Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F18: Biological fluid dynamics: Heart Valves |
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Chair: Wei Sun, Georgia Institute of Technology Room: Georgia World Congress Center B305 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F18.00001: Fluid-structure interaction simulation of transcatheter aortic valve replacement in a patient with bicuspid aortic valve stenosis and mitral regurgitation Wenbin Mao, Andrés Caballero, Tongran Qin, Raymond McKay, Charles Primiano, Susheel Kodali, Wei Sun Transcatheter aortic valve replacement (TAVR) is the standard-of-care treatment for high-risk patients and is also approved for intermediate-risk patients with severe aortic stenosis. However, owing to concerns about valve asymmetry resulting in inadequate expansion or apposition, TAVR in patients with bicuspid aortic valves (BAV) is still considered as a contraindication. Moreover, the effect of TAVR in patients with severe mitral regurgitation (MR) is not clear. Our goal is to investigate the hemodynamic variation in a BAV patient under MR before and after TAVR using fluid-structure interaction (FSI) simulations. A previous validated FSI framework that combines smoothed particle hydrodynamics and nonlinear finite element method is adopted. Results from the pre- and post-TAVR FSI simulations are found to be in good agreement with the clinical data, including velocity waveforms, transvalvular pressure drops, and effective orifice areas. A parametric study is performed to examine the impact of TAV deployment position on the cardiac flow. This study is expected to provide mechanistic insights for TAVR in these clinically challenging cases. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F18.00002: Hemodynamics of Reduced Leaflet Motion in Prosthetic Aortic Valves Jung-Hee Seo, Chi Zhu, Jon Resar, Rajat Mittal Recent clinical studies based on high-resolution computed tomography (CT) scans have shown a higher than expected incidence of reduced leaflet motion (RLM) due to early leaflet thrombosis in bioprosthetic aortic valves. Although in most cases, the RLM is considered subclinical, the hemodynamic impact and long-term clinical significance of RLM are yet understood. In the present study the hemodynamics associated with RLM is investigated in using a sharp-interface immersed boundary based flow-structure-interaction computational modeling. A reduced degree-of-freedom, model for the leaflet dynamics is employed, which accelerated our ability to examine first-order effect of leaflet motion. Simulations for i) normal, ii) RLM in 1, and ii) 2 leaflets are performed to investigate the effect of RLM on the transvalvular hemodynamics and the implication for the progression of disease. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F18.00003: Unsteady forces and vortices of an aortic valve from 3D FSI simulation Haoxiang Luo, Ye Chen There have been a few numerical studies of 3D FSI of the aortic valve, but information about the forces on the valve and the unsteady vortices in the flow is still rare. We developed a 3D FSI model of a bioprosthetic aortic valve and solved the flow using an immersed-boundary method that is parallelized using domain decomposition. The flexible leaflets of the valve were modeled as the hyperelastic Saint Venant-Kirchhoff material and were discretized using 20-node hexahedral elements. The simulation was able to capture both realistic deformation of the leaflets and vortex structures in the flow, thus providing a balanced modeling approach for the flow and the valve. The results show that the pressure distribution on the leaflet surface is highly nonuniform during both opening and closing, and that the jet flow contains a sequence of vortices during the opening process and later experiences significant oscillations. The drag resistance of the valve when it is being pushed open is approximately equivalent to the inertial force of accelerating the fluid column of three diameter length. The “water hammer effect” was also captured, which produces a high peak force on the valve after closure. These details could be potentially used to characterize FSI of the aortic valve. |
Monday, November 19, 2018 8:39AM - 8:52AM |
F18.00004: Modal Decomposition and Lagrangian Coherent Structures Analysis of Flow Past a Dysfunctional Mechanical Aortic Valve Ahmed Darwish, Giuseppe Di Labbio, Wael Saleh, Lyes Kadem Aortic valve replacement is a viable approach in patients with severe aortic stenosis. Patient outcomes are often suboptimal due to valve dysfunction. This is more critical when mechanical heart valves are used where the inherent complexity of the induced flow field gives limited information on the underlying dynamics. Modal decomposition techniques can extract the dominant structures of such a complex flow, by describing an array of driving flow phenomena in just a few modes. Moreover, Finite time Lyapunov exponents (FTLE) are useful to locate Lagrangian coherent structures (LCS) within the flow. In this in vitro work, time-resolved 2D particle image velocimetry was performed in the aorta downstream of a mechanical aortic valve under different configurations of dysfunctions. The underlying coherent dynamics of the flows were extracted using proper orthogonal (POD) and dynamic mode decomposition (DMD). While POD ranks coherent structures based on their energy content, DMD ranks them based on temporal coherence and provide information on the global stability characteristics of the flow. Furthermore, FTLE gives a description of LCS’s dynamics. The results show the ability of these techniques to assess mechanical aortic valve dysfunction and in revealing sub-optimal flow patterns. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F18.00005: Investigating the Hemodynamics of Aortic Stenosis with a Simple Aortic Valve Model Chi Zhu, Jung-Hee Seo, Jon Resar, Rajat Mittal Aortic stenosis, which is caused by the incomplete opening of the aortic valve, is one of the most common valvular diseases. This condition is also known to generate strong systolic murmurs, which contain valuable disease-related information. In the current study, a novel reduced degree-of-freedom leaflet model is employed to investigate post-valvular hemodynamics and leaflet dynamics. This model allows us to examine the hemodynamics of healthy as well as diseased valves in an efficient manner. This simple valve model is shown 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. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F18.00006: Fluid-structure interaction analysis of mitral valve repair with papillary muscle relocation and approximation: a patient-specific analysis Andres Caballero, Wenbin Mao, Raymond McKay, Charles Primiano, Wei Sun Functional mitral regurgitation (FMR) is mainly caused by augmented leaflet tethering resulting from the outward displacement of the papillary muscles (PM). Recently, new subvalvular surgical procedures aiming to reduce leaflet tethering by PM relocation (PMR) and approximation (PMA) have emerged. The purpose of this study was to virtually evaluate the effect of PMA and PMR on left heart (LH) dynamics using a fluid-structure interaction (FSI) modeling approach. Cardiac multi-slice computed tomography images and Doppler echocardiography data from a 71-year-old male patient with severe MR were used to develop and validate a patient-specific 3D LH model. A FSI framework that combines smoothed particle hydrodynamics and nonlinear finite element formulation was used. PMR was simulated by displacing the chordae origins towards the mitral annulus, while PMA was modeled by decreasing the inter-PM distance. Pre- and post-MV repair FSI simulations results were compared, and the effects on cardiac hemodynamics, MR severity, and leaflets deformation state and kinematics were investigated. Results showed that PMR and PMA techniques cause differences in the intraventricular blood flow dynamics and MV mechanics, despite comparable results in restoration of leaflet coaptation and MR reduction. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F18.00007: Jet Vectoring using Asymmetric Prosthetic Heart Valve Design Alexandros Yiannis Rosakis, Chris Roh, Morteza Gharib Previous work has shown that asymmetric nozzle openings can change the direction of the emerging flow. The flow direction can be altered in a similar way through carefully varying the properties of multi-leaflet prosthetic heart valves. The leaflets can be customized by changing their thickness, stiffness, or geometry. We show how altering these leaflet properties affect the opening asymmetry. We further show the effects of resulting asymmetric opening on the flow emerging from the multi-leaflet valve. We expect the capability to control the flow direction in the context of multi-leaflet valve will allow us to develop a patient specific heart valves that can direct the flow most natural to individual patient’s circulatory system. |
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