HIGH-FIDELITY COMPUTATIONAL MODELING OF THE COUPLED FLOW-ACOUSTIC PHYSICS OF HEART MURMURS

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Date
2018-08-20
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Johns Hopkins University
Abstract
Cardiac auscultation with a stethoscope has served as the primary method for qualitative screening of cardiovascular conditions for over a century. However, a lack of quantitative understanding of the flow mechanism(s) responsible for the generation of the murmurs and the effect of intervening tissues on the propagation of these murmurs has been a significant limiting factor in the advancement of automated cardiac auscultation. In this study, a multiphysics computational modeling approach is used to investigate these issues. A previously developed sharp-interface immersed boundary flow solver is upgraded to efficiently tackle internal flow problems which are commonly seen in cardiovascular systems. First, the geometric multigrid pressure Poisson solver is replaced by an efficient biconjugate gradient stabilized method. Second, a graph-partitioning based parallel framework is adopted to reduce computational overhead associated with the large proportion of wasted grid points in internal flow problems. To understand the role of the shear wave in the propagation of murmurs, a two-dimensional hemodynamic-acoustic study is conducted, wherein a classic vector decomposition is employed to separate the murmurs generated from an arterial stenosis into compression part and shear part. Results show that the shear wave has a profound impact on source localization and signal characteristics. Next, we use a one-way coupled hemodynamic-acoustic approach to investigate the generation and propagation of murmurs associated with the aortic stenosis from first principles. Direct numerical simulation is used to explore the hemodynamics of the post-stenotic jets. Subsequently, the propagation of the murmurs through a tissue-like material is resolved by a high-order, linear viscoelastic wave solver. The implications of these results for cardiac auscultation are discussed. Finally, the effect of the valve on the murmur generation is explored. The fluid-structure interaction between the valve and the flow is modeled through a reduced degree-of-freedom model of the aortic valve. Aortic stenoses with different severities are created by changing the stiffness of the leaflets. This simple valve model is demonstrated to be able to accurately capture the opening/closing motion predicted by a more sophisticated model. Simulations with the aortic valve model provide additional insights into post-valvular flow and the characteristics of the murmur source.
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Keywords
Heart sound, Cardiovascular flow, Immersed boundary method, Hemodynamics, Elastic waves, Systolic murmur, Heart valves, Flow structure interaction, High performance computing, Direct numerical simulation
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