想化为一种复合材料，肌纤维被复杂的背景包围，模仿组织细胞外基质。心脏跳动的肌纤维将被建模为具有已知时间变化预应力的超弹性预应力棒。细胞外基质将被理想化为一种超弹性材料，与它的多组分的已知力学特性相一致。开发的模型将使用实验推导的测量值进行测试。将其作为收缩力重构逆问题框架中的正演模型。这些力将利用成像得到的收缩位移数据进行重建。这些力可用于进一步了解各种病理（例如与心律失常和心肌梗死相关的病理）。最后，将建立机电耦合模型，其中将纳入已开发的心脏力学有限元模型。所建立的正演模型和反演模型可用于进一步了解心脏跳动的力学。它们可以在解决关于心脏生理学的广泛基础科学问题和深入了解病理条件的途径方面发挥重要作用。例如，它们可以应用于充血性心力衰竭患者心脏再同步化治疗的计算机模拟。这种模拟可以测试各种治疗方案，为实现最佳结果铺平道路。

Computational models of the myocardium (heart muscle), in particular the left ventricle (LV), are effective tools that can be used to study its mechanics and to gain insight into its physiology. Unlike many other tissues in the body, the beating heart is both active and passive such that the active component generates coordinated muscle contraction resulting from the heart's electrophysiology while its passive component responds to external forces and its own generated contraction. Combined with the tissue complex intrinsic properties, the complexity of the active component and its coupling with the heart's electrophysiological activity has made developing reliable models very challenging. Over the last many decades, researchers have developed computational cardiac models with various levels of sophistication ranging from simple passive linear elastic isotropic models to highly complex passive/active hyperelastic anisotropic models. While the latter models are promising as they agree reasonably well with experimental data they are often based on very complex algorithms, rendering its development a daunting task that require demanding time and resources. Furthermore, no commercial software is available that is capable of simulating the active/passive components of the beating heart mechanics. The very limited availability of such computational tools has prevented accelerated progress in studying cardiac mechanics and ultimately impacting the development of much needed effective tools to understand the myocardium mechanics and its physiology. One potential solution to address this issue from an engineering perspective is to develop a novel paradigm which enables developing computational cardiac mechanics models using traditional Finite Elements (FE) formulation such that commercial FE software engine and modules are integrated into a software package to be used for studying cardiac mechanics. We propose to address the limitations of current cardiac mechanics models by developing a new FE formulation based on a novel paradigm. This paradigm makes possible the utility of commercial FE software engine and modules for cardiac mechanics model development to develop highly accurate software tool for cardiac mechanics simulation. This model idealizes the myocardium as a composite material with myofibers surrounded by a complex background that mimics the tissue extracellular matrix. The myofibers of the beating heart will be modeled as hyperelastic prestressed rods with known time varying prestress. The extracellular matrix will be idealized as a hyperelastic material consistent with known mechanical properties of its multi constituents. The developed model will be tested using experimentally-derived measurements. It will be used as forward model in an inverse problem framework for contraction force reconstruction. These forces will be reconstructed using contraction displacement data derived from imaging. These forces can be used to further understand various pathologies (e.g. pathologies associated with arrhythmia and myocardial infarction). Finally, electromechanical coupling model will be developed where the developed FE model of the cardiac mechanics will be incorporated. The developed forward and inverse models can be used for furthering our understanding of the beating heart mechanics. They can play an important role in addressing a wide range of fundamental scientific questions regarding the heart physiology and gaining insight into pathways of pathological conditions. For example, they can be applied in computer simulation of cardiac resynchronization therapy used to treat patients with congestive heart failure. This simulation enables testing various therapy scenarios, paving the way for achieving optimal outcome.