Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session GE: Biofluids V: Cardiac Flows |
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Chair: Stavros Tavoularis, University of Ottawa Room: 101E |
Monday, November 23, 2009 8:00AM - 8:13AM |
GE.00001: Unsteady flows modeling using Smoothed Particle Hydrodynamics Shahrokh Shahriari, Ibrahim Hassan, Lyes Kadem Cardiovascular diseases are the major cause of death in North America. Investigation of blood flow behavior in the cardiovascular system is, therefore, of great interest in biomedical engineering and cardiology. These kinds of flows are characterized by highly inertial pulsatile effects and deformable boundaries. The most important limitation of conventional numerical methods for simulating such flows is their main nature dependence on the process of mesh generation; distortion and remeshing that are numerically expensive. An alternative to overcome these limitations can be the new generation of numerical methods called meshfree methods. Smoothed Particle Hydrodynamics (SPH) is a Lagrangian meshfree method created originally to simulate astrophysical phenomena and later developed for applications in continuum solid and fluid mechanics. In this investigation, the potential of SPH method to model pulsating laminar flow in simplified (rigid) geometries found in the cardiovascular system such as left heart cavity and stenosed artery are examined. This work represents the first attempt to model internal pulsatile flows for a variety of Reynolds numbers using SPH. Although reaching physiological conditions still needs several improvements, SPH showed a good capability and could become a promising numerical method to simulate cardiovascular flows. [Preview Abstract] |
Monday, November 23, 2009 8:13AM - 8:26AM |
GE.00002: Left ventricle of mammalian hearts optimzed for high hydrodynamic efficiency Liang Ge, Ali Azadani, Elaine Tseng Mammalian hearts have four chambers: two atria (left and right) and two ventricles (left and right). The left ventricle (LV) is the primary pumping engine that pumps blood to all end organs of the body. The energetic efficiency of LV is therefore crucial for life. An important factor that contributes to the overall LV pumping efficiency is the hydrodynamic cost of blood flow within the LV chamber. LV blood flow is created by the cyclical expansion/contraction motion of LV wall and its hydrodynamic cost is certainly affected by the geometry and motion of LV wall. In this work we investigated the relationship between the hydrodynamic cost of LV filling/ejecting and LV geometry/motion and showed that the geometry and motion of mammalian hearts were optimized to minimize the hydrodynamic cost of LV blood flow. [Preview Abstract] |
Monday, November 23, 2009 8:26AM - 8:39AM |
GE.00003: Early embryonic intra-cardiac flow fields at three idealized ventricular morphologies Kerem Pekkan, Mohammad Jamaly, Burak Kara, Bradley Keller, Fotis Sotiropoulos Pulsatile 3D multiple inlet/outlet flow within tiny (100-300$\mu $m dia) embryonic ventricles feature distinct intra-cardiac flow streams whose role in regulating the morphogenesis of spiral aorto-pulmonary septum has long been debated. The low Re number flow regimes limit mixing of these streams as replicated in our flow-visualization experiments with chick embryos. A state-of-the art high-resolution immersed boundary CFD solver which was developed for complex patient-specific cardiovascular internal flow problems is applied and optimized for this problem. Idealized tubular ventricles at 3 major embryonic stages (straight, C- and D- loops) are created by our sketch-based anatomical editing tool. CFD results are validated with PIV measurements acquired from a micro-fabricated C-loop stage replica and in vivo flow vis data from confocal microscopy. This model provided the inlet velocity profile for arterial models and flow fields at the inner curvature of embryonic hearts for different ventricular topologies are compared for off-design modes. [Preview Abstract] |
Monday, November 23, 2009 8:39AM - 8:52AM |
