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 R24: Biofluids: Cardiovascular Disease III |
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Chair: Lorenzo Rossini, UC San Diego Room: 302 |
Tuesday, November 24, 2015 12:50PM - 1:03PM |
R24.00001: Clinical Assessment of Intraventricular Blood Transport in Patients Undergoing Cardiac Resynchronization Therapy Lorenzo Rossini, P. Martinez-Legazpi, Y. Benito, C. Perez del Villar, A. Gonzalez-Mansilla, A. Barrio, R. Yotti, A.M. Kahn, S.C. Shadden, F. Fernandez-Aviles, J. Bermejo, J.C. del Alamo In the healthy heart, left ventricular (LV) filling generates flow patterns which have been proposed to optimize blood transport by coupling diastole and systole phases. We present a novel image-based method to assess how flow patterns influence LV blood transport in patients undergoing cardiac resynchronization therapy (CRT). Solving the advection equation with time-varying inflow boundary conditions allows to track the transport of blood entering the LV in the different filling waves, as well as the transport barriers which couple filling and ejection. The velocity fields were obtained using echocardiographic color Doppler velocimetry, which provides two-dimensional time-resolved flow maps in the apical long axis three-chamber view of the LV. We analyze flow transport in a group of patients with CRT devices as well as in healthy volunteers. In the patients under CRT, the device programming was varied to analyze flow transport under different values of the atrioventricular (AV) conduction delay and to model tachycardia. This analysis illustrates how CRT influences the transit of blood inside the LV, contributes to conserving kinetic energy and favors the generation of hemodynamic forces that accelerate blood in the direction of the LV outflow tract. [Preview Abstract] |
Tuesday, November 24, 2015 1:03PM - 1:16PM |
R24.00002: Optimization of the Outflow Graft Position and Angle in a Left Ventricular Assist Device Patrick McGah, Anthony Prisco, Jennifer Beckman, Nahush Mokadam, Claudius Mahr, Alberto Aliseda The placement of the outflow graft in the aorta plays a key role in the hemodynamics of Left Ventricle Assist Devices (LVAD), a medical device with a growing importance in the treatment of end-stage heart failure. We use a patient-specific computational model of the VAD and the ascending aorta to investigate the impact of VAD outflow graft configuration on the residence time and wall shear stresses along the ascending aorta and the ostia of the upper branches. The flow induced by the combination of VAD output through the graft anastomosed to the aorta and the limited cardiac output through intermittent opening of the aortic valve is studied to determine the nature of thrombogenic flow patterns. Outflow grafts are virtually anastomosed along the ascending aorta or subclavian artery of the patient-specific model at different positions and angles that are surgically-informed. Detailed markers of thrombosis, such as cell residence time, wall shear stress, and shear stress gradients are analyzed and compared for the different configurations. The angle of incidence of the outflow graft critically influences the volume of recirculating flow between aortic valve and anastomosis, and the aortic pressure acting against aortic valve opening. [Preview Abstract] |
Tuesday, November 24, 2015 1:16PM - 1:29PM |
R24.00003: Wall shear stress indicators in abnormal aortic geometries Lisa Prahl Wittberg, Stevin van Wyk, Laszlo Fuchs, Ephraim Gutmark, Iris Gutmark-Little Cardiovascular disease, such as atherosclerosis, occurs at specific locations in the arterial tree. Characterizing flow and forces at these locations is crucial to understanding the genesis of disease. Measures such as time average wall shear stress, oscillatory shear index, relative residence time and temporal wall shear stress gradients have been shown to identify plaque prone regions. The present paper examines these indices in three aortic geometries obtained from patients whose aortas are deformed due to a genetic pathology and compared to one normal geometry. This patient group is known to be prone to aortic dissection and our study aims to identify early indicators that will enable timely intervention. Data obtained from cardiac magnetic resonance imaging is used to reconstruct the aortic arch. The local unsteady flow characteristics are calculated, fully resolving the flow field throughout the entire cardiac cycle. The Quemada model is applied to account for the non-Newtonian properties of blood, an empirical model valid for different red blood cell loading. The impact of the deformed aortic geometries is analyzed to identify flow patterns that could lead to arterial disease at certain locations. [Preview Abstract] |
Tuesday, November 24, 2015 1:29PM - 1:42PM |
R24.00004: The Generation and Propagation of Arterial Murmurs from a Stenosed Artery: A Computational Study Chi Zhu, Jung-Hee Seo, Hani Bakhshaee, Rajat Mittal Cardiac auscultation - the procedure of diagnosing cardiovascular conditions using the stethoscope - has been used effectively for over a hundred years but still, the flow mechanism(s) responsible for the generation of these murmurs, as well as the effect of intervening tissue on the propagation of these murmurs, is not well understood. In this study, a one-way coupled, hybrid approach is used to investigate the propagation of murmurs generated from the flow in a stenosed artery. Specifically, the flow in the modeled artery is solved by an incompressible Navier-Stokes solver with the immersed-boundary method. The structural wave propagation in the tissue is resolved by a high-order, linear viscoelastic wave solver, and a mathematical decomposition is applied to separate the compressional and shear component of the acoustic wave propagating through the tissue. The simulations suggest, somewhat counterintuitively, that the shear wave contributes a significant component to the signal picked up by a stethoscope, and that this component carries much of the information that characterizes the source of the murmur. The implications of this for cardiac auscultation and further modeling of hemoacoustics are discussed. The effect of the stenosis severity and the flow pulsatility will also be investigated. [Preview Abstract] |
