Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session BL: Bio-Fluids: Cardiac Flows |
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Chair: Juan C. del Alamo, University of California, San Diego Room: 103A |
Sunday, November 23, 2008 10:30AM - 10:43AM |
BL.00001: Flow within Physical Models of the Vertebrate Embryonic Heart Nhi Nguyen, Arvind Santhanakrishnan, Laura Miller Vertebrate cardiogenesis is believed to be partially regulated by fluid forces imposed by blood flow in addition to myocardial activity and other epigenetic factors. Recent \textit{in vitro} studies in embryonic cardiogenesis (see Hove et al., Nature, 2003) show that blood flowing through the embryonic heart tube creates shear forces necessary for the formation and development of the heart valves. It is suggested that these flow driven forces provide a biomechanical stimulus to the endothelial surface layer, which then feed into the biochemical regulatory networks that initiate heart looping and chamber ballooning. To understand the flow field within the embryonic heart, flow visualization experiments were performed on a series of physical models that represent the different morphological stages of early heart development. The chamber and valve depths of the models as well as the Reynolds numbers were varied in this study. Different compositions of solutions consisting of corn syrup and water were used as the fluid media to examine Reynolds numbers from 0.01 to 1000, corresponding to a scale of the early heart tube to the adult heart. The observed results showed that vortex formation within the chambers occurred for Reynolds numbers in the range of 1-10. This transition to vortical flow appears to be highly sensitive to the chamber and valve depths within the model. [Preview Abstract] |
Sunday, November 23, 2008 10:43AM - 10:56AM |
BL.00002: Fluid-structure interaction and electrophysiology of the embryonic heart Laura Miller, Arvind Santhanakrishnan, Anil Shenoy The morphology, muscle mechanics, fluid dynamics, conduction properties, and molecular biology of the developing embryonic heart have received much attention in recent years because of the importance of both fluid and elastic forces in shaping the heart as well as the striking relationship between the heart's evolution and development. Very few studies, however, have investigated the coupling between each of these components. In this presentation, the fully coupled fluid-structure interaction problem of the embryonic heartbeat will be investigated over a range morphological phenotypes and Reynolds numbers. The immersed boundary method was used to numerically solve the Navier-Stokes equations with immersed elastic boundaries. Flow visualization was carried out in corresponding physical models using particle image velocimetry, dye injection and pH indicator methods. For select problems, the Fitzhugh-Nagumo equations were solved separately to generate action potentials along the heart's surface, which were then used to drive contractions in the immersed boundary simulations. [Preview Abstract] |
Sunday, November 23, 2008 10:56AM - 11:09AM |
BL.00003: Estimation of two-dimensional intraventricular velocity and pressure maps by digital processing conventional color-Doppler sequences Damien Garcia, Juan C. del Alamo, David Tanne, Cristina Cortina, Raquel Yotti, Francisco Fernandez-Aviles, Javier Bermejo Clinical echocardiographic quantification of blood flow in the left ventricle is limited because Doppler methods only provide one velocity component. We developed a new technique to obtain two-dimensional flow maps from conventional transthoracic echocardiographic acquisitions. Velocity and pressure maps were calculated from color-Doppler velocity (apical long-axis view) by solving the continuity and Euler equations under the assumptions of zero transverse fluxes of mass and momentum. This technique is fast, clinically-compliant and does not require any specific training. Particle image velocimetry experiments performed in an atrioventricular duplicator showed that the circulation and size of the diastolic vortex was quantified accurately. Micromanometer measurements in pigs showed that apex-base pressure differences extracted from two-dimensional maps qualitatively agreed with micromanometer data. Initial clinical measurements in healthy volunteers showed a large prograde vortex. Additional retrograde vortices appeared in patients with dilated cardiomyopathy and left ventricular hypertrophy. [Preview Abstract] |
Sunday, November 23, 2008 11:09AM - 11:22AM |
