Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session Q17: Biological fluid dynamics: Cardiac Flows |
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Chair: Oscar Flores, University Carlos III de Madrid Room: Georgia World Congress Center B304 |
Tuesday, November 20, 2018 12:50PM - 1:03PM |
Q17.00001: In vitro assessment of bioprosthetic valve performance in healthy and diseased right ventricular outflow tracts using magnetic resonance velocimetry Nicole Schiavone, Christopher Elkins, Doff McElhinney, John K. Eaton, Alison L. Marsden The congenital heart defect Tetralogy of Fallot (ToF) affects 1 in every 2500 newborns annually and requires surgical repair of the right ventricular outflow tract (RVOT) and subsequent placement of an artificial pulmonary valve. The longevity of these valves is highly variable and complications from ToF lead to large disparities in RVOT anatomy among patients. This work aims to assess the performance of bioprosthetic pulmonary valves in healthy and diseased RVOT geometries using magnetic resonance velocimetry. Two 3D-printed geometries were analyzed: an idealized case based on healthy subjects aged 11 to 13 and a diseased case with a 150% dilation in vessel diameter downstream of the valve. Each geometry was studied with two valve orientations: one with a valve leaflet opening posterior, which is the native pulmonary valve position, and one with a valve leaflet opening anterior. Flow features, including vortex formation and stagnation regions, are shown to be drastically different between the RVOT geometries and valve orientations. For example, in the diseased geometry, changing the valve orientation alters the jet angle at systole by 20 degrees and reduces recirculating flow around the valve throughout the cardiac cycle. |
Tuesday, November 20, 2018 1:03PM - 1:16PM |
Q17.00002: A Dual State-Parameter Ensemble Kalman Filter for Patient-Specific Cardiovascular Modeling Daniel Canuto, Yi-Jui Chang, Jeff Eldredge, Erik Dutson, Peyman Benharash Developing models for patient-specific healthcare usually requires extensive parameter tuning to produce data that adequately matches an individual's clinical measurements. This tuning process is frequently non-trivial: the parameter set is usually large, and the parameters often have nonlinear relationships with both model predictions and each other. Adjusting the parameters in an ad-hoc way is therefore quite costly and requires significant end-user expertise. To avoid this hurdle, this work develops and discusses an ensemble Kalman filter (EnKF) for automated parameter estimation in a reduced-order cardiovascular model. Specifically, we construct a dual EnKF to independently filter the state and parameter vectors. The performance of the estimator is demonstrated using measurements from both healthy and pathological patients, and attention is given to methods for improving its robustness. |
Tuesday, November 20, 2018 1:16PM - 1:29PM |
Q17.00003: Computational modeling of hemodynamics and blood washout in the patient-specific left atrial appendages Chuanxin Ni, Jung-Hee Seo, Rajat Mittal The left atrial appendage (LAA) is a small chamber-like organ connected to the left atrium (LA). Studies have shown that this structure is implicated in thrombus formation and thromboembolic events for patients with atrial fibrillations. However, due to its highly complex and variable shape, the blood flow patterns and the mechanism of thrombogenesis inside the LAA are poorly understood. The aim of this study is to analyze the hemodynamics inside patient-specific LA/LAAs via computational fluid dynamics (CFD) modeling and to understand the potential for thrombus formation in the LAA. Patient-specific LA/LAA geometries are derived from high-resolution CT scans and the blood flowrate profiles at the mitral annulus are obtained from ultrasound Doppler measurements. Direct numerical simulation is carried out using a sharp-interface immersed boundary method. An Eulerian transport equation for the blood residence time is also solved inside the fluid domain to investigate the blood transportation and coagulation potential in the LAA. In this study, several patient-specific cases with different LAA shapes and heart conditions are considered and the blood flow patterns and washout in the LAA are compared for these cases. |
Tuesday, November 20, 2018 1:29PM - 1:42PM |
