Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session A13: Biofluids: Cardiovascular: Pathological Flow and Intervention |
Hide Abstracts |
Chair: Alison Marsden, University of California, San Diego Room: 316 |
Sunday, November 20, 2011 8:00AM - 8:13AM |
A13.00001: Virtual Cardiac Surgery Using CFD: Application to Septal Myectomy in Obstructive Hypertrophic Cardiomyopathy Vijay Vedula, Rajat Mittal, Theodore Abraham Obstructive hypertrophic cardiomyopathy (HOCM) is characterized by ventricular wall thickening, diastolic dysfunction, and dynamic outflow tract obstruction, all of which strongly influence the vortex dynamics and pressure distribution in the left ventricle (LV). Severe cases of HCM are usually managed through septal myectomy where the surgeon resects the hypertrophic mass. Surgeons currently try to remove as much tissue as possible in order to optimize the post surgical result. However, excessive debulking increases the chance of ventricular septal defects, bundle branch block or complete heart block, and aneurysmal septal thinning. On the other hand, insufficient tissue removal also leads to unsatisfactory outcomes in terms of reduction of outflow tract pressure gradient. Knowing how much muscle to remove and where to remove it from could reduce the likelihood of complications and suboptimal outcomes. In the present study, we employ an immersed boundary solver to model the effect of septal myectomy for ventricles with HOCM and demonstrate the potential of such an approach for surgical planning. [Preview Abstract] |
Sunday, November 20, 2011 8:13AM - 8:26AM |
A13.00002: Investigation of Systolic Heart Murmurs with Computational Hemo-Acoustic Modeling Jung Hee Seo, Rajat Mittal, Theodore Abraham Detection and analysis of heart murmurs generated by abnormal blood flows can be used as a low cost, non-invasive routine screening for the heart disease. Phonocardiography is an approach which combines electronic sound detection with automated signal analysis for detecting abnormal heart murmurs but the current approach relies primarily on empirical statistical correlations and ignores the underlying physics of flow-induced sound generation and propagation. In the present study, we investigate the characteristics and generation mechanism of systolic heart murmurs associated with the obstructive hypertrophic cardiomyopathy (HOCM) using the computational fluid dynamics and acoustics modelings. The hemodynamic flow field in left ventricle outflow tract is simulated with the immersed boundary, incompressible Navier-Stokes solver, and the sound generated by the blood flow is modeled by the linearized perturbed compressible equations. The propagation of the sound through the surrounding tissues is also modeled by the linear structural wave equations. The simulated murmurs are analyzed for the timing, frequency, and intensity and the correlation with the hemodynamics is closely investigated to identify the source mechanisms. [Preview Abstract] |
Sunday, November 20, 2011 8:26AM - 8:39AM |
A13.00003: Analysis of intracardiac flows for Diastolic heart dysfunction Rajat Mittal, Xudong Zheng, Vijay Vedula, Theodore Abraham Diastolic dysfunction (DD) is a common finding in a variety of cardiac diseases including hypertension, coronary disease and cardiomyopathy. Its prevalence increases with age and it manifests as incomplete or/and delayed ventricular relaxation and a compensatory stronger atrial contraction. DD is often associated with heart failure and contributes greatly to morbidity and hospitalizations especially in the elderly. In the current study, three-dimensional Navier-Stokes simulations are employed to investigate intracardiac flow behavior in normal and diseased hearts with DD. The endocardial surface of the left ventricle is represented by a generic simplified prolate-spheroid and the wall motion is driven by the ventricular volume change. Diastolic dysfunction in the heart is modeled by prescribing different E/A filling ratios. The dominant flow features, such as vortices and swirling structures and associated Eulerian and Lagrangian metrics are examined to gain insights into the flow physics of this disease. [Preview Abstract] |
Sunday, November 20, 2011 8:39AM - 8:52AM |
