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 G19: Biological fluid dynamics: Hearts and Lungs |
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Chair: Kenneth Kiger, University of Maryland, College Park Room: Georgia World Congress Center B306 |
Monday, November 19, 2018 10:35AM - 10:48AM |
G19.00001: Forced motion of a cylinder within a liquid-filled elastic tube with application to minimally invasive medical procedures Amit Vurgaft, Shai B Elbaz, Amir D Gat We analyze the forced motion of an internal concentric rigid cylinder within an elastic liquid-filled tube. This configuration is relevant to various minimally invasive medical procedures in which solid devices are inserted into fluid-filled biological vessels (such as percutaneous revascularization, interventional radiology, endoscopies and catheterization). Insertion of the cylinder at a constant force is shown to involve three distinct regimes and time-scales: (i) initial shear dominant regime, (ii) increased fluidic pressure and a propagating peeling front regime, (iii) quasi-steady flow regime. A uniform solution for all regimes is presented. In the opposite case of extraction of the cylinder from the tube, the negative gauge pressure reduces the gap between the cylinder and the tube till a radial contact of the two solids. Asymptotic and numeric solutions are presented for the dynamics of the near-contact and full contact limits. We find that the cylinder exits the tube in a finite time for sufficiently small or large forces, while for an intermediate range of forces the radial contact creates a locking of the cylinder inside the tube. |
Monday, November 19, 2018 10:48AM - 11:01AM |
G19.00002: Tracking of virtual particles from volumetric velocity measurements: applications to physiological flows Omid Amili, Sean Moen, Robroy MacIver, Jafar Golzarian, Filippo Coletti Continuous advancements in medical imaging are allowing the study of physiological flows with increasing accuracy and resolution, both in vitro and in vivo. In several biomedical settings, the transport of particles is an important aspect of the fluid dynamic problem, for example in the delivery of inhaled or injected drugs, and the fate of harmful agents through vessels and airways where such particles have often significant inertia. Here we utilize volumetric (three-dimensional, three-component) velocity fields obtained by Magnetic Resonance Velocimetry (MRV) to study the transport of inertial particles in cardiovascular and respiratory flows. We apply a well-established form of the particle equation of motion to track particles of given inertia that are virtually released in the flow which allows to calculate Lagrangian trajectories. The method is applied to a range of cases, including: blood clots from left ventricle assist device, thrombi in brain aneurysms, embolizing particles for tumor targeting, and inhaled aerosols in the bronchial tree. |
Monday, November 19, 2018 11:01AM - 11:14AM |
G19.00003: Filtering flow measurements in the left ventricle using modal analysis Sarah Frank, Siavash Ameli, Andrew John Szeri, Shawn C Shadden Several studies have linked blood flow inside the heart to disease etiology. However, imaging intra-cardiac blood flow remains challenging, limiting our understanding of heart failure and its hemodynamic consequences. Phase-contrast MRI (PC-MRI) is the only non-invasive method that provides velocity information that is 3D, on a 3D grid. However, these fields are noisy and not divergence-free. Color-Doppler ultrasound is inexpensive and readily available, but only provides velocity information in a single direction. We have developed a modal analysis method to de-noise flow data in a 3D domain, producing a divergence-free flow field. The modes are calculated by minimizing the velocity gradient while enforcing a divergence-free condition across the domain. This enables measured velocity fields to be projected onto these modes using a least squares algorithm. The method is tested on the results of a computational fluid dynamics simulation with artificial noise added to the velocity field and on PC-MRI data. Different boundary conditions, mesh sizes, and numbers of modes are tested. The method is also tested as a reconstruction method for 3D color-Doppler ultrasound data by using the CFD and PC-MRI data to construct virtual ultrasound data sets. |
Monday, November 19, 2018 11:14AM - 11:27AM |
