Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session A16: Biofluids: Physiological I - Computational Studies in Cardiovascular Flows |
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Chair: Martina Bukac, University of Pittsburgh Room: 304 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A16.00001: Effect of Trabeculations on the Hemodynamics of Left Ventricle: A Computational Study Vijay Vedula, Jung-Hee Seo, Richard George, Albert Lardo, Rajat Mittal The endocardium of the human left ventricle is not smooth. There are surface trabeculations as well as papillary muscles that protrude deep into the ventricular cavity. However, most models of ventricular hemodynamics ignore the presence of these surface structures and assume a smooth endocardial surface. Several key questions arise regarding the impact of these structures on ventricular hemodynamics. These surface ``roughness elements'' could enhance mixing and dissipation. Moreover, the interstitial regions within the trabeculae might be prone to flow stasis, and this has implications for ventricular thrombogenesis. In the present study, we use flow simulation to study this issue for CT derived models of normal human left ventricle. We focus on the near-wall dynamics of the flow and employ a number of different diagnostics to examine the flow dynamics and ``washout'' in this region. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A16.00002: Fluid Dynamics of Contrast Dispersion in Coronary Arteries: Mechanism and Implications for Identification of Flow-Limiting Lesions Parastou Eslami, Jung-Hee Seo, Albert C. Lardo, Rajat Mittal Recent coronary computed tomography angiography studies have noted the presence of axial contrast concentration gradients in stenosed coronary arteries, but the mechanism responsible for this phenomenon is not well understood. We use computational fluid dynamics to study intracoronary contrast dispersion and the correlation of concentration gradients with intracoronary blood flow and stenotic severity. Simulations of flow and contrast dispersion in both canonical and patient derived models of the left coronary artery (LCA) are carried out with a prescribed contrast bolus profile, and stenoses of varying severities (0{\%} to 80{\%}) considered. Data from our CFD simulations show the presence of measurable contrast gradients, the magnitude of which is found to decrease monotonically with stenotic severity and increase monotonically with the pressure drop across the stenosis. All simulated cases indicate a strong inverse correlation between contrast gradients and coronary flow rate. The study reveals that contrast gradients are generated by intracoronary advection effects, and therefore, encode coronary flow velocity. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A16.00003: Hemodynamics and flow-vessel interaction in patient-specific aorta using unified lattice Boltzmann computation and simulation Huidan (Whitney) Yu, Zhiqiang Wang, Ye Zhao, Shawn D. Teague Patient-specific blood flow simulation is mainly relying on the utilization of commercial software. Geometrical simplification and approximation are usually made thus weaken the capability to aid clinical diagnose and assessment. We develop a unified computing platform to simulate patient-specific hemodynamics and flow-vessel interaction using lattice Boltzmann method (LBM), which tightly integrates anatomical-structure extraction from imaging data and numerical simulation in one computation mesh structure, where the LBM solves level set equation for image segmentation and Navier-Stokes equation for fluid dynamics respectively. The patient-specific vessel geometry, volumetric ratio of solid versus fluid, and the orientation of the boundary obtained with high accuracy seamlessly feed to the numerical simulation needs. In order to better treat the complex geometry, we specifically develop volumetric lattice Boltzmann scheme which strictly satisfies mass conservation when boundary moves. Validation study is on hemodynamics and flow-vessel interaction in healthy and diseased aortas. Flow rate and structure, pressure and vorticity distribution, as well as wall normal and shear stresses, are revealed in both cases. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A16.00004: Coupled Hemodynamic-Biochemical Modeling of Thrombus Formation in Infarcted Left Ventricles Jung Hee Seo, Vijay Vedula, Richard George, Rajat Mittal Patients with heart failure (HF) and left ventricular (LV) systolic dysfunction have higher rates of thromboembolic events including embolic stroke and peripheral arterial thrombi. A common cause of arterial emboli in HF patients is myocardial infarction (MI) and subsequent left ventricular thrombus (LVT) formation. Stagnation of blood and endocardial injury are hypothesized to promote the development of LVT. The identification of high risk patients and the pharmacologic prevention of LVT formation are the keys to preventing embolic events. Stratification of patients at risk for LVT formation is currently limited, and primarily based on global assessment of ventricular function and image based assessment of ventricular wall motion. In this study, we explore a method to predict LVT risk using a multi-physics computational model. The blood flow in the left ventricle is simulated by solving the incompressible Navier-Stokes equation using an immersed boundary method and this is coupled to a convection-diffusion-reaction equation based model of platelet activation and coagulation. The results are then correlated with the other hemodynamic metrics such as wall shear stress and residence time to develop quantitative metrics for the LVT risk prediction. