Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session A13: Biological Fluid Dynamics: Physiological I |
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Chair: Jiacheng Zhang, Purdue; Niema Pahlevan, University of Southern California Room: 141 |
Sunday, November 20, 2022 8:00AM - 8:13AM |
A13.00001: Wave pumping mechanism from aortic stretch and recoil in the systemic circulation Arian Aghilinejad, Haojie Geng, Niema M Pahlevan Understanding the hemodynamic interactions between the heart and the vasculature is the crucial step toward developing new diagnostic devices and therapeutic approaches. One such interaction is the physical connection between the proximal ascending aorta, aortic annulus, and the left ventricle (LV). Recent clinical studies have visualized aortic root motion due to the LV systolic long-axis shortening, wherein the aortic root is displaced downward during systole and returns passively to its previous position in diastole. While this displacement results in energy storage in aorta’s spring-like elements, it is unknown whether the stretch-related aortic dynamic mode can result in a wave pumping effect in the aorta, and hence offers the heart a supplementary pumping mechanism. This study is designed to understand the underlying wave pumping mechanism created by aortic stretching and recoil. To investigate this phenomenon, we employ an in-vitro hydraulic model that has hemodynamic properties similar to the human systemic circulation. A driving component is designed and employed to mimic the stretch-related aortic dynamic mode. |
Sunday, November 20, 2022 8:13AM - 8:26AM |
A13.00002: Longitudinal resonance wave pumping in compliant tubes: a bio-inspired approach Niema M Pahlevan, Bryson Rogers, Haojie Geng, Arian Aghilinejad Impedance pump is a valveless pump that operates based on the principles of wave propagations and reflections. In its simplest form, an impedance pump is composed of a fluid-filled elastic tube connected to rigid tubes (reflection sites) and a pincher (wave generator). Previous studies have shown that aorta acts as an impedance pump where waves are created by the left ventricle (LV) pulsatile flow. Longitudinal stretching of the ascending aorta during the contraction of the LV is an important determinant of the aortic biodynamics and recent clinical studies have shown that this mechanism aids in LV early filling. To the best of our knowledge, the association between stretch-related dynamic mode of the ascending aorta and its impact on aortic hemodynamics has not been studied. Inspired by this natural aortic mechanism, we conducted a comprehensive analysis of the longitudinal model of the impedance pump. In this type of the impedance pump, waves are created by longitudinal stretching of the elastic wall. Our results indicate that stretch-related wave propagation and reflection in a fluid-filled compliant tube can create a pumping mechanism. Like other impedance pumps, both the direction and the magnitude of the net flow depend on the wave dynamic characteristics. |
Sunday, November 20, 2022 8:26AM - 8:39AM |
A13.00003: Evaluating Intravascular Transport of Nitric Oxide with the Heat-Mass Transfer Analogy Joseph C Muskat, Charles F Babbs, Craig J Goergen, Vitaliy L Rayz To investigate how intravascular transport of nitric oxide (NO)/nitrite varies across arterial scale, we assessed species transport with high-resolution three-dimensional idealized models of bifurcating arteries. Morphological and hemodynamic input parameters such as parent-daughter branching area ratios and flow rates were estimated with available in vivo data. To enhance computational efficiency of the advection-diffusion models in ANSYS Fluent, we utilized the heat-mass transfer analogy through matching nondimensional Schmidt and Prandtl numbers thus allowing useful translation of relative temperature changes to changes in NO/nitrite concentration ([NOx]) at each arterial scale. Convection dominated flows in large arteries result in the formation of near-wall [NOx] boundary layers; however, bifurcations induce scale-dependent mixing of boundary layers with core flow in >200 μm diameter arteries reducing [NOx]. In contrast, NO/nitrite diffusion in arterioles <100 μm diameter raised cross-sectionally averaged [NOx] to the nanomolar range. We investigate the effect of additive propagation of NO/nitrite from large arteries on vasodilation and red blood cell absorption of circulating NO/nitrite. |
Sunday, November 20, 2022 8:39AM - 8:52AM |
A13.00004: Using Procedurally Expanded Discrete Cerebral Vasculature with a Vascular-Porous Model to Simulate Perfusion and Temperature Effects Following Ischaemic Stroke Luke Fulford, Ian Marshall, Joanna M Wardlaw, Prashant Valluri Modelling the flow and temperature effects after ischaemic stroke can be shown to require vasculature with a level of detail not obtainable from conventional imaging techniques. We have developed a method to augment the obtainable cerebral vasculature with additional procedurally generated vasculature, creating a 1D hybrid tree for the arteries and veins. Procedural generation is weighted by the positions of arterial territories and tissue type. It creates vessel networks which functions according to clinical expectations. This is then combined with a 3D porous tissue and our existing Vascular-Porous (VaPor) model to fully simulate the blood flow and temperature distributions in the cerebral geometry, including satisfactory simulation of the ischaemic region. The resulting perfusion profile, including occlusion geometry, and temperature profile are calculated by solving the mass, momentum and energy equations. Good visual agreement is seen between the perfusion profiles obtained with VaPor and those from in-vivo imaging of stroke, including the presence of penumbral tissue. Simulation of stroke allows obstruction of any arterial vessel segment within the base tree and observing the effects. These results show that there can be significant variation in the perfusion after stroke, even for a similarly placed obstruction. Applying our model shows temperature rises in the affected region immediately after stroke, of the order of 0.5 °C. Crucially, our model also indicates that, dependant on location, these temperature profiles can be influenced by external cooling. Meaning that direct brain cooling via the scalp could be more effective than previously thought. |