BL.00004: Correlation of Left Ventricle Hydrodynamic Parameters with Diastolic Dysfunction Kelley Stewart, Rahul Kumar, John Charonko, Pavlos Vlachos, William Little Cardiac flows are by nature intricate, involving unsteadiness, and transition to turbulence. In the presence of disease, their complexity is increased and the pumping efficiency of the left heart is compromised. Color M-mode echocardiography, used herein, can provide valuable clinical data, however their physical interpretation is often lacking. The present work is based on the notion that the normal diastolic filling pattern in the left ventricle (LV) is disrupted by diastolic dysfunction (DD). As such, a LV filling efficiency parameter incorporating intraventricular pressure differences and a novel break-point vortex ring propagation velocity, calculated by a statistical change point algorithm has been developed to characterize the effectiveness of diastole and its subsequent decline because of DD. An automated algorithm analyzed clinical data from 125 patients spanning the 4 stages of DD. The results provide insight on the significance of the various parameters on the progression of DD and provide and novel approach for understanding clinical echo data. [Preview Abstract] |
Sunday, November 23, 2008 11:22AM - 11:35AM |
BL.00005: Numerical Simulations of Blood Flows in the Left Atrium Lucy Zhang A novel numerical technique of solving complex fluid-structure interactions for biomedical applications is introduced. The method is validated through rigorous convergence and accuracy tests. In this study, the technique is specifically used to study blood flows in the left atrium, one of the four chambers in the heart. Stable solutions are obtained at physiologic Reynolds numbers by applying pulmonary venous inflow, mitral valve outflow and appropriate constitutive equations to closely mimic the behaviors of biomaterials. Atrial contraction is also implemented as a time-dependent boundary condition to realistically describe the atrial wall muscle movements, thus producing accurate interactions with the surrounding blood. From our study, the transmitral velocity, filling/emptying velocity ratio, durations and strengths of vortices are captured numerically for sinus rhythms (healthy heart beat) and they compare quite well with reported clinical studies. The solution technique can be further used to study heart diseases such as the atrial fibrillation, thrombus formation in the chamber and their corresponding effects in blood flows. [Preview Abstract] |
Sunday, November 23, 2008 11:35AM - 11:48AM |
BL.00006: Modeling Flow Past a TrapEase Inferior Vena Cava Filter Michael Singer, William Henshaw, Stephen Wang This study uses three-dimensional computational fluid dynamics to evaluate the efficacy of the TrapEase inferior vena cava (IVC) filter. Hemodynamics of the unoccluded and partially occluded filter are examined, and the clinical implications are assessed. The IVC, which is the primary vein that drains the legs, is modeled as a straight pipe, and a geometrically accurate model of the filter is constructed using computer aided design. Blood is modeled as a homogeneous, incompressible, Newtonian fluid, and the method of overset grids is used to solve the Navier-Stokes equations. Results are corroborated with in-vitro studies. Flow around the unoccluded filter demonstrates minimal disruption, but spherical clots in the downstream trapping position lead to regions of stagnant and recirculating flow that may promote further clotting. The volume of stagnant flow and the peak wall shear stress increase with clot volume. For clots trapped in the upstream trapping position, flow is disrupted along the cava wall downstream of the clot and within the filter. The shape and location of trapped clots also effect the peak wall shear stress and may impact the efficacy of the filter. [Preview Abstract] |
Sunday, November 23, 2008 11:48AM - 12:01PM |
BL.00007: Optimization of an idealized Y-Shaped Extracardiac Fontan Baffle Weiguang Yang, Jeffrey Feinstein, V. Mohan Reddy, Alison Marsden Research has showed that vascular geometries can significantly impact hemodynamic performance, particularly in pediatric cardiology, where anatomy varies from one patient to another. In this study we optimize a newly proposed design for the Fontan procedure, a surgery used to treat single ventricle heart patients. The current Fontan procedure connects the inferior vena cava (IVC) to the pulmonary arteries (PA's) via a straight Gore-Tex tube, forming a T-shaped junction. In the Y-graft design, the IVC is connected to the left and right PAs by two branches. Initial studies on the Y-graft design showed an increase in efficiency and improvement in flow distribution compared to traditional designs in a single patient-specific model. We now optimize an idealized Y-graft model to refine the design prior to patient testing. A derivate-free optimization algorithm using Kriging surrogate functions and mesh adaptive direct search is coupled to a 3-D finite element Navier-Stokes solver. We will present optimization results for rest and exercise conditions and examine the influence of energy efficiency, wall shear stress, pulsatile flow, and flow distribution on the optimal design. [Preview Abstract] |