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A16.00005: Patient-specific simulation of a trileaflet aortic heart valve in a realistic left ventricle and aorta Anvar Gilmanov, Trung Le, Henryk Stolarski, Fotis Sotiropoulos We develop a patient-specific model of the left ventricle consisting of: (1) magnetic-resonance images (MRI) data for wall geometry and kinematics reconstruction of the left ventricle during one cardiac cycle and (2) an elastic trileaflet aortic heart valve implanted in (3) a realistic aorta interacting with blood flow driven by the pulsating left ventricle. Blood flow is simulated via a new fluid-structure interaction (FSI) method, which couples the sharp-interface CURVIB [L. Ge, F. Sotiropoulos, JCP, (2007)] for handling complex moving boundaries with a new, rotation-free finite-element (FE) formulation for simulating large tissue deformations [H. Stolarski, A. Gilmanov, F. Sotiropoulos, IJNME, (2013)] The new FE shell formulation has been extensively tested and validated for a range of relevant problems showing good agreements. Validation of the coupled FSI-FE-CURVIB model is carried out for a thin plate undergoing flow-induced vibrations in the wake of a square cylinder and the computed results are in good agreement with published data. The new approach has been applied to simulate dynamic interaction of a trileaflet aortic heart valve with pulsating blood flow at physiological conditions and realistic artery and left ventricle geometry. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A16.00006: Computational study of the effect of dynamic wall confinement on ventricular filling Xudong Zheng, Qian Xue Ventricular filling is a major cardiac phase in which the freshly oxygenated blood in the left atrium (LA) enters the left ventricle (LV). There is an increasing consensus that dynamics of transmitral blood flow during filling plays a critical role in dictating overall cardiac health and predicting early changes in cardiac function. The ventricular flow during filling is determined by the interplay of incoming mitral jet and myocardial wall confinement and manifested by a complex morphing pattern of an asymmetric vortex ring. In the current study, we employ computational simulations to explore the effects of dynamic wall confinement on ventricular flow in an idealized left ventricle model. The effects of radial and longitudinal confinement as well as wall motion will be investigated, with special interests on vortex dynamics, such as vortex ring tilting, pinch off and breakdown, intraventricular pressure drop, filling velocity, energy dissipation and blood mixing. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A16.00007: Pulsatile flow through idealized trabeculae Nicholas Battista, Laura Miller Trabeculae begin to form in the human developing heart for Reynolds numbers on the order of 10. Other hearts, such as the squid heart, have trabeculae for Re on the order of 10 and larger. The effect of trabeculae on the flow in this range of Re is not well understood. In this study, computational fluid dynamics is used to quantify the effects of Reynolds number and idealized trabeculae height on the resulting flows. An adaptive and parallelized version of the immersed boundary method (IBAMR) is used to solve the fluid-structure interaction problem. We see the formation of vortices depends upon Re and trabeculae height. We then explore how the periodicity of the flow effects vortex formation and shear patterns. This is important because it is thought that these dynamic processes are important to the generation of shear at the endothelial surface layer and strains at the epithelial layer, which will aid in proper development and functionality. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A16.00008: Influence of the heart rate and atrioventricular delays on vortex evolution and blood transport inside the left ventricle Sahar Hendabadi, Pablo Martinez-Legazpi, Yolanda Benito, Javier Bermejo, Juan Carlos del Alamo, Shawn Shadden Cardiac resynchronization therapy (CRT) is used to help restore coordinated pumping of the ventricles by overcoming delays in electrical conduction due to cardiac disease. This is accomplished by a specialized cardiac pacemaker that is able to adjust the atrioventricular (AV) delay.A major clinical challenge is to adjust the pacing strategy to best coordinate the blood flow mechanics of ventricular filling and ejection. To this end, we have studied the difference in the vortex formation and its evolution inside the left ventricle (LV) for 4 different AV delays in a cohort of patients with implanted pacemakers. A reconstruction algorithm was used to obtain 2D velocity over the apical long-axis view of the LV from color Doppler and B-mode ultrasound data. To study blood transport, we have identified Lagrangian coherent structures to determine moving boundaries of the blood volumes injected to the LV in diastole and ejected to the aorta in systole. In all cases, we have analyzed the differences in filling and ejection patterns and the blood transport during the E-wave and A-wave formation.Finally we have assessed the influence of the AV delay on 2 indices of stasis, direct flow and residence time.The findings shed insight to the optimization of AV delays in patients undergoing CRT. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A16.00009: Hemodynamic consequences of LPA stenosis in single ventricle stage 2 LPN circulation with automatic registration Daniele E. Schiavazzi, Ethan O. Kung, Adam L. Dorfman, Tain-Yen Hsia, Alessia Baretta, Gregory Arbia, Alison L. Marsden Congenital heart diseases such as hypoplastic left heart syndrome annually affect about 3{\%} of births in the US alone. Surgical palliation of single ventricle patients is performed in stages. Consequently to the stage 2 surgical procedure or other previous conditions, a stenosis of the left pulmonary artery (LPA) is often observed, raising the clinical question of whether or not it should be treated. The severity of stenoses are commonly assessed through geometric inspection or catheter in-vivo pressure measurements with limited quantitative information about patient-specific physiology. The present study uses a multiscale CFD approach to provide an assessment of the severity of LPA stenoses. A lumped parameter 0D model is used to simulate stage 2 circulation, and parameters are automatically identified accounting for uncertainty in the clinical data available for a cohort of patients. The importance of the latter parameters, whether alone or in groups, is also ranked using forward uncertainty propagation methods. Various stenosis levels are applied to the three-dimensional SVC-PA junction model using a dual mesh-morphing approach. Traditional assessments methodologies are compared to the results of our findings and critically discussed. [Preview Abstract] |
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