Q17.00004: Reduced order modeling of the circulatory system hemodynamics for 0D-3D coupled simulations Chenwei Meng, Mahdi Esmaily Moghadam Lower dimensional lumped parameter networks (LPN) coupled to 3D models provides a relatively accurate method for capturing global hemodynamics of the circulatory system at an affordable cost. In this method, the major vessels are fully solved in a 3D model of patient anatomy whereas the rest of the circulatory system is often modeled with a 0D LPN. Provided a set of clinical measurements, tuning components in the LPN poses a major challenge in this approach as it requires adjusting model parameters (LPN 0D components) to minimize the difference between model output and clinical measurements. This optimization procedure can be costly as it requires simulating the 3D domain at each iteration. In this study, we offer an alternative approach, where a simplified 0D circuit model replaces the 3D model, thereby reducing the cost of the tuning process at each iteration to simulating an inexpensive 0D-0D coupled model. To construct this simplified model, we developed a separate optimization algorithm that is tailored to this problem. We demonstrate the reasonable accuracy and computational cost efficiency of our approach by comparing it to the standard 3D/0D procedure. |
Tuesday, November 20, 2018 1:42PM - 1:55PM |
Q17.00005: Evaluation of blood-stasis in the left atrium using patient-specific CFD Oscar Flores, Lorenzo Rossini, Alejandro Gonzalo, Davis Vigneault, Andrew M Kahn, Manuel García-Villalba, Eliot McVeigh, Juan C Del Alamo Patients with atrial fibrillation (AF) present increased risk of systemic embolism and stroke, and are usually treated with anticoagulant therapies. Given the risk of adverse effects of these therapies, it is necessary to develop personalized quantitative tools to predict the risk of LA thrombogenesis. To that end, a computational fluid dynamics model of patient-specific LA hemodynamics has been developed, where blood stasis and thrombogenesis risk is estimated with the blood residence time (RT). The time-dependent LA geometry was obtained from computed tomography scans. In order to study the effect of atrial contractility and anatomy, simulations were performed for N=4 patients (including one with AF), considering both moving and stationary LA walls. In all subjects blood RT was highest inside the left atrial apendage (LAA). The averaged RT inside the LAA correlated inversely with LAA ejection fractions across different subjects. Furthermore, blood RT in the LAA was markedly higher in the patient with AF. However, the RT for each patient showed a weak dependence on LA wall motion, suggesting that additional factors such as atrial geometry may play a role in governing LA blood stasis. |
Tuesday, November 20, 2018 1:55PM - 2:08PM |
Q17.00006: A multi-way coupled model for the left-heart: Fluid-Structure-Electrophysiology interaction (FSEI). Francesco Viola, Valentina Meschini, Roberto Verzicco During one day the human heart beats approximately 100,000 times. Each beat is triggered by specialized pacemaker cells that generate rhythmical electrical impulses rapidly propagating through the heart walls, stimulating myocytes contraction and, in turn, pumping blood. When this system functions normally the four heart chambers are well synchronized. In contrast, damages in the conductive system can alter the beating heart rhythm or modify the normal sequence of contraction of ventricles and atria thus reducing the pumping effectiveness. In this study we present a computational model for unprecedented simulations of the left heart in physiological and pathological conditions. To this aim, a multi-way coupling between the network of conductive fibers (monodomain and bidomain models), the myocardium deformation (structural solver) and the produced hemodynamics (fluid solver) is needed. The resulting multi-physics model is then employed to study the physiological hemodynamics in the whole left heart, including atrium, aorta and ventricle with aortic/mitral valves. We also investigate how the heart pumping efficiency, in terms of ejection fraction and atrium/ventricle synchronization, is affected by a modification of the electrical conduction system or pacing location. |
Tuesday, November 20, 2018 2:08PM - 2:21PM |
Q17.00007: Can difference in patient coronary flow waveform alter patients' outcomes? Eric Poon, Vikas Thondapu, Peter Barlis, Andrew Ooi, Shuang Zhu The human coronaries system is a sophisticated flow network with complicated haemodynamic environments. At the core, our heart periodically supplies blood to maintain functionalities of our bodies. These periodic blood flow movements change from person to person. Yet despite increasing awareness on the pulsating flow environment, typical computational fluid dynamics (CFD) studies often rely on population-specific pulsatile waveforms. In this study, we investigate the impacts of different pulsatile waveforms of the left coronary arteries (with identical mean flow rate of 1.3 cc/s) on the recirculation environments near a scaffolded coronary segment. Under the effect of pulsatile coronary flow, recirculation environments are, in general, most pronounced during systole; these recirculation environments diminish as flow accelerates towards peak flow at diastole. However, the size of these recirculation environments is very sensitive to the characteristics of each individual pulsatile waveform, particularly during systolic phase. These fundamental CFD studies will shed light on future patient monitor strategies, and enhance patients’ outcomes with individualised medications. |
