Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session ZC09: Biofluids: Large Vessels and Arteries III |
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Chair: Debanjan Mukherjee, University of Colorado Boulder Room: 140A |
Tuesday, November 21, 2023 12:50PM - 1:03PM |
ZC09.00001: Conformation of vWF in Converging/Diverging Channel Dennis Oztekin, Mustafa Usta, Cyrus K Aidun Undesired thrombus formation in arteries poses a significant challenge in managing cardiovascular diseases. The biomechanical behavior of von Willebrand Factor (vWF), a crucial protein involved in hemostasis, plays a critical role in mediating platelet adhesion and aggregation under flow conditions, thereby contributing to the pathological thrombus formation in arterial vessels. In this study, we employ numerical simulations to study the conformation of vWF as it passes through a converging/diverging pipe. The peak shear rates in the straight section upstream of the converging /diverging segment of the pipe are set well below the critical shear rate of the vWF being studied. Conversely, in the throat of the converging/diverging section wall shear rates are well above the critical shear rate. By simulating these flow conditions, we observe how vWF reacts to short bursts of high shear, analyzing cases where vWF extends and doesn’t extend in response to these shear bursts. Subsequently, we identify the conformations that more readily respond to shear. Understanding the complex interplay between vWF and its biomechanical properties in pathologically relevant geometries is crucial for elucidating thrombotic mechanisms and developing targeted interventions. |
Tuesday, November 21, 2023 1:03PM - 1:16PM |
ZC09.00002: In-vitro experimental investigation of the global hemodynamic effects of aortic coarctation on carotid and renal pulsatile blood flow Deniz Rafiei, Niema M Pahlevan Aortic coarctation is the congenital constriction of the aorta, mainly affecting the proximal descending part of it. This condition significantly impacts the local pulsatile hemodynamics in the aorta. If left untreated, the mortality rate can reach 90% by the time individuals reach 50 years of age. However, the global effects of this condition on other organs, such as the brain and kidneys, are not fully understood. Clinical studies have shown that coarctation acts as a reflection site that affects pulsatile energy transmission and the volume blood flow to the brain and kidneys. However, the extent of this potentially harmful excessive pulsatile energy caused by coarctation toward these organs is not thoroughly studied. In this study, we use a physiologically accurate in-vitro experimental setup that simulates the hemodynamics of the coupled atrioventricular-aortic system. Hemodynamic measurements are performed for various cardiac outputs, heart rates, aortic compliances, and coarctation degrees. Pulsatile energy transmission, wave intensity, and power spectrum analysis are evaluated for the brain and kidneys to investigate the underlying physics of arterial waves in coarctation cases. This study reports the effects of the aforementioned parameters on cerebral and renal hemodynamics, providing a better understanding of the pulsatile hemodynamic changes in aortic coarctation patients. The outcome of this study can help design new patient-specific therapeutic approaches. |
Tuesday, November 21, 2023 1:16PM - 1:29PM |
ZC09.00003: On the relationship between local hemodynamics and wall changes in cerebral aneurysms- A rare case with complete vascular tissue and lumen geometry Mehdi Ramezanpour, Yasutaka Tobe, Patrick Tatlonghari, Julia K Kofler, Juan R Cebral, Anne M Robertson Intracranial aneurysms represent a significant medical challenge due to their potential for sudden rupture and consequent severe physical disabilities. Deciding on treatment – high-risk surgery or leaving them untreated - is a complex dilemma that stems from the absence of reliable rupture risk assessments. Accurate risk assessment requires conjoined studies of mechanics and wall biology to unveil precise failure mechanisms. However, the challenge lies in the infeasibility of capturing tissues' microstructures in vivo. Here we have a rare case with premortem clinical CTA images and postmortem dissected tissue from an entire aneurysm and neighboring vasculature. We implement a framework for generating a high-fidelity computational model and perform in silico simulation to identify how intramural wall structure is correlated with heterogeneous aneurysm flow and wall stress. In-vivo CT images were used to create the vasculature model for blood flow simulations, and post-mortem micro-CT and multiphoton images of the vascular wall were employed to create the 3D wall model, its lipid pool, collagen, and elastin matrices. The presented framework enables efficient implementation of these scarce invaluable data sources to understand how flow patterns impact wall integrity and strength. |
Tuesday, November 21, 2023 1:29PM - 1:42PM |