GE.00004: Simulations of heart mechanics over the cardiac cycle Stavros Tavoularis, Matthew Doyle, Yves Bourgault This study is concerned with the numerical simulation of blood flow and myocardium motion with fluid-structure interaction of the left ventricle (LV) of a canine heart over the entire cardiac cycle. The LV geometry is modeled as a series of nested prolate ellipsoids and is capped with cylindrical tubes representing the inflow and outflow tracts. The myocardium is modeled as a multi-layered, slightly compressible, transversely isotropic, hyperelastic material, with each layer having different principal directions to approximate the fibrous structure. Blood is modeled as a slightly compressible Newtonian fluid. Blood flow into and out of the LV is driven by left atrial and aortic pressures applied at the distal ends of the inflow and outflow tracts, respectively, along with changes in the stresses in the myocardium caused by time-dependent changes in its material properties, which simulate the cyclic contraction and relaxation of the muscle fibers. Numerical solutions are obtained with the use of a finite element code. The computed temporal and spatial variations of pressure and velocity in the blood and stresses and strains in the myocardium will be discussed and compared to physiological data. The variation of the LV cavity volume over the cardiac cycle will also be discussed. [Preview Abstract] |
Monday, November 23, 2009 8:52AM - 9:05AM |
GE.00005: Fluid Structure Interaction simulation of heart prosthesis in patient-specific left-ventricle/aorta anatomies Trung Le, Iman Borazjani, Fotis Sotiropoulos In order to test and optimize heart valve prosthesis and enable virtual implantation of other biomedical devices it is essential to develop and validate high-resolution FSI-CFD codes for carrying out simulations in patient-specific geometries. We have developed a powerful numerical methodology for carrying out FSI simulations of cardiovascular flows based on the CURVIB approach (Borazjani, L. Ge, and F. Sotiropoulos, Journal of Computational physics, vol. 227, pp. 7587-7620 2008). We have extended our FSI method to overset grids to handle efficiently more complicated geometries e.g. simulating an MHV implanted in an anatomically realistic aorta and left-ventricle. A compliant, anatomic left-ventricle is modeled using prescribed motion in one domain. The mechanical heart valve is placed inside the second domain i.e. the body-fitted curvilinear mesh of the anatomic aorta. The simulations of an MHV with a left-ventricle model underscore the importance of inflow conditions and ventricular compliance for such simulations and demonstrate the potential of our method as a powerful tool for patient-specific simulations. [Preview Abstract] |
Monday, November 23, 2009 9:05AM - 9:18AM |
GE.00006: Volumetric velocity measurements on flows through heart valves Daniel Troolin, Devesh Amatya, Ellen Longmire Volumetric velocity fields inside two types of artificial heart valves were obtained experimentally through the use of volumetric 3-component velocimetry (V3V). Index matching was used to mitigate the effects of optical distortions due to interfaces between the fluid and curved walls. The steady flow downstream of a mechanical valve was measured and the results matched well with previously obtained 2D PIV results, such as those of Shipkowitz et al. (2002). Measurements upstream and downstream of a deformable silicone valve in a pulsatile flow were obtained and reveal significant three-dimensional features of the flow. Plots and movies will be shown, and a detailed discussion of the flow and various experimental considerations will be included. Reference: Shipkowitz, T, Ambrus J, Kurk J, Wickramasinghe K (2002) Evaluation technique for bileaflet mechanical valves. J. Heart Valve Disease. 11(2) pp. 275-282. [Preview Abstract] |
Monday, November 23, 2009 9:18AM - 9:31AM |
GE.00007: Fluid dynamics of aortic valve stenosis Zahra Keshavarz-Motamed, Nima Maftoon Aortic valve stenosis, which causes considerable constriction of the flow passage, is one of the most frequent cardiovascular diseases and is the most common cause of the valvular replacements which take place for around 100,000 per year in North America. Furthermore, it is considered as the most frequent cardiac disease after arterial hypertension and coronary artery disease. The objective of this study is to develop an analytical model considering the coupling effect between fluid flow and elastic deformation with reasonable boundary conditions to describe the effect of AS on the left ventricle and the aorta. The pulsatile and Newtonian blood flow through aortic stenosis with vascular wall deformability is analyzed and its effects are discussed in terms of flow parameters such as velocity, resistance to flow, shear stress distribution and pressure loss. Meanwhile we developed analytical expressions to improve the comprehension of the transvalvular hemodynamics and the aortic stenosis hemodynamics which is of great interest because of one main reason. To medical scientists, an accurate knowledge of the mechanical properties of whole blood flow in the aorta can suggest a new diagnostic tool. [Preview Abstract] |
