Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session A15: Bio: Cardiovascular Interventions |
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Chair: Alison Marsden, Stanford University Room: E143/144 |
Sunday, November 20, 2016 8:00AM - 8:13AM |
A15.00001: Patient-specific modeling of the Assisted Bidirectional Glenn (ABG) Jessica Shang, Mahdi Esmaily-Moghadam, Richard Figliola, Tain-Yen Hsia, Alison Marsden The Assisted Bidirectional Glenn (ABG) is proposed as an early-stage palliative procedure for single ventricle neonates. The ABG augments the pulmonary flow of the Bidirectional Glenn (BDG) with a secondary high-velocity flow through a nozzle-like shunt between the innominate artery and the superior vena cava (SVC). The ABG would provide a superior cavopulmonary connection than the systemic-pulmonary shunt that is typically employed as a stage-I procedure (e.g., a modified Blalock-Taussig shunt) and would address the low pulmonary flow associated with the BDG. Following simulations in vitro and in silico that show the ABG successfully increased pulmonary flows in idealized models, we implemented the ABG in several patient-specific models coupled to a lumped parameter network tuned to clinical values for each patient. The ABG performed similarly across different patients; compared to the BDG, the pulmonary flow increased $\sim$20\% with a similar increase in the SVC pressure. The performance of the ABG was the most sensitive to nozzle outlet area, compared to nozzle inlet area and location of the shunt anastomosis. The study verified that the ABG benefits a range of patients and identified key parameters for further optimization of the ABG. [Preview Abstract] |
Sunday, November 20, 2016 8:13AM - 8:26AM |
A15.00002: Shape Optimization of the Assisted Bi-directional Glenn surgery for stage-1 single ventricle palliation Aekaansh Verma, Jessica Shang, Mahdi Esmaily-Moghadam, Kwai Wong, Alison Marsden Babies born with a single functional ventricle typically undergo three open-heart surgeries starting as neonates. The first of these stages (BT shunt or Norwood) has the highest mortality rates of the three, approaching 30{\%}. Proceeding directly to a stage-2 Glenn surgery has historically demonstrated inadequate pulmonary flow (PF) {\&} high mortality. Recently, the Assisted Bi-directional Glenn (ABG) was proposed as a promising means to achieve a stable physiology by assisting the PF via an 'ejector pump' from the systemic circulation. We present preliminary parametrization and optimization results for the ABG geometry, with the goal of increasing PF. To limit excessive pressure increases in the Superior Vena Cava (SVC), the SVC pressure is included as a constraint. We use 3-D finite element flow simulations coupled with a single ventricle lumped parameter network to evaluate PF {\&} the pressure constraint. We employ a derivative free optimization method- the Surrogate Management Framework, in conjunction with the OpenDIEL framework to simulate multiple simultaneous evaluations. Results show that nozzle diameter is the most important design parameter affecting ABG performance. The application of these results to patient specific situations will be discussed. [Preview Abstract] |
Sunday, November 20, 2016 8:26AM - 8:39AM |
A15.00003: Modeling the Mitral Valve Alexander Kaiser The mitral valve is one of four valves in the human heart. The valve opens to allow oxygenated blood from the lungs to fill the left ventricle, and closes when the ventricle contracts to prevent backflow. The valve is composed of two fibrous leaflets which hang from a ring. These leaflets are supported like a parachute by a system of strings called chordae tendineae. In this talk, I will describe a new computational model of the mitral valve. To generate geometry, general information comes from classical anatomy texts and the author's dissection of porcine hearts. An MRI image of a human heart is used to locate the tips of the papillary muscles, which anchor the chordae tendineae, in relation to the mitral ring. The initial configurations of the valve leaflets and chordae tendineae are found by solving solving an equilibrium elasticity problem. The valve is then simulated in fluid (blood) using the immersed boundary method over multiple heart cycles in a model valve tester. We aim to identify features and mechanisms that influence or control valve function. [Preview Abstract] |
Sunday, November 20, 2016 8:39AM - 8:52AM |
A15.00004: Effect of mitral valve prosthesis design and orientation on intraventricular flow and blood stasis Karen May-Newman, J Campos, R Montes, V Ramesh, J Moon, C Reider, P Martinez-Legazpi, J Bermejo, Lorenzo Rossini, Juan C del Alamo Abnormal blood flow patterns are linked with thromboembolism (TE), especially in the presence of medical devices such as mitral valve prostheses (MVP). We performed PIV on a customized silicone left ventricle (LV) in a mock circulatory loop. We measured the velocity field in the long-axis midplane for 3 different MVP: a porcine bioprosthesis (BP), a tilting disk valve in two orientations: towards the LV lateral (TD-L) or the anterior wall (TD-A), and a bileaflet valve with anti-anatomical orientation (BL). Diastolic LV vortices were tracked and related to measures of blood stasis based on LV residence time. The BP and the TD-L produced flow patterns similar to those measured in patients. The TD-A showed a complete reversal of diastolic vortices. The BL design had increased apical blood stasis, which may lead to increased TE risk. [Preview Abstract] |
Sunday, November 20, 2016 8:52AM - 9:05AM |
A15.00005: Fluid-structure interaction in the left ventricle of the human heart coupled with mitral valve Valentina Meschini, Marco Donato De Tullio, Giorgio Querzoli, Roberto Verzicco In this paper Direct Numerical Simulations (DNS), implemented using a fully fluid-structure interaction model for the left ventricle, the mitral valve and the flowing blood, and laboratory experiments are performed in order to cross validate the results. Moreover a parameter affecting the flow dynamics is the presence of a mitral valve. We model two cases, one with a natural mitral valve and another with a prosthetic mechanical one. Our aim is to understand their different effects on the flow inside the left ventricle in order to better investigate the process of valve replacement. We simulate two situations, one of a healthy left ventricle and another of a failing one. While in the first case the flow reaches the apex of the left ventricle and washout the stagnant fluid with both mechanical and natural valve, in the second case the disturbance generated by the mechanical leaflets destabilizes the mitral jet, thus further decreasing its capability to penetrate the ventricular region and originating heart attack or cardiac pathologies in general. [Preview Abstract] |