A13.00004: Multiscale modeling and simulation of blood flow in coronary artery bypass graft surgeries Sethuraman Sankaran, Mahdi Esmaily Moghadam, Andy Kahn, Alison Marsden We present a computational framework for modeling and simulation of blood flow in patients who undergo coronary artery bypass graft (CABG) surgeries. We evaluate the influence of shape on the homeostatic state, cardiac output, and other quantities of interest. We present a case study on a patient with multiple CABG. We build a patient-specific model of the blood vessels comprised of the aorta, vessels branching from the top of the aorta (brachiocephalic artery and carotids) and the coronary arteries, in addition to bypass grafts. The rest of the circulatory system is modeled using lumped parameter 0D models comprised of resistances, compliances, inertances and elastance. An algorithm is presented that computes these parameters automatically given constraints on the flow. A Finite element framework is used to compute blood flow and pressure in the 3D model to which the 0D code is coupled at the model inlets and outlets. An adaptive closed loop BC is used to capture the coupling of the various outlets of the model with inlets, and is compared with a model with fixed inlet BC. We compare and contrast the pressure, flowrate, coronary perfusion, and PV curves obtained in the different cases. Further, we compare and contrast quantities of interest such as wall shear stress, wall shear stress gradients and oscillatory shear index for different surgical geometries and discuss implications of patient-specific optimization. [Preview Abstract] |
Sunday, November 20, 2011 8:52AM - 9:05AM |
A13.00005: Fluid Structure Interaction Simulations of Pediatric Ventricular Assist Device Operation Chris Long, Alison Marsden, Yuri Bazilevs Pediatric ventricular assist devices (PVADs) are used for mechanical circulatory support in children with failing hearts. They can be used to allow the heart to heal naturally or to extend the life of the patient until transplant. A PVAD has two chambers, blood and air, separated by a flexible membrane. The air chamber is pressurized, which drives the membrane and pumps the blood. The primary risk associated with these devices is stroke or embolism from thrombogenesis. Simulation of these devices is difficult due to a complex coupling of two fluid domains and a thin membrane, requiring fluid-structure interaction modeling. The goal of this work is to accurately simulate the hemodynamics of a PVAD. We perform FSI simulations using an Arbitrary Lagrangian-Eulerian (ALE) finite element framework to account for large motions of the membrane and the fluid domains. The air, blood, and membrane are meshed as distinct subdomains, and a method for non-matched discretizations at the fluid-structure interface is presented. The use of isogeometric analysis to model the membrane mechanics is also discussed, and the results of simulations are presented. [Preview Abstract] |
Sunday, November 20, 2011 9:05AM - 9:18AM |
A13.00006: Device specific analysis of neonatal aortic outflow cannula jet flows for improved cardiopulmonary bypass hemodynamics Prahlad Menon, Fotis Sotiropoulos, Akif Undar, Kerem Pekkan Hemodynamically efficient aortic outflow cannulae can provide high blood volume flow rates at low exit force during extracorporeal circulation in pediatric or neonatal cardiopulmonary bypass repairs. Furthermore, optimal hemolytic aortic insertion configurations can significantly reduce risk of post-surgical neurological complications and developmental defects in the young patient. The methodology and results presented in this study serve as a baseline for design of superior aortic outflow cannulae based on a novel paradigm of characterizing jet-flows at different flow regimes. \textit{In-silico} evaluations of multiple cannula tips were used to delineate baseline hemodynamic performance of the popular pediatric cannula tips in an experimental cuboidal test-rig, using PIV. High resolution CFD jet-flow simulations performed for various cannula tips in the cuboidal test-rig as well as \textit{in-vivo} insertion configurations have suggested the existence of optimal surgically relevant characteristics such as cannula outflow angle and insertion depth for improved hemodynamic performance during surgery. Improved cannula tips were designed with internal flow-control features for decreased blood damage and increased permissible flow rates. [Preview Abstract] |
Sunday, November 20, 2011 9:18AM - 9:31AM |
A13.00007: High Order Large Eddy Simulation (LES) of Flow in Idealized Total Cavopulmonary Connection (TCPC) Yann Delorme, Kameswararao Anupindi, Dinesh Shetty, Anna-Elodie Kerlo, Jun Chen, Mark Rodefeld, Steven Frankel Irregular, transitional, and chaotic flow fields have been observed in previous experimental studies of the TCPC. Low-order numerical methods have been shown to be unable to capture these unsteady flow structures when compared to experimental flow studies. A high-order incompressible LES code is combined with a recent Immersed Boundary Method (IBM) to enable structured Cartesian grids to represent the TCPC geometry. Validation studies for canonical flows and recent PIV data for the TCPC case are shown. Analysis of the instantaneous vortical structure and mean statistics are presented to further elucidate the complex flow patterns and wall shear stress distributions. Recent studies proved that mechanical support through a Viscous Impeller Pump (VIP) can improve TCPC hemodynamics by increasing the pressure and the blood flow through the lungs. The inclusion of this novel VIP to power the Fontan circulation is also studied with further comparisons to PIV and HQ data. Finally, dynamic mode decomposition is used to study TCPC flow modes and particle transport is considered to assess thrombosis potential. [Preview Abstract] |