G19.00004: Wall-Bounded Vorticity in the Right Heart from 4DMRI Measurements Jean Hertzberg, Joel Human, Alejandro Perez, Reece Jones, James Browning, Joyce Schroeder, Brett Fenster Time-resolved 3D cardiac magnetic resonance phase contrast flow imaging (4DMRI) was used to measure blood flow in the human heart in a small cohort of normal subjects and patients with pulmonary hypertension (PH). The ultimate goal of this work is to determine appropriate metrics to track the progress of diseases such as PH. Vorticity was derived from these measurements and decomposed into streamwise and helical components, with attention focused on the right ventricle and right atrium. The interaction of vorticity and structures such as valve leaflets, papillary muscles and chordae tendineae will be discussed. |
Monday, November 19, 2018 11:27AM - 11:40AM |
G19.00005: Optimal vortex formation time is not attained in the heart: In vivo analysis by dynamic 3D enstrophy mapping from 4D Flow MRI Mohammed S.M. Elbaz, Trung Bao Le, Pankaj Garg, Arno Roest, Boudewijn P.F. Lelieveldt, Sven Plein, Jos J.M. Westenberg, Rob J. van der Geest, Fotis Sotiropoulos We use dynamic 3D velocity field from in vivo 4D Flow MRI to revisit the optimal vortex formation time (OVFT) hypothesis in human left ventricle during diastole as opposed to the previous 2D-based derivation. In total, 34 healthy volunteers (20-68 years) underwent in-vivo 4D Flow MRI. Dynamic 3D LV geometry was segmented over E-filing (~12 time-points). 3D voxel-wise enstrophy maps were computed over the LV. We then constructed a profile of the instantaneous total volumetric enstrophy (Ei) evolution relative to the vortex formation time (Ti). Despite the wide age range of the studied population, 4D Flow MRI-based volumetric results showed that in all studied healthy subjects Ei never attains its asymptotic maximum at the “optimal” time (Ti~4). Instead, Ei consistently presented a decay phase at around Ti=1.23±0.25, stimulated by the inflow interaction with the confining dynamic LV geometry. Our results indicate that the OVFT hypothesis is not applicable in vivo in the healthy LVs studied due to the revealed decay phase that has not been reported in previous 2D derivations. Thus, our results warrant the need for studies revising/extending the previously hypothesized binary classification (optimal or non-optimal vortex formation) for assessing diastolic (dys)function in vivo. |
Monday, November 19, 2018 11:40AM - 11:53AM |
G19.00006: Simulation of Left Ventricular Hemodynamics from 4D-Flow MRI Data Trung Bao Le, Mohammed Elbaz, Rob Van deer Geest, Fotis Sotiropoulos We investigate the diastolic hemodynamics in a patient-specific left ventricle (LV) of a healthy subject using four dimensional flow magnetic resonance imaging (4D-Flow MRI) measurement and numerical simulation. From four dimensional Cardiac Magnetic Resonance (CMR) Imaging data, the kinematics of the endocardium is reconstructed. The endocardial kinematics and the time varying velocity distribution from 4D-Flow MRI at the mitral orifice are prescribed as boundary conditions for the numerical simulation. Both 4D-Flow MRI data and numerical results show the classical formation of the mitral vortex ring (MVR) during E-wave filling. The in-vivo data reveals that a large three-dimensional vortex structure forms near in the mid-level region of LV during diastasis (mid-level vortex). This mid-level vortex is formed simultaneously with the MVR and has not been reported in the literature. Our results suggest that numerical simulation can be used to provide useful hemodynamic data given the inputs from 4D-Flow MRI, which is now available in clinical practice. |
Monday, November 19, 2018 11:53AM - 12:06PM |
G19.00007: Towards personalized cardiology for coarctation: computational-mechanics and imaged-based diagnostic frameworks Zahra Keshavarz-Motamed Coarctation of the aorta (COA) is an obstruction of the aorta distal to the left subclavian artery with different hemodynamic severity and clinical manifestations, varying from mild COA to severe narrowing while accompanied by other cardiovascular diseases. Despite advancements in interventions, life expectancy for COA patients remains low due to morbidity. The sources of morbidity can be explained on the basis of adverse hemodynamics: abnormal flow patterns and bio-mechanical forces, often categorized by disturbed and turbulent flow, and in some cases by an increase in the heart workload, leading to the development and progression of disease. Therefore, flow quantification can be greatly useful for accurate and early diagnosis. In this work, a computational-mechanics and imaging-based framework was developed that functions as a diagnostic method for COA. It quantifies 3-D local fluid dynamics and global hemodynamics (heart workload) non-invasively in COA patients based on patient-specific hemodynamic input parameters. The framework was validated against pre and post-intervention clinical data (cardiac catheterization and Doppler echocardiography) in 25 patients. |
