Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H16: Biofluids: Heart Ventricles and Assist Devices |
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Chair: Rajat Mittal, Johns Hopkins University Room: 28B |
Monday, November 19, 2012 10:30AM - 10:43AM |
H16.00001: Simulating Pediatric Ventricular Assist Device Operation Using Fluid Structure Interaction Chris Long, Yuri Bazilevs, Alison Marsden Ventricular Assist Devices (VADs) provide mechanical circulatory support to patients in heart failure. They are primarily used to extend life until cardiac transplant, but also show promise as a ``bridge-to-recovery'' device in pediatric patients. Commercially available pediatric pumps are pulsatile displacement pumps, with two distinct chambers for air and blood separated by a thin, flexible membrane. The air chamber pneumatically drives the membrane, which drives blood through the other chamber via displacement. The primary risk factor associated with these devices is stroke or embolism due to thrombogenesis in the blood chamber, occurring in as many as 40\% of patients. Our goal is to perform simulations that accurately model the hemodynamics of the device, as well as the non-linear membrane buckling. We apply a finite-element based fluid solver, with an Arbitrary Lagrangian-Eulerian (ALE) framework to account for mesh motion. Isogeometric Analysis with a Kirchhoff-Love shell formulation is used on the membrane, and two distinct fluid subdomains are used for the air and blood chambers. The Fluid Structure Interaction (FSI) problem is solved simultaneously, using a Matrix Free method to model the interactions at the fluid-structure boundary. Methods and results are presented. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H16.00002: Heart Rate and AV delay modify left ventricular filling vortex properties Juan C. del Alamo, Yolanda Benito, Javier Bermejo, Marta Alhama, Raquel Yotti, Candelas Perez del Villar, Pablo Martinez-Legazpi, Ana Gonzalez Mansilla, Francisco Fernandez-Aviles Intraventricular flow generates a vortex ring during rapid filling that optimizes filling, couples inflow kinetic energy to ejection, improves blood mixing and avoids stasis. LV vorticity has been related to chamber geometrical properties, but the effects of electrical events have never been characterized, partly due to the difficulty of performing MRI in patients with implanted devices. We have recently developed a new method that allows measuring vortex properties by processing conventional transthoracic color-Doppler sequences. Using this modality, 27 patients carrying an implantable cardiac resynchronization device were studied after AV optimization at 100 beats per minute. Our results reveal that, compared to optimal AV, the main vortex component remained closer to the base during 100BPM (difference = -20{\%} of Lax length, p$<$ .05) and closer to the apex when AV is minimized (diff= +11{\%} of Lax, p$<$ .05). Radius, circulation and energy of the vortices were larger when AV is maximized (p$<$ .05). In conclusion, the duration of diastole, as modulated by heart rate and AV-delay, significantly modifies intraventricular vortex dynamics. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H16.00003: On the clinical characterization of impulse and suction force contributions by the diastolic left ventricular vortex Pablo Martinez-Legazpi, Marta Alhama, Yolanda Benito, Javier Bermejo, Raquel Yotti, Esther Perez-David, Alicia Barrio, Candelas Perez-del-Villar, Ana Gonzalez-Mansilla, Francisco Fernandez-Aviles, Juan C. del Alamo One of the fluid-dynamic mechanisms that characterize the diastolic phase of the cardiac cycle is the formation of a left ventricular (LV) vortex ring that has been proposed to improve LV filling. However, direct clinical quantification of the contribution of this vortex to LV filling is elusive. In this clinical study, we considered 20 patients with dilated cardiomyopathy (DCM) and 40 healthy volunteers. We have developed and validated a method that derives two-dimensional maps of the LV flow from standard color-Doppler sequences. This study employs the new imaging modality in combination with a vortex identification method and a panel method in order to isolate and estimate the direct contribution of the LV vortex to fluid impulse and suction force during filling in the healthy and diseased populations. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H16.00004: High-resolution numerical simulation of Left Ventricular Hemodynamics Guided by in-vivo Cardiac Magnetic Resonance Data Trung Le, Fotis Sotiropoulos, Lucia Mirabella, Brandon Chaffins, Arvind Santhanakrishnan, John Oshinski, Ajit Yoganathan We study the fluid dynamics within a patient-specific left ventricle (LV) during diastole using both numerical simulations and in-vivo data. The kinematics of the LV is reconstructed from high-resolution Magnetic Resonance Imaging (MRI) data acquired on a healthy volunteer, using image segmentation and a surface registration process. The flow velocity is acquired using phase-contrast MRI at the mitral orifice and at an additional parallel plane inside the ventricle. Numerical simulations are carried out using the CURVIB method (Ge et al., JCP, 2007) with the MRI reconstructed LV wall motion imposed as boundary condition. The numerical simulations show the highly dynamic environment of the flow field. The mitral vortex ring is formed during early diastolic filling and breaks down into small scale structures. The simulated hemodynamics are compared with phase-contrast MRI measurements and previous simulations in which the LV wall motion was obtained from a lumped parameter model (Le and Sotiropoulos, Eur. J. Mechanics B - Fluids, 2012) [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H16.00005: Right Ventricular Hemodynamics in Patients with Pulmonary Hypertension James Browning, Brett Fenster, Jean Hertzberg, Joyce Schroeder Recent advances in cardiac magnetic resonance imaging (CMR) have allowed for characterization of blood flow in the right ventricle (RV), including calculation of vorticity and circulation, and qualitative visual assessment of coherent flow patterns. In this study, we investigate qualitative and quantitative differences in right ventricular hemodynamics between subjects with pulmonary hypertension (PH) and normal controls. Fifteen (15) PH subjects and 10 age-matched controls underwent same day 3D time resolved CMR and echocardiography. Echocardiography was used to determine right ventricular diastolic function as well as pulmonary artery systolic pressure (PASP). Velocity vectors, vorticity vectors, and streamlines in the RV were visualized in Paraview and total RV Early (E) and Atrial (A) wave diastolic vorticity was quantified. Visualizations of blood flow in the RV are presented for PH and normal subjects. The hypothesis that PH subjects exhibit different RV vorticity levels than normals during diastole is tested and the relationship between RV vorticity and PASP is explored. The mechanics of RV vortex formation are discussed within the context of pulmonary arterial pressure and right ventricular diastolic function coincident with PH. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H16.00006: Computational Modeling of the Effects of Myocardial Infarction on Left Ventricular Hemodynamics Vijay Vedula, Jung Hee Seo, Rajat Mittal, Stefania Fortini, Giorgio Querzoli Most in-vivo and modeling studies on myocardial infarction and ischemia have been directed towards understanding the left ventricular wall mechanics including stress-strain behavior, end systolic pressure-volume correlations, ejection fraction and stroke work. Fewer studies have focused on the alterations in the intraventricular blood flow behavior due to local infarctions. Changes in the motion of the endocardium can cause local circulation and stagnation regions; these increase the blood cell residence time in the left ventricle and may eventually be implicated in thrombus formation. In the present study, we investigate the effects of myocardial infarction on the ventricular hemodynamics in simple models of the left ventricle using an immersed-boundary flow solver. Apart from the Eulerian flow features such as vorticity and velocity flow fields, pressure distribution, shear stress, viscous dissipation and pump work, we also examine the Lagrangian dynamics of the flow to gain insights into the effect of flow dynamics on thrombus formation. The study is preceded by a comprehensive validation study which is based on an in-vitro experimental model of the left ventricle and this study is also described. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H16.00007: A Methodology for Quantifying Heart Function in the Embryonic Zebrafish Brennan Johnson, Deborah Garrity, Lakshmi Dasi Several studies have linked epigenetic factors such as blood flow dynamics and cardiac function to proper heart development. To better understand this process, it is essential to develop robust quantitative methods to investigate the blood dynamics and wall kinematics in vivo. Here, we develop a methodology that can be used throughout the early stages of development which requires no specialized equipment other than a bright field microscope and high-speed camera. We use the embryonic zebrafish as our model due to its superb optical access and widespread acceptance as a powerful model for human heart development. Using these methods, we quantify blood flow rates, stroke volume, cardiac output, ejection fraction, and other important parameters related to heart function. We also investigate the pumping mechanics from heart tube to looped configuration. We show that although the mechanism changes fundamentally, it does so in a continuous fashion that can incorporate combined pumping mechanisms at intermediate stages. This work provides a basis for quantitatively comparing normal and abnormal heart development, and may help us gain a better understanding of congenital heart defects. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H16.00008: Human Aorta Is a Passive Pump Niema Pahlevan, Morteza Gharib Impedance pump is a simple valveless pumping mechanism that operates based on the principles of wave propagation and reflection. It has been shown in a zebrafish that a similar mechanism is responsible for the pumping action in the embryonic heart during early stages before valve formation. Recent studies suggest that the cardiovascular system is designed to take advantage of wave propagation and reflection phenomena in the arterial network. Our aim in this study was to examine if the human aorta is a passive pump working like an impedance pump. A hydraulic model with different compliant models of artificial aorta was used for series of in-vitro experiments. The hydraulic model includes a piston pump that generates the waves. Our result indicates that wave propagation and reflection can create pumping mechanism in a compliant aorta. Similar to an impedance pump, the net flow and the flow direction depends on the frequency of the waves, compliance of the aorta, and the piston stroke. [Preview Abstract] |
Monday, November 19, 2012 12:14PM - 12:27PM |
H16.00009: Characterization of human left ventricle flow patterns using ultrasound and Lagrangian coherent structures Sahar Hendabadi, Juan Carlos del Alamo, Yolanda Benito, Raquel Yotti, Javier Bermejo, Shawn Shadden We discuss work towards understanding human left ventricle (LV) transport and mixing characteristics in normal subjects and patients with dilated cardiomyopathy. Prior studies have shown that the fluid dynamics in the left ventricle (LV) play a major role in dictating overall cardiac health. This study utilizes a noninvasive method to obtain planar velocity data over the apical long-axis view of the LV from color Doppler and B-mode ultrasound measurements. We use a Lagrangian measure to study unsteady behavior of blood transport inside the LV. We compute finite-time Lyapunov exponent (FTLE) fields to extract Lagrangian coherent structures (LCS) from the empirical data. This application presents a particular challenge to Lagrangian computations due to the presence of moving flux, and no-flux, boundaries. We describe a method for unstructured grid generation from the LV motion, and LCS computation on the deforming unstructured grid. Results demonstrate that LCS reveal the moving boundaries confining the blood volume injected to the LV in diastole and ejected into the aorta in systole. We discuss findings related to the quantification of the LV vortex, whose geometry and motion is thought to be an important indicator of cardiac health. [Preview Abstract] |
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