Sunday, November 23, 2008 12:01PM - 12:14PM |
BL.00008: Vortex Formation Time in Progression of Cardiac Dysfunction Arash Kheradvar, Morteza Gharib We previously showed that the trans-mitral vortex formation is affected by functionality of the cardiac left ventricle (LV). Additionally, we showed that in a healthy heart, the vortex formation time (VFT) closely follows the suggested values obtained \textit{in vitro} by Gharib et al. Here, we assess the changes in VFT during the progress of cardiac dysfunction. In LV, the VFT can be independently derived from volumetric parameters and the ventricular ejection fraction (EF): \[ VFT=\frac{4(1-\beta )}{\pi }.\alpha ^3.EF \] where $\beta $ is the contribution of atrial contraction phase to the LV stroke volume, and $\alpha $ is the ratio of the cubic root of LV end-diastolic volume to the effective mitral valve area diameter. Thus, $\alpha ^{3}$ is considered a non-dimensional measure for LV geometry. Substituting the values of $\alpha $, $\beta $ and EF obtained from patients in different stages of diastolic dysfunction into VFT equation would result in distinct range of VFT for each stage. This equation is also attributable to systolic dysfunction where EF has a significant contribution. Accordingly, by comparing the value of VFT during the progression of cardiac dysfunction, VFT can be considered as a factor that determines the deterioration of LV function, either from systolic and/or diastolic origin. [Preview Abstract] |
Sunday, November 23, 2008 12:14PM - 12:27PM |
BL.00009: Numerical study of the influence of the hinge gap width on the hinge flow fields of bileaflet mechanical heart valves Helene Simon, Liang Ge, Fotis Sotiropoulos, Ajit Yoganathan Previous clinical and in-vitro studies have shown that the complex non-physiologic hemodynamics occurring in the hinge region of bileaflet mechanical heart valves promotes blood cell damage and thrombus formation. Modifying the hinge design could improve the flow and thus reduce the associated blood cell trauma. This study aims at investigating numerically the effect of the hinge gap width on the flow field. The governing equations are solved using a Cartesian sharp interface immersed boundary method coupled with a hybrid staggered/non staggered control volume approach. The hinge dimensions are obtained from MicroComputed Tomography of a clinical valve. The leaflet motion and inlet velocity profile are imposed based on the Fluid-Structure Interaction simulations of the bulk flow of a valve placed under aortic physiologic conditions. 3D pulsatile flows through two hinge designs are presented along with their Lagrangian analysis. The hinge gap width is shown to have a strong influence on the flow, and thus on blood cell trauma. [Preview Abstract] |
Sunday, November 23, 2008 12:27PM - 12:40PM |
BL.00010: A study of the flow-leaflet interaction R. Ledesma, R. Zenit, G. Pulos The manufacture of prosthetic heart valves is a relatively simple process. Valves made with biomaterials simply copy the ``design'' of the original ones, because of the limited understanding of the physical mechanism involved in the proper performance of valves. The identification of the parameters that determine the valve performance will help to improve the prosthetic designs and to minimize the health complications. In this work we study the flow-leaflet interaction in a pulsating flow, with the purpose of evaluating the influence of the material properties and leaflet dimensions. A 2D flow channel was design to obtain measurements of the leaflet deflection, for different flow conditions. Using a PIV system, measurements of the flow velocity fields are also obtained. Preliminary results show that the deflection of the leaflet and the proper open-close cycle, that determines the valve performance, is directly related to the leaflet length, thickness and material properties. We have identified the range of parameters for which the valve performance is acceptable. [Preview Abstract] |
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