Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q29: Biological Fluids Dynamics: Large Vessels |
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Chair: Fanette Chassagne, University of Washington Room: 611 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q29.00001: Hemodynamics Assessments of Ascending Thoracic Aortic Aneurysm -- the Influence of Hematocrit with Fluid-Structure Interaction Analysis Han Hung Yeh, Simon Rabkin, Dana Grecov An aortic aneurysm is one of the cardiovascular diseases with localized abnormal growth of a blood vessel risking rupture or dissect. The precise pathological pathway for aneurysm progression and formation is not completely understood. In the current study, ascending thoracic aortic aneurysms (ATAA) are investigated using a fully coupled fluid-structure interaction method focusing on the changes in hematocrit under normotension and hypertension. Blood was modeled as a laminar incompressible flow using the Quemada model with varying hematocrits. The arterial wall anisotropy and hyperelasticity were considered. Given the influence of hematocrits on the degree of shear-thinning of blood, the current result could provide valuable information in clinical practice. Our results suggested that with the increase in hematocrit, the shear stress distribution and the maximum shear stress magnitude along the arterial wall would increase significantly. The wall stress distributions, however, remained unchanged with respect to the changes in hematocrit. In addition, the distribution of von Mises stress indicated that elevated stress under hypertension could depend on geometry. This geometrical influence in ATAA could be a risk factor predicting further aortic expansion. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q29.00002: The hidden role of wall shear stress in fluid mechanics of coronary artery atherosclerosis Amirhossein Arzani, Mostafa Mahmoudi Wall shear stress (WSS) is arguably the most important parameter in the biomechanics of atherosclerosis. Traditionally, WSS is used to quantify the frictional force on the endothelial cells and study mechanotransduction. However, WSS also provides valuable information about near-wall transport. Biologically, near-wall transport of certain biochemicals and cells influence atherosclerosis progression. The recent concept of Langrangian WSS structures (WSS manifolds) provides a connection between WSS vectors and near-wall transport. In this talk, we demonstrate the connection between WSS and near-wall localization of several atherogenic and atheroprotective biochemicals and cells in coronary artery atherosclerosis. Finally, an automated computational framework developed in FEniCS is presented to study the two-way coupling between WSS and plaque growth in coronary arteries. A phenomenological WSS driven growth model is developed to simulate plaque growth, which in turn influences the blood flow and WSS patterns. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q29.00003: Optimization of saline flushing of the coronary artery via two-lumen catheter for visualization of chronic total occlusions Syed Faisal, Eric Seibel, Alberto Aliseda A Chronic Total Occlusion (CTO) is caused by atherosclerotic plaque that occludes blood flow in a coronary artery. To improve treatment outcomes, visualization of the occlusion and surrounding coronary artery wall supports diagnosis and guides treatment. We investigate fluid interaction between blood and saline from different catheter designs, to understand the dynamics of blood displacement and low-Reynolds number mixing, and to optimize the catheter operating parameters involved in flushing of blood from the arterial lumen between the catheter tip and the CTO. The pressures develop during the flushing process and the time to obtain optical transparency in the lumen are measured. Suction is introduced to influence the flushing process. The incorporates changes to the artery size, as well as the arterial pulsatile blood flow, along with changes in the relative position of the fluid injection and suction lumens. The plaque morphology is varied to mimic its build up in arteries, testing the viability of the catheter uses under a wide range of physiological and anatomical conditions. A novel method of saline injection, suction and control, which helps reduce risk of the catheter failure and avoids injury to the patient, is developed. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q29.00004: Quantifying pumping effort and peristaltic work using balloon dilation catheters. Shashank Acharya, Wenjun Kou, Sourav Halder, John E. Pandolfino, Peter J. Kahrilas, Neelesh A. Patankar Balloon catheters are widely used to study the mechanical response of blood vessels as well as the active and passive response of tubular organs like the esophagus. In this work, we focus on the EndoFLIP, a device used to characterize the esophagus' response to dilation. We present a simplified 1D model to predict the system's response to peristalsis and then use it to generate work curves that show how the muscle energy is being spent. We also observe the development of different pumping regimes based on the operating parameters and present work curves for each of these patterns. An extension of this 1D model is used to enhance data obtained from the device and generate work curves for patients with abnormal peristalsis. The detailed characterization of this system presented here will aid in better interpreting the data obtained from balloon dilation catheters used in patients for any tubular organs or tissue vessels. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q29.00005: Spatiotemporal characterization of pulmonary hypertension under pulsatile flow conditions Narasimha Rao Pillalamarri, Senol Piskin, Ender Finol Pulmonary hypertension (PH) is a progressive disease characterized by elevated pressure and vascular resistance in pulmonary arteries. Nearly one quarter of a million hospitalizations occur annually in the U.S. with PH as the primary or secondary condition. A definitive diagnosis of PH requires right heart catheterization (RHC) in addition to a chest computed tomography, a walking test, and others. RHC is invasive has inherent risks and contraindications. This study aims to investigate non-invasive surrogates for RHC measures. Pulsatile hemodynamic simulations were conducted in 28 PH patient-specific geometries with a flow solver developed by customizing OpenFOAM libraries (v5.0, The OpenFOAM Foundation). Quasi patient-specific boundary conditions were implemented using a Womersley inlet velocity profile and resistance outflow conditions. Hemodynamic indices such as wall shear stress (WSS), time-averaged WSS, oscillatory shear index, and blood damage index were evaluated along with clinical metrics such as pulmonary vascular resistance and compliance to assess possible spatiotemporal correlations. The results are promising in the context of a long-term goal of identifying computational biomarkers that can serve as surrogates for invasive diagnostic protocols of PH. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q29.00006: Acoustic trapping and collapsing of microbubbles in stents. Feiyan Cai, Fei Li, Pengfei Zhang, Hairong Zheng Stents are commonly used in a coronary artery or any artery after angioplasty, but has the drawback to cause arterial restenosis. Targeted drug delivery has proved their efficacy at preventing coronary restenosis near stents. Here we propose a microbubble-based approach to enhance drug delivery by ultrasonically exciting the elastic resonances of the stents to generate a sound field that can trap and collapse microbubbles carrying drugs, which are consequently released near the stents. We report numerical and experimental results displaying the procedure of acoustic trapping and collapsing of microbubbles near the resonant polylactide (PLA) stents. Ultrasound of 1.5MHz is used to drive the stent resonances and generate a localized sound field that attracts microbubbles from the vessel center to the stent walls. These trapped microbubbles collapse near the surface of the stents when the input power of ultrasound is suddenly increased. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q29.00007: Coronary Stenosis Diagnosing System Using 2-step Machine Learning Algorithm Young Woo Kim, Susie Ryu, Heemin Lee, Joon Sang Lee In this study, a two-step machine learning (ML) algorithm is introduced to estimate fractional flow reserve (FFR) along with decision (DEC) for coronary artery. This paper suggests the possibility of ML-based FFR to overcome the computational fluid dynamics (CFD) based FFR estimation, which includes calculation time and accuracy. Both synthetic model and patient model are used for the training of 2-step algorithm. In the first step, synthethic models are analyzed by CFD method and are used to train Gaussian progress regression model in order to increase the quantity of data. In this process, not only FFR but also flow characteristics are considered. Patient models are used to train the second step of the algorithm, which is based on a support vector machine. This step provides more information related to biometrical features from the patient. In result, both the calculation time and accuracy of the model were higher for ML-based FFR than that from CFD-based FFR. This study suggests that both flow characteristics and biometrical features should be also included in the dataset of ML algorithm, by analyzing the weight factor of each features. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q29.00008: Quantifying the Energy Loss in Aortic Stenosis through Fluid-Structure Interaction Rana Zakerzadeh Supravalvular aortic stenosis is a defect accompanied by a narrowing of the ascending aorta and the stenosed area is subjected to abnormal hemodynamics and pressure drop. The pressure gradient across the stenosed region indicates the energy loss of the blood flow and is indicative of the extra work for the muscle of the left ventricle. The goal of this work is to develop a novel modeling approach to determine the accurate prediction of the pressure drop across the stenotic. We develop a computational method to simulate the propagation of pressure waves and the related arterial wall deformation. Blood is modeled using Navier-Stokes equations and the arterial wall consists of a thick material which accounts for the media and adventitia. Model simulations of the aortic blood flow under physiological conditions were performed using finite element method. The energy estimation is derived from weak formulation and applied to the stenosed artery to assess energy loss. The numerical simulations investigate the relation between the flow condition, pressure gradient and wall deformation for different levels of stenosis to cover the broad range in the degree of narrowing, ranging from trivial to severe. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q29.00009: Reduced order modeling of pulsatile blood flow: multistage dynamic mode decomposition with control Milad Habibi, Scott Dawson, Amirhossein Arzani Dynamic mode decomposition (DMD) has emerged in recent years as a purely data-driven technique to reduce snapshots of data to a best-fit linear reduced order model. Direct application of DMD to pulsatile cardiovascular flows is challenging. First, the unsteady nature of the input blood flow rate needs to be accounted for. Second, the flow topology can vary noticeably in different phases of the cardiac cycle. To overcome these challenges, we propose a new multistage dynamic mode decomposition with control (mDMDc) technique. The heart is considered as a controller, and the pulsatile inlet flow rate is the input to our system. Blood flow data are divided between different phases of the cardiac cycle and DMD with control is applied to each phase. We apply mDMDc to patient-specific computational fluid dynamics data (velocity and wall shear stress vectors) in cerebral aneurysm and coronary artery stenosis models. Reconstruction errors are presented and different modes are compared between velocity and wall shear stress. [Preview Abstract] |
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