Sunday, November 20, 2022 8:52AM - 9:05AM |
A13.00005: A lumped parameter model of liver resections for improving surgical outcomes Jeffrey Tithof, Timothy Pruett, Joseph Sushil Rao The liver serves multiple critical functions related to processing and filtering blood which are vital to maintaining homeostasis. This includes extracting and storing nutrients, removing waste products and toxins, and processing alcohol and medications. Numerous diseases, such as cancer and hepatitis, may necessitate liver resection (i.e., surgery in which a portion of the liver is removed). However, the vascular structure of the liver often leads to challenging surgical decisions, especially related to ligation of the hepatic vein which forms the outflow route from the liver. We will present a lumped parameter model of blood flow through the entire liver, resolved down to the length scale of the lobules (functional units of the liver that are about 1 mm in diameter). Our model is parameterized based on clinical measurements, relies on only a single free parameter, and accurately captures established blood perfusion characteristics. We impose variable, realistic liver resections to our model and quantify the associated changes in volume flow rate, average blood velocity, and wall shear stress which we compare to the intact liver. We will highlight novel factors affecting liver perfusion and present predictions of surgical outcomes. Our numerical model can be adapted to patient-specific anatomy and runs on a laptop in minutes, constituting an appreciable step toward a novel computational tool for assisting surgical decisions in liver resection. |
Sunday, November 20, 2022 9:05AM - 9:18AM |
A13.00006: Modeling of Catheter Microsphere Injection for Patient Specific Y-90 Radioembolization Carlos A Ruvalcaba, Emilie Roncali
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Sunday, November 20, 2022 9:18AM - 9:31AM |
A13.00007: The impact of fluid mechanics in liver cell therapies Evangelia Antonopoulou, Melissa R Vieira, Alicia El Haj, Sarah L Waters Cell therapy for liver disease aims to inject donor cells into the vasculature to engraft and regenerate regions of diseased liver. Fluid mechanical stresses are sensed by cells as they transit to the injury site and can lead to upregulation of integrin expression. Integrins are receptors that bind to extracellular matrix, which in turn promotes engraftment of the donor cells into the injured tissue.We combine in silico and in vitro approaches to understand the relationship between fluid flow conditions and the integrin expression. |
Sunday, November 20, 2022 9:31AM - 9:44AM |
A13.00008: Patient-specific modeling of hemodynamic disorders using Physics Informed Neural Networks Rohit Kameshwara Sampath Sai Vuppala, Peetak Mitra, Kalai Ramea Hemodynamic disorders are diseases caused by the altered dynamics of the blood flow in the circulatory system, due to anomalies like aneurysms or plaque deposition, and are one of the leading causes of preventable deaths in the US. Since these disorders are highly patient-specific in nature, building individualized hemodynamic profile models has gained a lot of interest. However, running large ensembles of these realizations with full 3D CFD (Computational Fluid Dynamics) models is computationally expensive. While traditional Data-driven techniques (such as Deep Learning) are computationally cheaper for inference, they typically require large amounts of high-fidelity data for training. Physics Informed Neural Networks (PINNs) overcome this challenge by providing a framework to leverage the underlying knowledge of the governing equations into training the neural network, thereby reducing the need for copious amounts of labelled training data to devise a biologically/physiologically consistent model. In this work, we demonstrate the feasibility of using PINNs to study hemodynamic flow conditions for arteriosclerosis and aneurysms, enabling faster, reliable evaluations of flow patterns for surgical planning and exploring possible medical intervention strategies (such as stents). |
Sunday, November 20, 2022 9:44AM - 9:57AM |
A13.00009: Fluid-Structure Interaction of a Collapsible Thin-Walled Vessel under Steady and Pulsatile Flow Conditions Yan Zhang, Jennifer Schmeling, Sifat K Chowdhury Fluid-structure interactions between pulsatile flow and collapsible vessels are common in physiological systems, such as large veins, pharyngeal canal, and pulmonary airways. The interactions exhibit rich non-linear unsteady behaviors including self-excited oscillations and internal flow instabilities. In this work, experiments were conducted to study the wall deformation and the fluid flow in a thin-walled vessel using the optical method and Particle Image Velocimetry. A Newtonian fluid mixture was used as a blood surrogate and the internal flow is simulated under both steady and pulsatile conditions. Both the internal pressure gradient and the transmural pressure were controlled. Our results suggest the vessel deformation follows Shapiro's tube law under stationary conditions. The maximum collapse location and cross-sectional area shift as Re and transmural pressure change. A critical transmural pressure range exists within which the self-excited oscillations occur. Both chaotic and cyclic oscillations have been observed. Under pulsatile flow conditions, the interaction behavior is significantly altered as a function of Re, Wo, pulsatility index, and transmural pressure. The study provides a benchmark for computational studies of pulsatile flow in complex collapsible vessels. |
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