Monday, November 19, 2018 12:06PM - 12:19PM |
G19.00008: Synchrotron microtomography of coiled aneurysm phantoms: improving accuracy of porous medium models for coil embolization of intracranial aneurysms Michael C. Barbour, Fanette Chassagne, Laurel Marsh, Venkat Keshav Chivukula, Christian Geindreau, Sabine Rolland du Roscoat, Cory M. Kelly, Samuel Levy, Micheal R. Levitt, Louis J. Kim, Alberto Aliseda Cerebral aneurysms are often embolized with coils to reduce blood flow into the aneurysmal sac, promoting the development of a thrombus to reduce the risk of rupture. Computational analysis of the hemodynamics inside the aneurysm, before and after treatment, is a useful tool to better understand the effect of endovascular treatment on thrombus formation. The current standard is to model the coil mass as an isotropic homogeneous porous medium. This study proposes a new anisotropic porous model created by homogenization of the exact coil geometry obtained from Synchrotron X-ray Microtomography. Silicon phantoms built from patient-specific aneurysms were treated with embolic coils and microtomography of these models was performed at ESRF (Grenoble, France). The coil geometries were integrated with the vessel lumen reconstruction for CFD analysis. The results of standard homogeneous isotropic and novel heterogeneous anisotropic models are compared to the flow simulations around the actual coil geometries. The homogenization-based coil model was found to be more accurate (closer to the coil-resolved simulations) for the prediction of flow in the aneurysmal sac (+70% improvement in RSME compared to isotropic porous media) and wall shear stress at the neck of the aneurysm (+64%). |
Monday, November 19, 2018 12:19PM - 12:32PM |
G19.00009: Time resolved 3D flow measurements in idealized and realistic upper airway models under high frequency ventilation Sahar Jalal, Eliram Nof, Josue Sznitman, Filippo Coletti When the inhalation and exhalation phase alternate rapidly, respiratory flows are fundamentally different from steady conditions. This is particularly relevant for high frequency ventilation (HFV), a technique of mechanical ventilatory support routinely employed to treat acute lung injury and respiratory distress syndrome, which uses higher-than-normal airflow oscillation frequencies coupled with low tidal volumes. Here, we experimentally investigate the three-dimensional structure of respiratory flows for Reynolds and Womersley numbers relevant to HFV. We first focus on an idealized airway model which mimics the self-similar branching of the human bronchial tree. Volumetric velocity fields are acquired via Magnetic Resonance Velocimetry (MRV) and Tomographic Particle Image Velocimetry (Tomo-PIV). These are compared with measurements obtained, under identical regimes, in a 3D morphometrically-faithful airway model to assess the impact of true bronchial anatomy on airflow features. In both idealized and realistic cases, the simultaneous presence of inspiratory and expiratory air motions highlights the importance of transport mechanisms specific to HFV. |
Monday, November 19, 2018 12:32PM - 12:45PM |
G19.00010: Circulation of micro-particles in stenosed microvessels: nanoworm outperforms sphere Huilin Ye, Zhiqiang Shen, Ying Li We explore the circulation of micro-particles (MPs) in stenosed microvessels with different constriction ratios and lengths through three-dimensional fluid-structure interaction simulations. The blood flow dynamics is solved by Lattice Boltzmann method (LBM). We employ coarse-grained model to capture the dynamics of red blood cells (RBCs) and MPs. And the LBM and coarse-grained model are coupled by immersed boundary method. We find that high constriction ratio enhances the accumulation of spherical particles in the front of the constriction, while lowers the margination of spherical particles after the constriction. This effect becomes more significant for the microvessels with longer constriction length. However, nanoworms demonstrate different distributions along the flow and in the axial directions. Comparing with spherical MPs, nanoworms distribute more uniformly without obvious accumulation in front of the constriction region along the flow. In the axial direction, nanoworms show stronger concentration in the center of the flow. It is attributed to the deformability that nanoworms can deform under the shear flow and migrate to the center of blood stream. |
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