Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M24: Biofluids: Cardiovascular Disease II |
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Chair: Zahra Keshavarz-Motamed, MIT Room: 302 |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M24.00001: Fluid dynamics of coarctation of the aorta: analytical solution, \textit{in vitro} validation and \textit{in vivo} evaluation Zahra Keshavarz-Motamed Coarctation of the aorta (COA) is a congenital heart disease corresponding to a narrowing in the aorta. Cardiac catheterization is considered to be the reference standard for definitive evaluation of COA severity, based on the peak-to-peak trans-coarctation pressure gradient (PtoP TCPG) and instantaneous systolic value of trans-COA pressure gradient (TCPG). However, invasive cardiac catheterization may carry high risks given that undergoing multiple follow-up cardiac catheterizations in patients with COA is common. The objective of this study is to present an analytical description of the COA that estimates PtoP TCPG and TCPG without a need for high risk invasive data collection. Coupled Navier-Stokes and elastic deformation equations were solved analytically to estimate TCPG and PtoP TCPG. The results were validated against data measured in vitro (e.g., 90{\%} COA: TCPG: root mean squared error (RMSE)$=$ 3.93 mmHg; PtoP TCPG: RMSE$=$ 7.9 mmHg). Moreover, the estimated PtoP TCPG resulted from the suggested analytical description was validated using clinical data in twenty patients with COA (maximum RMSE: 8.3 mmHg). Very good correlation and concordance were found between TCPG and PtoP TCPG obtained from the analytical formulation and in vitro and in vivo data. The suggested methodology can be considered as an alternative to cardiac catheterization and can help preventing its risks. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M24.00002: Optimization of the assisted bidirectional Glenn for single ventricle palliation Alison Marsden, Jessica Shang, Mahdi Esmaily-Moghadam, Richard Figliola, Olaf Reinhartz, Tain-Yen Hsia For neonates with single ventricle physiology, a systemic-pulmonary shunt (e.g., a modified Blalock-Taussig shunt (mBTS)) is typically employed as an early-stage procedure in preparation for a later-stage bidirectional Glenn (BDG). Mortality rates with the mBTS are high, yet the BDG has poorer outcomes in neonates. The assisted bidirectional Glenn (ABG) augments the inadequate pulmonary flow associated with early BDG implementation in neonates through an additional shunt between the innominate artery and the superior vena cava (SVC). The shunt uses a nozzle to inject high-velocity flow to the SVC, elevating downstream pulmonary pressure. Previous simulations and animal studies verified feasibility and higher pulmonary flow rates. In numerical simulations, we explore shunt geometries and placements implanted into a 3D model of the aorta and pulmonary arteries, coupled with a lumped parameter network describing the remaining circulatory system. We seek an ABG shunt that optimizes hemodynamic variables such as pulmonary flow rate and oxygenation and constrains SVC pressure. The optimized ABG will be evaluated against the mBTS and the BDG in simulations and experiments. A successful implementation of the ABG would replace the mBTS and BDG procedures and reduce mortality rates. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M24.00003: Computational fluid dynamics study of commercially available stents inside an idealised curved coronary artery Winson Xiao Chen, Andrew Ooi, Nicholas Hutchins, Eric Poon, Vikas Thondapu, Peter Barlis Stent placement restores blood flow in diseased coronary arteries and is the standard treatment for obstructive coronary atherosclerosis. Analysis of the hemodynamic characteristics of stented arteries is essential for better understanding of the relationship between key fluid dynamic variables and stent designs. Previous computational studies have been limited to idealised stents in curved arterial segments or more realistic stents in straight segments. In clinical practice, however, it is often necessary to place stents in geometrically complex arterial curvatures. Thus, numerical simulations of the incompressible Navier--Stokes equations are carried out to investigate the effects of curvature on hemodynamics using detailed, commercially available coronary stents. The computational domain is a 3mm curved coronary artery model and simulations are conducted using a physiologically realistic inlet condition. The averaged flow rate is about 80 mL/min, similar to the normal human resting condition. The examination of hemodynamic parameters will assess the performance of several commercially available stents in curved arteries and identify regions that may be at risk for restenosis. It is anticipated that this information will lead to improvements in future stent design and deployment. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M24.00004: Lagrangian coherent structures and turbulence characteristics downstream of prosthetic aortic valves Marco D. de Tullio The flowfield through prosthetic heart valves is investigated by means of direct numerical simulations, considering the fully coupled fluid-structure interaction problem. Two different aortic valve models are modeled: a bileaflet mechanical and a biological one. In order to reveal fluid flow structures and to better understand the transport mechanics, Lagrangian coherent structures (LCS) are used. LCS are distinguished material surfaces that can be identified as boundaries to regions with dynamically distinct behavior, and are revealed as hypersurfaces that locally maximize the finite-time Lyapunov exponent (FTLE) fields. Post-processing the flow simulation data, first FTLE fields are calculated integrating dense meshes of Lagrangian particles backward in time, and then attracting LCS are extracted. A three-jet configuration is distinctive of bi-leaflet mechanical valves, with higher turbulent shear stresses immediately distal to the valve leaflets, while a jet-like flow emerges from the central orifice of bio-prosthetic valves, with high turbulent shear stresses occurring at the edge of the jet. Details of the numerical methodology along with a thorough analysis of the different flow structures developing during the cardiac cycle for the two configurations will be provided. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M24.00005: Experimental Comparison of the Hemodynamic Effects of Bifurcating Coronary Stent Implantation Techniques Melissa Brindise, Pavlos Vlachos Stent implantation in coronary bifurcations imposes unique effects to the blood flow patterns and currently there is no universally accepted stent deployment approach. Despite the fact that stent-induced changes can greatly alter clinical outcomes, no concrete understanding exists regarding the hemodynamic effects of each implantation method. This work presents an experimental evaluation of the hemodynamic differences between implantation techniques. We used four common stent implantation methods including the currently preferred one-stent provisional side branch (PSB) technique and the crush (CRU), Culotte (CUL), and T-stenting (T-PR) two-stent techniques, all deployed by a cardiologist in coronary models. Particle image velocimetry was used to obtain velocity and pressure fields. Wall shear stress (WSS), oscillatory shear index, residence times, and drag and compliance metrics were evaluated and compared against an un-stented case. The results of this study demonstrate that while PSB is preferred, both it and T-PR yielded detrimental hemodynamic effects such as low WSS values. CRU provided polarizing and unbalanced results. CUL demonstrated a symmetric flow field, balanced WSS distribution, and ultimately the most favorable hemodynamic environment. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M24.00006: Numerical modeling of the fetal blood flow in the placental circulatory system Alexander Shannon, Sergio Gallucci, Parisa Mirbod The placenta is a unique organ of exchange between the growing fetus and the mother. It incorporates almost all functions of the adult body, acting as the fetal lung, digestive and immune systems, to mention a few. The exchange of oxygen and nutrients takes place at the surface of the villous tree. Using an idealized geometry of the fetal villous trees in the mouse placenta, in this study we performed 3D computational analysis of the unsteady fetal blood flow, gas, and nutrient transport over the chorionic plate. The fetal blood was treated as an incompressible Newtonian fluid, and the oxygen and nutrient were treated as a passive scalar dissolved in blood plasma. The flow was laminar, and a commercial CFD code (COMSOL Multiphysics) has been used for the simulation. COMSOL has been selected because it is multi-physics FEM software that allows for the seamless coupling of different physics represented by partial differential equations. The results clearly illustrate that the specific branching pattern and the in-plane curvature of the fetal villous trees affect the delivery of blood, gas and nutrient transport to the whole placenta. