Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P23: Biological Fluid Dynamics : Cardiac Flows II |
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Chair: Amir Arzani, Northern Arizona University Room: 605 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P23.00001: In-vitro investigation of the effect of variable pulsatile flow and Left Ventricular Assist Device speed on the intraventricular hemodynamics Marissa Miramontes, Fanette Chassagne, Venkat Keshav Chivukula, Jennifer Beckman, Claudius Mahr, Alberto Aliseda Left Ventricular Assist Devices (LVAD) are used to treat end-stage heart failure but induce unfavorable hemodynamics in the left ventricle (LV) that can result in thromboembolic and hemorrhagic events such as stroke. This study aims to quantify the impact of native contractility and LVAD speed on fluid mechanics inside the LV, and the associated thrombogenicity. Stereo Particle Image Velocimetry (PIV) measurements of the flow in a patient-specific LV flow phantom implanted with a real LVAD are analyzed under a wide range of clinically relevant parameters: pulsatility, preload and afterload. The combination of reduced pulsatility and LVAD speed results in highly heterogenous flow patterns, with co-existing jet-like flow and high-residence time recirculating regions. Increased pulsatile flow and higher LVAD speeds improve velocity field variability, associated with less stagnation. Pulsatility plays a greater role in reducing stagnant regions compared to increasing LVAD speed. Unfavorable hemodynamics caused by decreased contractility combined with low LVAD speed may explain the persistent incidence of thrombosis even in new generation LVADs. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P23.00002: Numerical Modeling of Thrombus Transport to the Cerebral Vasculature in the Presence of a Left Ventricular Assist Device Angela Straccia, Venkat Keshav Chivukula, Fanette Chassagne, Jennifer Beckman, Claudius Mahr, Alberto Aliseda Left ventricular assist devices (LVAD) represent an increasingly available treatment for end-stage heart failure. Despite improvements in LVAD design that have greatly reduced the incidence of in-pump thrombosis, thromboembolic events, such as stroke, remain the main cause of mortality and morbidity. This study aims to identify the relationship between the source of thrombi -- LVAD outflow graft or aortic valve -- and their destination in the cerebral vasculature. The hemodynamics, from the aortic arch and LVAD outflow graft to the Circle of Willis, are investigated using 3D time-resolved computational fluid dynamics (CFD) in patient-specific models obtained from segmented medical imaging. Thrombi of different sizes are seeded in the blood flow and followed throughout their trajectories via Lagrangian particle tracking, accounting for inertial effects. We achieve a statistical description of the likelihood of thrombi being transported towards different regions of the cerebral circulation by studying a wide distribution of thrombi properties and seeding locations. Patient-specific stroke risk, and its origins, is quantified, along with the altered hemodynamics in the cerebral vasculature in the presence of stroke. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P23.00003: Further classification of the cardiac vortex: On the scaling of core vorticity with heart rate Giuseppe Di Labbio, Lyes Kadem The generation and persistence of a diastolic vortex ring within the healthy left ventricle has gained significant interest over the past two decades. This cardiac vortex has been shown to ease the transport of blood from inflow to outflow, preserving inflowing kinetic energy in a near-optimal manner while also promoting low blood residence time. Nonetheless, despite its practical interest and the multitude of associated diagnostic indices developed over the years, there has been no attempt at modeling the behavior of the cardiac vortex core. In this work, the flow in a healthy left ventricle was simulated in vitro in a double-activation left heart duplicator. The ensuing flow was captured using two-dimensional time-resolved particle image velocimetry in a clinically-relevant plane. Three heart rates were examined (50, 70 and 90 bpm). By comparison to the Lamb-Oseen-Hamel vortex, a one-parameter physics-based empirical fit is developed for the temporal evolution of the vorticity of the cardiac vortex core. The fitting constant is shown to be related to the circulation of the core by the end of the E wave of filling. With a suitable choice of scaling (dependent on the heart rate and ventricle width), the core vorticity at different heart rates appear to collapse onto a single curve. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P23.00004: Computational study of blood flow patterns in a wall-deforming model of the left ventricle under healthy and LVAD-assisted conditions Tingting Yang, Venkat Keshav Chivukula, Alberto Aliseda Left ventricular assist device (LVAD) induce non-physiological flow patterns that are associated with thrombus formation. Numerical modeling of the hemodynamic environment inside simplified geometries of the human left ventricle incorporate wall deformation to simulate healthy and LVAD-assisted conditions. Input boundary conditions and wall deformation are derived from patient-specific measurements. Q-criterion, lambda-2 and streamline visualizations are used to compare the healthy and LVAD cases, better characterizing the impact of LVAD implantation on intraventricular flow patterns. Two vortex rings are formed during mitral filling that break down as they flow towards the ventricular apex, with the remaining filaments washed out through the aortic valve or inflow cannula. Small scale vortices, unreported in previous research with rigid ventricle walls, are found between the apex and the outer cannula wall. A methodology to investigate the physics underlying ventricular filling and emptying with different levels of ventricular contractility (ejection fraction) is demonstrated. LVAD surgical configurations, such as the inflow cannula and outflow graft angles, are studied to provide insights on risk assessment of these surgical techniques. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P23.00005: Simulating Cardiac Fluid-Structure Interaction by an Immersed Finite Element Method Boyce Griffith, Marshall Davey, Charles Puelz, Simone Rossi, Margaret Anne Smith, David Wells Cardiovascular diseases remain the leading causes of death worldwide, and tools for improving diagnosis, treatment planning, or medical device design promise to have a major impact on patient health. Simulating cardiac fluid dynamics across the cardiac cycle motivates the development of models that account for interactions between the blood, the muscular walls of the heart, and the thin cardiac valves. The immersed boundary method is a numerical approach to such problems of fluid-structure interaction (FSI). This talk will describe ongoing work to develop medical image-based models of cardiac FSI for modeling cardiac fluid dynamics. Our model of the heart includes image-based descriptions of the major anatomical features of the heart, including the atria and ventricles, and the nearby great vessels along with idealized anatomical models of the cardiac valves and experimentally constrained biomechanical models. To simulate cardiac FSI, we use an immersed boundary method that employs a finite element description of the immersed structure that enables the use of large-deformation nonlinear elasticity. The talk will outline the numerical approach and model formulation, and will investigate the role of pericardial tethering on establishing realistic intracardiac fluid flows. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P23.00006: Implantation orientation effects of a bileaflet mechanical heart valve in an anatomic left ventricle-aorta configuration Hossein Asadi, Mohammadali Hedayat, Iman Borazjani Three-dimensional high-resolution simulations of a bileaflet mechanical heart valve (BMHV) have been carried out for an anatomic left ventricle-aorta configuration. The geometry of the anatomic left ventricle (LV) is reconstructed from MRI scanned images of a healthy subject and its motion is prescribed based on a lumped parameter model. The highly validated multi-block sharp interface curvilinear immersed boundary method (CURVIB) fluid-structure interaction (FSI) solver is used in which anatomic aorta and LV are discretized with a boundary-conforming and non-conforming curvilinear meshes, respectively. The motion of BMHV is calculated using the strong coupled FSI accelerated with Aitken convergence technique. The simulations are performed for three valve orientations, differing 45 deg from each other for two cardiac cycles. The kinematics of heart valves and instantaneous hemodynamics of each case, as well as, shear stress and platelet activation are analyzed to investigate the performance of each orientation. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P23.00007: An Immersed Interface Method for Biomedical Fluid Structure Interaction Ebrahim Kolahdouz, Brent Craven, Boyce Griffith The mechanical interaction of incompressible viscous flows with immersed bodies is ubiquitously found in medicine and biology. A fluid structure interaction (FSI) coupling strategy is presented within the framework of the immersed interface method that allows fluid and solid subproblems to be solved in a partitioned manner and coupled through interface conditions. The present FSI approach allows for general complex geometries with discrete surfaces while retaining sharp resolution of stresses at the fluid-solid interface. In the coupling of the fluid to the solid, the interfacial fluid stresses drive the solid motion, and a penalty method is used to ensure that the fluid satisfies the no-slip condition along the fluid-solid interface. This approach enables the use of unstructured finite element discretizations of the solid domain while making use of structured-grid solvers for the incompressible Navier-Stokes equations. The algorithm is systematically verified and validated through comparisons with numerical and experimental benchmarks of increasing complexity. Applications of this method to biomedical applications, including the dynamics of bileaflet mechanical heart valves and dynamics of deformable blood clots inside IVC filter will be presented. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P23.00008: Optimal bending rigidity of the aortic valve leaflets Ye Chen, Haoxiang Luo Proper bending stiffness and the ability to quickly respond to the dynamic pressure load on their surfaces are critical for the heart valves to carry out their physiological functions. Studies on how the flexibility of the leaflets affects the fluid-structure interaction (FSI) of heart valves are still very limited. In this talk, three-dimensional FSI simulations of a bioprosthetic aortic valve are performed using a parallelized immersed-boundary method. The pressure distribution over the leaflets and transient force on the valve are calculated The thickness of the leaflets is varied from 0.1 mm to 0.8 mm, which results a wide range of non-dimensional bending rigidity EB*, normalized by the transvalvular pressure gradient. For valves with low bending rigidity (EB* around 1.0E-2), the valve functions normally and produces physiological characteristics of healthy valves. However, exceedingly low rigidity (for example, EB* $=$ 1.2E-3) leads to flapping motion of the leaflets and impairs the valve's performance. Stiffer valves (EB* greater than 0.2) are more difficult to open and slower to close, which leads to higher resistance and a reduced flow rate during systole. The results reveal the existence of an optimal range of bending rigidity for the valve, where EB* is roughly between 0.003 and 0.04. Effects of bending rigidity on valve deformation and flow characteristics will also be discussed. [Preview Abstract] |
Monday, November 25, 2019 7:00PM - 7:13PM |
P23.00009: Aortic Wall Shear Analysis from Asymmetric Prosthetic Heart Valve Design Alexandros Rosakis, Morteza Gharib Asymmetrically stiffened aortic trileaflet valve leaflets can divert the systolic flow away from the stiffened leaflets and into the wall of the aortic root. Asymmetrical stiffening of the aortic valve can be caused by aortic valve stenosis. We show the different flow profiles caused by different combinations of stiffened and unstiffened leaflets. Furthermore, we describe how this asymmetric stiffening alters the wall shear stress on a model aorta. This investigation can be used to better understand disease states in patients with aortic valve stenosis. Moreover, understanding the effects of asymmetric leaflet stiffening on the aortic flow may allow us to design patient specific prosthetic polymer heart valves. These valves would have carefully tuned leaflet thicknesses that would direct the systolic flow in a way that minimizes damage to the patient's aortic wall and better resembles natural healthy heart valves. [Preview Abstract] |
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