Sunday, November 20, 2011 9:31AM - 9:44AM |
A13.00008: Stereoscopic PIV of Powered Fontan Hemodynamics in Idealized Total Cavopulmonary Connection (TCPC) Anna-Elodie Kerlo, Mark Rodefeld, Steven Frankel, Jun Chen Stereoscopic Particle Image Velocimetry (SPIV) measurements are presented in an idealized TCPC geometry powered by a novel Viscous Impeller Pump (VIP) designed to provide mechanical assist to univentricular Fontan circulations. Instantaneous flow patterns and mean flow statistics are reported to provide insight into flow structure and wall shear stress. Dynamic mode decomposition is applied to SPIV data to extract relevant modes from the flow without and with the VIP present and operating. Previous experimental and computational studies showed excellent hemodynamic performance of the VIP: it stabilizes the four-way flow pattern without risk of obstruction to flow and augments flow in ideal pressure range (0-10 mmHg). This holds out the promises of providing temporary support for patients with failing Fontan circulations and ultimately reducing the 3-stage Fontan surgical procedures to one. Our SPIV data help to elaborate on VIP performance by analyzing detailed unsteady flow features and serve as a database for more advanced computational studies such as large eddy simulation. [Preview Abstract] |
Sunday, November 20, 2011 9:44AM - 9:57AM |
A13.00009: Elevated Shear Stress in Arteriovenous Fistulae: Is There Mechanical Homeostasis? Patrick McGah, Daniel Leotta, Kirk Beach, Alberto Aliseda Arteriovenous fistulae are created surgically to provide access for dialysis in patients with renal failure. The current hypothesis is that the rapid remodeling occurring after the fistula creation is in part a process to restore the mechanical stresses to some preferred level (i.e. mechanical homeostasis). Given that nearly 50\% of fistulae require an intervention after one year, understanding the altered hemodynamic stress is important in improving clinical outcomes. We perform numerical simulations of four patient-specific models of functioning fistulae reconstructed from 3D Doppler ultrasound scans. Our results show that the vessels are subjected to `normal' shear stresses away from the anastomosis; about 1 Pa in the veins and about 2.5 Pa in the arteries. However, simulations show that part of the anastomoses are consistently subjected to very high shear stress ($>$10Pa) over the cardiac cycle. These elevated values shear stresses are caused by the transitional flows at the anastomoses including flow separation and quasiperiodic vortex shedding. This suggests that the remodeling process lowers shear stress in the fistula but that it is limited as evidenced by the elevated shear at the anastomoses. This constant insult on the arterialized venous wall may explain the process of late fistula failure in which the dialysis access become occluded after years of use. [Preview Abstract] |
Sunday, November 20, 2011 9:57AM - 10:10AM |
A13.00010: Effects of Mixing on the Conductance Measurements of Artery Cross-Section Area Qing Hao, Hyo Won Choi, Ghassan Kassab Turbulent dispersive mixing occurs during injection of saline into artery for the conductance catheter measurement of lumen cross section area (CSA). The objective of present study is to evaluate the accuracy of conductance catheter measurement in relation to dispersion. Computational fluid dynamics (CFD) simulations were performed to describe fluid flow, mass and electric field in artery with saline injected through different catheters and for different injection times. The simulation results showed that axial velocity profiles in all cases can reach stable after 0.5 sec and a recirculation zone exists distal to the saline injection site for Craya-Curtet number below critical value (0.7-0.98). A stable mixture ratio of saline and blood was reached in a distance of 8 artery diameters downstream of saline injection site. The results also showed that the accuracy of conductance catheter is affected by injection time, artery size, and conductance catheter location. The mixing ratio of saline and blood was shown to be a major factor affecting the accuracy of the conductance catheter measurement of CSA. A modification of electrical conductivity according to the mixing ratio improved the accuracy of conductance measurements and decreased the error to an acceptable level ($<$10{\%}) regardless of the vessel size and injection flow rate. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700