Sunday, November 20, 2016 9:05AM - 9:18AM |
A15.00006: Platelet activation through a Bi-leaflet mechanical heart valve Mohammadali Hedayat, Iman Borazjani Platelet activation is one of the major drawbacks of the Mechanical Heart Valves (MHVs) which can increase the risk of thrombus formation in patients. The platelet activation in MHVs can be due to the abnormal shear stress during the systole, the backward leakage flow during the diastole, and the flow through the hinge region. We investigate the contribution of each of the above mechanism to the activation of platelets in MHVs by performing simulations of the flow through the MHV and in the hinge region. The large scale heart valve simulations are performed in a straight aorta using a sharp interface curvilinear immersed boundary method along with a strong-coupling algorithm under physiological flow conditions. In addition, in order to perform the simulation of hinge region the flow field boundary conditions are obtained from the largescale simulations during a whole cardiac cycle. In order to investigate the role of hinge flow on platelet activation in MHVs, a 23mm St. Jude Medical Regent valve hinge with three different gap sizes is tested along with different platelet activation models to ensure the consistency of our results with different activation models. We compare the platelet activation of the hinge region against the bulk of the flow during one cardiac cycle. [Preview Abstract] |
Sunday, November 20, 2016 9:18AM - 9:31AM |
A15.00007: Influence of surgical implantation angle of left ventricular assist device outflow graft and management of aortic valve opening on the risk of stroke in heart failure patients V. Keshav Chivukula, Patrick McGah, Anthony Prisco, Jennifer Beckman, Nanush Mokadam, Claudius Mahr, Alberto Aliseda Flow in the aortic vasculature may impact stroke risk in patients with left ventricular assist devices (LVAD) due to severely altered hemodynamics. Patient-specific 3D models of the aortic arch and great vessels were created with an LVAD outflow graft at 45, 60 and $90^o$ from centerline of the ascending aorta, in order to understand the effect of surgical placement on hemodynamics and thrombotic risk. Intermittent aortic valve opening (once every five cardiac cycles) was simulated and the impact of this residual native output investigated for the potential to wash out stagnant flow in the aortic root region. Unsteady CFD simulations with patient-specific boundary conditions were performed. Particle tracking for 10 cardiac cycles was used to determine platelet residence times and shear stress histories. Thrombosis risk was assessed by a combination of Eulerian and Lagrangian metrics and a newly developed thrombogenic potential metric. Results show a strong influence of LVAD outflow graft angle on hemodynamics in the ascending aorta and consequently on stroke risk, with a highly positive impact of aortic valve opening, even at low frequencies. Optimization of LVAD implantation and management strategies based on patient-specific simulations to minimize stroke risk will be presented [Preview Abstract] |
Sunday, November 20, 2016 9:31AM - 9:44AM |
A15.00008: Three-dimensional Computational Simulation and In-vitro Experiments for Assessing Radiocephalic Wrist Arteriovenous Fistulas Ryungeun Song, Sun Cheol Park, Hyun Kyu Kim, Jinkee Lee A radio-cephalic arteriovenous fistula (RC-AVF) is the best choice for achieving vascular access (VA) for hemodialysis, but this AVF has high rates of early failure depending on the vessel condition. The high wall shear stress (WSS) contributes to VA failures due to plaque rupture, thrombosis, etc. Thus, we have used a low-Re k-$\varepsilon $ turbulence based CFD model combined with an in-vitro experimental approach to evaluate the WSS distribution and to minimize its effects under several conditions. The properties considered in this study were non-Newtonian flow characteristics, complete cardiac pulse cycle, and distention of blood vessels. The computational domain was designed for arteriovenous end-to-side anastomosis based on anastomosis angles of 45\textdegree , 90\textdegree , and 135\textdegree . For experiment the digital domains were converted into 3D artificial RC-AVF via poly(dimethylsiloxame) (PDMS) and 3D printing technology. The micro-particle image velocimetry ($\mu $-PIV) was used to measure the velocity field within the artificial blood vessel. The results showed that the largest anastomosis angle (135\textdegree ) resulted in lower WSS, which would help reduce AVF failures. This research would provide the future possibility of using the proposed method to reduce in-vivo AVF failure for various conditions in each patient. [Preview Abstract] |
Sunday, November 20, 2016 9:44AM - 9:57AM |
A15.00009: Wall Shear Stress Restoration in Dialysis Patient’s Venous Stenosis: Elucidation via 3D CFD and Shape Optimization S. M. Javid Mahmoudzadeh Akherat, Kevin Cassel, Mary Hammes, Michael Boghosian Venous stenosis developed after the growth of excessive neointimal hyperplasia (NH) in chronic dialysis treatment is a major cause of mortality in renal failure patients. It has been hypothesized that the low wall shear stress (WSS) triggers an adaptive response in patients' venous system that through the growth of neointimal hyperplastic lesions restores WSS and transmural pressure, which also regulates the blood flow rate back to physiologically acceptable values which is violated by dialysis treatment. A strong coupling of three-dimensional CFD and shape optimization analyses were exploited to elucidate and forecast this adaptive response which correlates very well topographically with patient-specific clinical data. Based on the framework developed, a medical protocol is suggested to predict and prevent dialysis treatment failure in clinical practice. [Preview Abstract] |
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