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M24.00007: Hemodynamics in an Aorta with Bicuspid and Trileaflet Valves Anvar Gilmanov, Fotis Sotiropoulos Bicuspid aortic valve (BAV) is a congenital heart defect that has been associated with serious aortopathies, such as ascending aortic aneurysm, aortic stenosis, aortic regurgitation, infective endocarditis, aortic dissection, calcific aortic valve and dilatation of ascending aorta. Two main hypotheses - the genetic and the hemodynamic are discussed in literature to explain the development and progression of aortopathies in patients with BAV. In this study we seek to investigate the possible role of hemodynamic factors as causes of BAV-associated aortopathy. We employ the Curvilinear Immersed Boundary (CURVIB) method coupled with an efficient thin-shell finite element (TS-FE) formulation for tissues to carry out fluid-structure interaction simulations of a healthy tri-leaflet aortic valve (TAV) and a BAV placed in the same anatomic aorta. The computed results reveal major differences between the TAV and BAV flow patterns. These include: the dynamics of the aortic valve vortex ring formation and break up; the large scale flow patterns in the ascending aorta; and the shear stress magnitude on the aortic wall. The computed results are in qualitative agreement with in vivo Magnetic Resonance Imaging (MRI) data and suggest that the linkages between BAV aortopathy and hemodynamics deserve further investigation. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M24.00008: A numerical investigation of a simplified human birth model Roseanna Pealatere, Alexa Baumer, Lisa Fauci, Megan C. Leftwich This work uses simplified models and numerical computations to explore the effects of both the fetal velocity and the viscosity of the surrounding fluid on the forces associated with human birth. The numerical results are compared with the results of an experimental model representing the fetus moving through the birth canal using a rigid cylinder (fetus) that moves at a constant velocity through the center of a passive elastic tube (birth canal). The entire system is immersed in highly viscous fluid. Due to low Reynolds’ number, the Stokes equations can be used to describe the relationship between velocity and forces in the system. The mathematical model uses the method of regularized Stokeslets to estimate the pulling force necessary to move the rigid inner cylinder at a constant velocity. The elastic tube through which the rigid cylinder passes is constructed by a discrete network of Hookean springs, with macroscopic elasticity matched to the tube used in the physical experiment. More complex geometries as well as peristaltic activation of the elastic tube can be added to the model to provide more insight into the relationship between force and velocity during human birth. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M24.00009: Tubular Heart Pumping Mechanisms in Ciona Intestinalis Nicholas Battista, Laura Miller In vertebrate embryogenesis, the first organ to form is the heart, beginning as a primitive heart tube. However, many invertebrates have tubular hearts from infancy through adulthood. Heart tubes have been described as peristaltic and impedance pumps. Impedance pumping assumes a single actuation point of contraction, while traditional peristalsis assumes a traveling wave of actuation. In addition to differences in flow, this inherently implies differences in the conduction system. It is possible to transition from pumping mechanism to the other with a change in the diffusivity of the action potential. In this work we consider the coupling between the fluid dynamics and electrophysiology of both mechanisms, within a basal chordate, the tunicate. Using CFD with a neuro-mechanical model of tubular pumping, we discuss implications of the both mechanisms. Furthermore, we discuss the implications of the pumping mechanism on evolution and development. [Preview Abstract] |
Tuesday, November 24, 2015 9:57AM - 10:10AM |
M24.00010: Effect of Trabeculae on the Hemodynamics of an Embryonic Left Ventricle Vijay Vedula, Juhyun Lee, Tzung Hsiai, Alison Marsden The left ventricular (LV) endocardium is not smooth, but has ``trabeculae'' protruding into the LV cavity. Recent studies have indicated that trabeculae significantly influence LV hemodynamics by enhancing the diastolic penetration depth of inflow and facilitating a better apical systolic washout. However, it remains unclear how the role of hemodynamics modulates the initiation of trabeculae during cardiac morphogenesis. While such an assessment of mammalian heart models is hampered by the prolonged duration of cardiac development and complexity of surrounding internal organs, embryonic zebrafish is a genetically tractable model for investigating cardiac morphogenesis. We employ a novel light-sheet fluorescent microscopy to extract 4D LV models of zebrafish and develop an ALE-based moving domain CFD solver to perform flow simulations and extract quantitative data related to flow velocities and pressure gradients. We will compare near-wall flow dynamics between the wild type zebrafish (with trabeculae) and the cloche mutant lines that fail to develop trabeculae, to provide new insights into the flow-induced mechano-transduction relevant to the initiation of trabeculae during cardiac morphogenesis. [Preview Abstract] |
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