Monday, November 23, 2009 9:31AM - 9:44AM |
GE.00008: Dynamic Energy Loss Characteristics in the Native Aortic Valve Choon Hwai Yap, Laksmi P. Dasi, Ajit P. Yoganathan Aortic Valve (AV) stenosis if untreated leads to heart failure. From a mechanics standpoint, heart failure implies failure to generate sufficient mechanical power to overcome energy losses in the circulation. Thus energy efficiency-based measures are direct measures of AV disease severity, which unfortunately is not used in current clinical measures of stenosis severity. We present an analysis of the dynamic rate of energy dissipation through the AV from direct high temporal resolution measurements of flow and pressure drop across the AV in a pulsatile left heart setup. Porcine AV was used and measurements at various conditions were acquired: varying stroke volumes; heart rates; and stenosis levels. Energy dissipation waveform has a distinctive pattern of being skewed towards late systole, attributed to the explosive growth of flow instabilities from adverse pressure gradient. Increasing heart rate and stroke volume increases energy dissipation, but does not alter the normalized shape of the dissipation temporal profile. Stenosis increases energy dissipation and also alters the normalized shape of dissipation waveform with significantly more losses during late acceleration phase. Since stenosis produces a departure from the signature dissipation waveform shape, dynamic energy dissipation analysis can be extended into a clinical tool for AV evaluation. [Preview Abstract] |
Monday, November 23, 2009 9:44AM - 9:57AM |
GE.00009: Fluid-structure interaction analysis of the flow through a stenotic aortic valve Hoda Maleki, Michel R. Labrosse, Louis-Gilles Durand, Lyes Kadem In Europe and North America, aortic stenosis (AS) is the most frequent valvular heart disease and cardiovascular disease after systemic hypertension and coronary artery disease. Understanding blood flow through an aortic stenosis and developing new accurate non-invasive diagnostic parameters is, therefore, of primarily importance. However, simulating such flows is highly challenging. In this study, we considered the interaction between blood flow and the valve leaflets and compared the results obtained in healthy valves with stenotic ones. One effective method to model the interaction between the fluid and the structure is to use Arbitrary Lagrangian-Eulerian (ALE) approach. Our two-dimensional model includes appropriate nonlinear and anisotropic materials. It is loaded during the systolic phase by applying pressure curves to the fluid domain at the inflow. For modeling the calcified stenotic valve, calcium will be added on the aortic side of valve leaflets. Such simulations allow us to determine the effective orifice area of the valve, one of the main parameters used clinically to evaluate the severity of an AS, and to correlate it with changes in the structure of the leaflets. [Preview Abstract] |
Monday, November 23, 2009 9:57AM - 10:10AM |
GE.00010: A study of the pulsatile flow and its interaction with rectangular leaflets Rene Ledesma, Roberto Zenit, Guillermo Pulos To avoid the complexity and limited understanding of the 3D pulsatile flow field through heart valves, a cardiac-like flow circuit and a test channel were designed to study the behavior of bidimensional leaflets made of hyperelastic materials. We study a simple 2D arrangement to understand the basic physics of the flow-leaflet interaction. Creating a periodic pressure gradient, measurements of leaflet deflection were obtained for different flow conditions, geometries and materials. Using PIV and Phase Locking techniques, we have obtained the leaflet motion and the time-dependent flow velocity fields. The results show that two dimensionless parameters determine the performance of a simple bi-dimensional valve, in accordance with the flow conditions applied: $\Pi _{1}$=f(sw)$^{1/2}$(E/$\rho )^{1/2}$ and $\Pi _{2}$=V/(2slw), where f is the pulsation frequency, V is the stroke volume, s, w and l are the dimensions on the leaftlet and E and $\rho $ are the elastic modulus and density of the material, respectively. Furthermore, we have identified the conditions for which the fluid stresses can be minimized. With these results we propose a new set of parameters to improve the performance of prosthetic heart valves and, in consequence, to reduce blood damage. [Preview Abstract] |
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