ZC09.00004: Embolus Transport and Distribution in the Brain in the Presence of Contralateral Carotid Occlusion Ricardo T Roopnarinesingh, Michelle Leppert, Neel Jani, Debanjan Mukherjee Embolic Stroke of Undetermined Source comprises a significant amount of all ischemic strokes with the current ability to identify etiology being limited. Identifying stroke etiology is a vital factor in treatment efficacy and reducing recurrent events. The carotid arteries provide a critical location where bilateral buildup of atherosclerotic plaque can embolize and move into the cerebral arteries. Diseased carotids are suspect to Contralateral Carotid Occlusion (CCO) where one carotid artery is fully occluded and the other is partially occluded. The common understanding of carotid embolization is that stroke events are mainly limited to the ipsilateral hemisphere respective to the carotid artery. Contralateral transport can lead to possible confusion on the proper etiology from which a stroke originated thus leading to a decrease in treatment efficacy. We investigate how non-intuitive embolus transport from carotid and cardiogenic sources may occur in the presence of CCO. Using an in silico methodology, we developed a patient-specific hemodynamics and embolus transport model within the heart-to-brain pathway to conduct an investigation on how cardiogenic and carotid sourced embolization may complete non-intuitive embolus distribution in the form of contralateral movement. |
Tuesday, November 21, 2023 1:42PM - 1:55PM |
ZC09.00005: Data-Driven Modeling of Pressure Differentials over Vascular Junctions Natalia L Rubio, Luca Pegolotti, Martin R Pfaller, Jonathan Pham, Eric F Darve, Alison L Marsden Cardiovascular flow simulations provide valuable insight for surgical planning, but the high computational cost of traditional finite element modeling limits their use in clinical settings. Reduced-order models make simplifying assumptions that decrease computational cost, but also reduce their accuracy. We consider a zero-dimensional (0D) model in which a vasculature is modeled as an electric circuit, and pressure and flow are modeled as voltage and current respectively. The 0D model usually assumes constant pressure (static or dynamic) over vascular junctions, but this does not capture the complex, geometry-dependent flow effects in a junction, and is often a significant source of error. We propose a data-driven approach to predict the pressure drop over a vascular junction so that it can be accounted for in a 0D model. In particular, we represent the junction dynamics in the context of the electric circuit using a linear resistor, quadratic resistor, and inductor. The resistance/inductance of these elements is determined using data-fitting techniques trained on data from three-dimensional finite element simulations of flows in a cohort of synthetic junction geometries. We study the accuracy of our formulation using different regression techniques and compare it against the Unified0D+ model previously proposed by Mynard et al. |
Tuesday, November 21, 2023 1:55PM - 2:08PM |
ZC09.00006: Effect of the carotid geometry on the onset of atherosclerotic plaques Maria Vittoria V Salvetti, Jaskaran Singh, Alessio Innocenti, Katia Capellini, Alessandro Mariotti, Simona Celi Atherosclerosis is an inflammatory cardiovascular disease that leads to a gradual narrowing of blood vessels due to the formation of plaques inside the artery. The plaques result from the accumulation of lipidic substances over the years and could obstruct the blood flow to downstream vessels and organs. We aim to predict through Computational Fluid Dynamics (CFD) simulations the possible onset of carotid plaques and to analyze the influence of hemodynamic and geometric parameters on the early stages of the disease. |
Tuesday, November 21, 2023 2:08PM - 2:21PM |
ZC09.00007: AI-augmented hemodynamics: 3D blood flow field construction from pressure measurements Siva Viknesh, Ethan Sheomaker, Amirhossein Arzani Pressure is frequently measured clinically in coronary artery stenosis using invasive techniques such as fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR). We present a deep learning approach using physics-informed neural networks (PINN) to construct a 3D blood flow velocity field from pressure data along the centerline of an artery based on iFR measurements. First, we utilize the PINN framework with recent advancements, such as neuron-wise adaptive activation functions, for solving complex 3D flow fields in stenosed arteries. Then, we highlight the causality issue of the PINN framework over a spatial domain, and a methodology is proposed to resolve the issue. Using the proposed method, one calculates the unknown inlet and outlet boundary conditions and, subsequently, the entire flow field based on the pressure measurements. We apply our framework to a patient-specific coronary artery stenosis model and quantify its accuracy. Our AI-augmented approach enables one to obtain full blood flow field data based on experimental pressure wire measurement approaches. |
Tuesday, November 21, 2023 2:21PM - 2:34PM |
ZC09.00008: Poiseuille flow of an active gel in a cylindrical tube Thomas R Powers, Aparna Baskaran, Wan Luo, Robert A Pelcovits We consider a two-dimensional active nematic liquid crystal between two concentric circular boundaries. The anchoring conditions are hybrid, meaning that the nematic directors make different constant angles with the inner and outer boundaries. When the activity is zero, the system takes on the "magic spiral" geometry which was proposed by Robert Meyer to elucidate the balance of torques in nematic liquid crystals in equilibrium. When the activity is nonzero and the inner circle bounds a disk which is free to rotate, active flows spin the disk at a speed that depends on the activity, viscosity, liquid crystal parameters, and the size of the gap between the two circles. We calculate the rotation speed analytically using the frozen nematic approximation in which the effect of the flow on the nematic is disregarded, but the viscous flow is accounted for. We examine the accuracy of this approximation by numerically solving the full hydrodynamic equations. |
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