Tuesday, November 20, 2018 2:21PM - 2:34PM |
Q17.00008: Effect of Wall Elasticity on Endothelial Shear Stress Calculations in Coronary Arteries Parastou Eslami, Alison L Marsden, Justin S Tran, Janet Lo, Ahmet Coskun, Peter Stone, Udo Hoffmann, Michael Lu Endothelial shear stress (ESS) regulates the coronary artery wall’s crucial functions to resist injury, suppress inflammation, and prevent atherosclerosis. Progression of coronary atherosclerosis is closely linked to vessel anatomy and location, often occurring at the outer edges of vessel bifurcations. In these areas, disturbed laminar flow patterns result in low ESS. Previous studies based on invasive imaging modalities have shown association of low ESS with atherosclerosis progression, however these studies were limited to visualization of a single branch at a time with rigid walls. Similar to other arteries in the body, coronary arteries have elastic walls that may affect the calculation of flow-driven ESS. Therefore, in this study, we use patient-specific computational fluid dynamics models based on computed tomography angiography images of the full 3D coronary tree to determine the effect of wall elasticity on calculated ESS. Using fluid-structure interaction modeling for elastic wall models, we found no substantial difference in time-averaged ESS (TAESS) calculated using rigid versus elastic walls. In addition, we compare TAESS at internal and external curvature and examine the effect of arterial curvature on the calculation of ESS. |
Tuesday, November 20, 2018 2:34PM - 2:47PM |
Q17.00009: Mechano-genetics of the cardiac development in embryonic medaka Sreyashi Chakraborty, Elizabeth Allmon, Marisol Sepulveda, Pavlos Vlachos Cardiovascular morphogenesis during embryonic development is influenced by the interplay between mechanical forces sensed by endothelial cells and the subsequent genetic response. A perturbation to this mechano-genetic interplay would lead to cardiovascular malformations. To investigate the hemodynamic cues that lead to altered gene expressions, we conduct a qPCR analysis on synthesized cDNA from medaka embryos starting at 12 hours post fertilization (hpf) to 12 days post fertilization (dpf). Five genes (FGF8, BMP4, NKX2.5, SMYD1 and HOX6b6) that contribute to early cardiac development were investigated. Concomitantly, the embryonic heart was imaged under a microscope from 3 dpf (after onset of circulation) to 14 dpf. PIV analysis was conducted on the images to calculate the velocity fields in the heart by cross-correlating red blood cell patterns. Hemodynamic metrics like flow velocity magnitude, pressure drop across ventricle, wall shear stress and cardiac wall strain were quantified and correlated to the gene expression in each dpf. This integrated mechano-genetic framework will further enhance knowledge about the developmental biology of the species. |
Tuesday, November 20, 2018 2:47PM - 3:00PM |
Q17.00010: Tiny hearts in big trouble: cardiac flow hydrodynamics in fetal single ventricle hearts Brett Meyers, R. Mark Payne, Pavlos Vlachos The fetal circulatory system is flexible and rapidly adaptive, undergoing extreme remodeling over the second and third trimesters. In order to monitor circulatory development, clinicians rely on fetal echocardiogram exams. However, exams focus mainly on tissue morphology, employing Doppler scans to look for other abnormalities such as valve disease and atrio-ventricular shunting. The study of human fetal cardiac hemodynamics has recently begun as advances in echocardiography improve spatial and temporal resolution. Still, more complex flow measurements such as vortex formation and intraventricular pressure remain relatively unexplored. This work focuses on human fetal cardiac flow measurements derived from normal and abnormal fetal echocardiogram exams from 20 weeks to 35 weeks (near term) using an in-house 2D color Doppler reconstruction method. We will explore how filling mechanics and flow structure change over the course of gestation and begin to understand how these are altered in the presence of abnormal circulatory systems. |
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