Tuesday, November 24, 2015 1:42PM - 1:55PM |
R24.00005: A Computational Chemo-Fluidic Modeling for the Investigation of Patient-Specific Left Ventricle Thrombogenesis Rajat Mittal, Jung Hee Seo, Thura Abd, Richard T. George Patients recovering from myocardial infarction (MI) are considered at high-risk for cardioembolic stroke due to the formation of left ventricle thrombus (LVT). The formation of LVT is the result of a complex interplay between the fluid dynamics inside the ventricle and the chemistry of coagulation, and the role of LV flow pattern on the thrombogenesis was not well understood. The previous computational study performed with the model ventricles suggested that the local flow residence time is the key variable governing the accumulation of coagulation factors. In the present study, a coupled, chemo-fluidic computational modeling is applied to the patient-specific cases of infracted ventricles to investigate the interaction between the LV hemodynamics and thrombogensis. In collaboration with the Johns Hopkins hospital, patient-specific LV models are constructed using the multi-modality medical imaging data. Blood flow in the left ventricle is simulated by solving the incompressible Navier-Stokes equations and the biochemical reactions for the thrombus formation are modeled with convection-diffusion-reaction equations. The formation and deposition of key coagulation chemical factors are then correlated with the hemodynamic flow metrics to explore the biophysics underlying LVT risk. [Preview Abstract] |
Tuesday, November 24, 2015 1:55PM - 2:08PM |
R24.00006: Ansys Fluent versus Sim Vascular for 4-D patient-specific computational hemodynamics in renal arteries Avinash Mumbaraddi, Huidan (Whitney) Yu, Alan Sawchuk, Michael Dalsing The objective of this clinical-need driven research is to investigate the effect of renal artery stenosis (RAS) on the blood flow and wall shear stress in renal arteries through 4-D patient-specific computational hemodynamics (PSCH) and search for possible critical RASs that significantly alter the pressure gradient across the stenosis by manually varying the size of RAS from 50{\%} to 95{\%}. The identification of the critical RAS is important to understand the contribution of RAS to the overall renal resistance thus appropriate clinical therapy can be determined in order to reduce the hypertension. Clinical CT angiographic data together with Doppler Ultra sound images of an anonymous patient are used serving as the required inputs of the PSCH. To validate the PSCH, we use both Ansys Fluent and Sim Vascular and compare velocity, pressure, and wall-shear stress under identical conditions. [Preview Abstract] |
Tuesday, November 24, 2015 2:08PM - 2:21PM |
R24.00007: Numerical simulation of hemorrhage in human injury Kwitae Chong, Chenfanfu Jiang, Anand Santhanam, Peyman Benharash, Joseph Teran, Jeff Eldredge Smoothed Particle Hydrodynamics (SPH) is adapted to simulate hemorrhage in the injured human body. As a Lagrangian fluid simulation, SPH uses fluid particles as computational elements and thus mass conservation is trivially satisfied. In order to ensure anatomical fidelity, a three-dimensional reconstruction of a portion of the human body --here, demonstrated on the lower leg-- is sampled as skin, bone and internal tissue particles from the CT scan image of an actual patient. The injured geometry is then generated by simulation of ballistic projectiles passing through the anatomical model with the Material Point Method (MPM) and injured vessel segments are identified. From each such injured segment, SPH is used to simulate bleeding, with inflow boundary condition obtained from a coupled 1-d vascular tree model. Blood particles interact with impermeable bone and skin particles through the Navier-Stokes equations and with permeable internal tissue particles through the Brinkman equations. The SPH results are rendered in post-processing for improved visual fidelity. The overall simulation strategy is demonstrated on several injury scenarios in the lower leg. [Preview Abstract] |
Tuesday, November 24, 2015 2:21PM - 2:34PM |
R24.00008: A Computational Approach to Model Vascular Adaptation During Chronic Hemodialysis: Shape Optimization as a Substitute for Growth Modeling S. M. Javid Mahmoudzadeh Akherat, Michael Boghosian, Kevin Cassel, Mary Hammes End-stage-renal disease patients depend on successful long-term hemodialysis via vascular access, commonly facilitated via a Brachiocephalic Fistula (BCF). The primary cause of BCF failure is Cephalic Arch Stenosis (CAS). It is believed that low Wall Shear Stress (WSS) regions, which occur because of the high flow rates through the natural bend in the cephalic vein, create hemodynamic circumstances that trigger the onset and development of Intimal Hyperplasia (IH) and subsequent CAS. IH is hypothesized to be a natural effort to reshape the vessel, aiming to bring the WSS values back to a physiologically acceptable range. We seek to explore the correlation between regions of low WSS and subsequent IH and CAS in patient-specific geometries. By utilizing a shape optimization framework, a method is proposed to predict cardiovascular adaptation that could potentially be an alternative to vascular growth and remodeling. Based on an objective functional that seeks to alter the vessel shape in such a way as to readjust the WSS to be within the normal physiological range, CFD and shape optimization are then coupled to investigate whether the optimal shape evolution is correlated with actual patient-specific geometries thereafter. [Preview Abstract] |
