In cardiac biomechanics, people have been developing a complete model of the patient-specific heart. A finite element bi-ventricular model involves several critical steps. First is the acquisition of patient-specific heart geometry. Second is the definition of material model and its constitutive parameters which is suitable to model the behavior of heart muscle. Third is the integration of fiber orientation of myocardium into the bi-ventricular model. The first objective of this study is to investigate some significant aspects in ventricular biomechanics using a simple model of prolate spheroidal left ventricle (LV). These critical aspects include the geometry of LV, the material model, constitutive parameters and fiber orientations. Results of this simplified model are useful in developing a patient-specific model. For example, parametric study of hyper-elastic material is instructive in determining constitutive parameters of myocardium in a patient-specific model. The second objective of this study is to develop a workflow of building a patient-specific bi-ventricular model. It involves working with experimental data like CT images, DTMRI data and so on. A user defined Fung material model is also reviewed in detail. Two methods of assigning fiber orientation are discussed. Finally, the report points out the future work needed to get a valid patient-specific model which can be useful in research and clinical case. / text

Mitral valve disease is widely prevalent among pediatric and adult population across the world, and it encompasses a spectrum of lesions which include congenital valve defects, degenerative valve lesions, and valve dysfunction due to secondary pathologies. Though replacement of the diseased mitral valves with artificial heart valves has been the standard of care until early 1990's, current trends have veered towards complete surgical repair. These trends are encouraging, but current repair techniques are plagued with lack of durability and high rates of failure within 10 years after repair. With increasing number of patients receiving mitral valve repair, there is now an immediate need to understand the mechanisms of repair failure, and assess the role of several clinical risk factors on valve repair. In this thesis, an in vitro pulsatile left heart simulator was developed to mimic the congenital and adult mitral valve pathological morphologies in normal porcine valves, and simulate the pathological valve hemodynamics and mechanics. Different surgical repair techniques were used to correct the valve lesions, and the post repair valve hemodynamics, mechanics and geometry were assessed using quantitative measurement techniques. The extent to which each repair restores physiological valve function and mechanics was assessed, and the impact of different pathological risk factors on repair failure mechanisms was investigated. It is expected that the knowledge from this thesis would play an important role in the evolution of mitral valve surgical repair, and guide the development of more effective and long-lasting heart valve repair technologies.

Ce travail a été réalisé en cotutelle entre l'Université Nationale de Technologie de Ternopil Ivan Pul'uj (TNTU, Ukraine) et l’Université Blaise Pascal (France). Il appartient au domaine scientifique de la biomécanique et de l'informatique. Le but de l'étude est de développer les modèles et les méthodes de traitement des signaux biomécaniques cardiaques par les systèmes de diagnostic assisté par ordinateur avec une précision accrue, informativité et de la complexité de calcul inférieure. La méthode d'analyse statistique du rythme cardiaque a été mise au point. Cette méthode possède une plus grande précision et informativité par rapport aux méthodes connues d'analyse du rythme cardiaque. Dans cette thèse, le logiciel existant de l'analyse des signaux cardiaques biomécaniques a été améliorée par l'ajout de nouveaux modules logiciels, qui mettent en œuvre les nouvelles méthodes de l'analyse du rythme cardiaque et de l'analyse morphologique des signaux cardiaques biomécaniques. / This work has been performed under the co-tutelle agreement between Ternopil Ivan Pul’uj National Technical University in Ternopil (TNTU, Ukraine) and the University Blaise Pascal in Clermont-Ferrand (France). It belongs to the scientific field of biomechanics and informatics. The aim of the study is to develop the mathematical models and methods of the processing of biomechanical heart signals in computer-based diagnostic systems with increased accuracy, informativeness and lower computational complexity. The method of statistical analysis of heart rhythm was developed, which is characterised by higher accuracy and informativeness compared with the known methods of heart rhythm analysis. In this thesis, the existing software of the analysis of biomechanical heart signals was improved by means of adding new software modules that implement the new methods of the analysis of heart rhythm and morphologic analysis of biomechanical heart signals.

<p>  </p> <p>Cardiovascular disease has been the leading cause of death in the United States for over 70 years. To evaluate the extent and progression of cardiovascular disease, non-invasive imaging techniques are frequently used clinically and pre-clinically. Current echocardiographic and cine magnetic resonance approaches rely on measurements that are typically obtained from two-dimensional images, which assumes uniformity of the structure being evaluated. To explore methods to potentially address these shortcomings, our group has developed and validated high frequency four-dimensional ultrasound techniques as well as created a software toolbox that allows for measurement of myocardial kinematics. In this thesis, I assisted in the application of these methods to two murine models of disease states: myocardial infarction and aortic aneurysm. Another study I aided in focused on cardiac magnetic resonance imaging data from patients with Duchenne muscular dystrophy. From our software, we are able to obtain various strain and strain rate estimates that reveal significant functional changes in infarction and Duchenne muscular dystrophy earlier than standard measurement techniques. Furthermore, we are able to identify vascular expansion, transmural thickening, and changes in hemodynamics prior to aneurysm development. Earlier detection and localization allows for more targeted surveillance and interventions, which ultimately may result in improved clinical outcomes. Ideally, these findings can be used to expand the capabilities of cardiac research and the development of clinically applicable imaging techniques and treatments to better address underlying cardiovascular pathophysiology. </p>