Tuesday, November 24, 2015 2:34PM - 2:47PM |
R24.00009: Intraventricular filling under increasing left ventricular wall stiffness and heart rates Milad Samaee, Hong Kuan Lai, Joseph Schovanec, Arvind Santhanakrishnan, Sherif Nagueh Heart failure with normal ejection fraction (HFNEF) is a clinical syndrome that is prevalent in over 50{\%} of heart failure patients. HFNEF patients show increased left ventricle (LV) wall stiffness and clinical diagnosis is difficult using ejection fraction (EF) measurements. We hypothesized that filling vortex circulation strength would decrease with increasing LV stiffness irrespective of heart rate (HR). 2D PIV and hemodynamic measurements were acquired on LV physical models of varying wall stiffness under resting and exercise HRs. The LV models were comparatively tested in an in vitro flow circuit consisting of a two-element Windkessel model driven by a piston pump. The stiffer LV models were tested in comparison with the least stiff baseline model without changing pump amplitude, circuit compliance and resistance. Increasing stiffness at resting HR resulted in diminishing cardiac output without lowering EF below 50{\%} as in HFNEF. Increasing HR to 110 bpm in addition to stiffness resulted in lowering EF to less than 50{\%}. The circulation strength of the intraventricular filling vortex diminished with increasing stiffness and HR. The results suggest that filling vortex circulation strength could be potentially used as a surrogate measure of LV stiffness. [Preview Abstract] |
Tuesday, November 24, 2015 2:47PM - 3:00PM |
R24.00010: Measurements of flow structure interaction in a plaqued artificial artery using an index matched flow facility Akash Jain, Larry Brock, Jian Sheng The aim of the experiment is to study the flow structure interaction in an arterial model with a simulated plaque inside a closed loop index matched pulsatile flow facility. The test section is 24.5 inches long 6 inches wide. The experimental models are compliant polymer (PDMS) tubes having an outer diameter of 9 mm and a wall thickness of 1 mm. The plaque on the models are simulated by means of a radially asymmetric bump. Both flow and polymeric structures are doped with different particles and imaged with Particle Image Velocimetry (PIV) method. To minimize the optical distortion near liquid solid interface, the facility is fully index matched with NaI at 40{\%} by weight. A suite of analysis procedures quantifying complex interactions including solid-fluid phase separation, near wall flow analysis, and wall shear stress approximation as well as wall deformation quantification, have been developed and applied to study the healthy and plaqued artificial arteries in steady and pulsatile flow conditions. 3D ensemble velocity fields, wall shear stress distributions and corresponding strain deformations will be presented. [Preview Abstract] |
Tuesday, November 24, 2015 3:00PM - 3:13PM |
R24.00011: Right Heart 4DMRI Flow Visualization in Normal and Hypertensive subjects Jean Hertzberg, James Browning, Brett Fenster, Joyce Schroeder Recent advances in time-resolved 3D cardiac magnetic resonance imaging (4DMRI) have allowed for the 3-dimensional characterization of blood flow in the right ventricle (RV) and right atrium (RA). In this talk, an overview of a large, ongoing, multi-disciplinary investigation of 4D right heart hemodynamics in normal and pathologic patients is given, as well as lessons learned from 4DMRI cardiac research. Time-resolved visualization techniques for understanding and communicating complex right heart flow structures throughout the cardiac cycle are presented. Finally, a qualitative visual comparison of 3D flow structures in the vena cava, RA, and RV between healthy subjects and pulmonary hypertensive patients is presented. [Preview Abstract] |
Tuesday, November 24, 2015 3:13PM - 3:26PM |
R24.00012: Right Heart Vorticity and Right Ventricular Diastolic Dysfunction James Browning, Jean Hertzberg, Brett Fenster, Joyce Schroeder Recent advances in cardiac magnetic resonance imaging (CMR) have allowed for the 3-dimensional characterization of blood flow in the right ventricle (RV) and right atrium (RA). In this study, we investigate and quantify differences in the characteristics of coherent rotating flow structures (vortices) in the RA and RV between subjects with right ventricular diastolic dysfunction (RVDD) and normal controls. Fifteen RVDD subjects and 10 age-matched controls underwent same day 3D time resolved CMR and echocardiography. Echocardiography was used to determine RVDD stage as well as pulmonary artery systolic pressure (PASP). CMR data was used for RA and RV vortex quantification and visualization during early ventricular diastole and the results are compared between healthy subjects and those with RVDD. The resulting trends are discussed and hypotheses are presented regarding differences in vortex characteristics between healthy and RVDD subjects cohorts. [Preview Abstract] |
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