Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session L05: Physiological Fluid Mechanics III: Large Vessels |
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Chair: Robert Kunz, Pennsylvania State University Room: Ballroom E |
Monday, November 25, 2024 8:00AM - 8:13AM |
L05.00001: Evaluating the effect of morphology on cerebral aneurysm hemodynamics Cheng Peng, Baha Al-deen T El-khader, Ephraim W Church, Melissa Brindise The morphology of intracranial aneurysms (IA) is known to affect the hemodynamics and risk of growth and progression of the IA. Prior studies have shown that the shape-based factors of aspect ratio, diameter, and ellipticity index are highly correlated with IA rupture. This study aims to evaluate the sensitivity of hemodynamic parameters to changes in IA morphology. We established cases with varying aneurysm morphologies, adopting geometries from patient-specific models. These aneurysms were evaluated using computational fluid dynamics (CFD) simulations to analyze relevant hemodynamic parameters, including pressure and wall shear stress (WSS). The CFD results were compared with existing particle tracking velocimetry (PTV) data for validation. This analysis assesses the sensitivity of key hemodynamic parameters—such as wall shear stress, oscillatory shear index, etc.—to IA morphology, providing detailed insights into the hemodynamics of differently shaped IAs and establishing a baseline for diagnosing and predicting IA rupture risk based on morphology. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L05.00002: Hemodynamic and Morphological Factors Influencing Wall Integrity in Intracranial Aneurysms: A Comparative Study of Thin and Thick-Walled Aneurysms Yogesh Karnam, Anne M Robertson, Juan R Cebral While often asymptomatic until rupture, Intracranial Aneurysms (IAs) can lead to subarachnoid hemorrhage, thus posing significant challenges. Clinical evaluation of IAs typically considers size and morphology, but hemodynamics-induced mechanisms responsible for the thinning or thickening of the wall, which can lead to wall weakening and failure, remain poorly understood. To elucidate such mechanisms, we analyzed surgical videos of clipped IAs to identify regions with different wall appearances and assigned them to group A: IAs with thin walls (n=24) or B: IAs with thick walls (n=12). Then, we compared shape and flow factors derived from CFD models reconstructed from 3D images. Results show statistically significant differences between groups A and B for wall shear stress (WSS) (p=0.06, OR=0.95), WSS gradient in neck zone (p=0.03, OR=0.98), flow impingement in dome zone (p=0.03, OR=1.05), vortex core line length (flow complexity) (p=0.03, OR=1.75), bottleneck factor (width/neck diameter) (p=0.02, OR=16.9), surface curvature (p=0.03, OR=1.7), and volume to ostium ratio (volume/neck area) (p=0.04, OR=3.02). In summary, IAs in group A were smaller, with wider necks, and were exposed to higher WSS and WSS gradients, leading to thinner walls. In contrast, IAs in group B were larger with smaller necks and had lower WSS and WSS gradients combined with flow impingements at the dome, leading to thicker walls. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L05.00003: Assessing high-frequency fluctuations in intracranial aneurysms using direct numerical simulation, conventional computational fluid dynamics and particle tracking velocimetry Jana E Korte, Baha Al-deen T El-khader, Abouelmagd Abdelsamie, Melissa Brindise, Philipp Berg An intracranial aneurysm (IA) is an artery expansion in the neurovascular system (NVS), carrying the risk of rupture, which can lead to subarachnoid hemorrhage. Despite the laminar flow behavior in the NVS, recent studies have detected high-frequency fluctuations (HFFs) in IAs. In this study three modalities were evaluated on their ability to capture HFF. Experimentally, particle tracking velocimetry (PT) and computationally direct numerical simulations (DNS) using an in-house solver and conventional computational fluid dynamics using STAR CCM+ (STAR) were applied. An aneurysm model was 3D printed for PT and a CT scan was captured, which was then processed for simulations. Three simulations/experiments were performed using three varying heart rates as inflow. Velocity and vorticity distribution was evaluated, and specific probes chosen for transient analysis. Results were analyzed to qualitatively and quantitatively validate the simulations with the PT and to compare the three modalities regarding their effectiveness to capture HFFs. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L05.00004: Hemodynamic Simulation for Safe Surgical Clipping of Intracranial Aneurysms: Temporary Strangulation of the Common Carotid Artery Sangwon Ryu, Kyoungmin Jang, Taekkyun Nam, Jaiyoung Ryu Intracranial aneurysms (IAs) refer to a weakening and abnormal ballooning of blood vessel walls. Safe surgical clipping to treat IAs requires reducing aneurysmal pressure. We explored a method involving the temporary strangulation of the ipsilateral common carotid artery (CCA) to decrease pressure at middle cerebral artery (MCA) aneurysms. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L05.00005: Abstract Withdrawn
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Monday, November 25, 2024 9:05AM - 9:18AM |
L05.00006: Enhanced Hemodynamics in Patient-Specific Cerebral Aneurysms Due to the Impact of Body Movement: An In-Vitro Study Rahul Raju S, Hritesh Singh, Ryan T Schuster, Zhongwang Dou We aim to understand how human body movement impacts the hemodynamics of cerebral aneurysms due to the physical motion of the vessel wall, beyond typical physiological responses. We first employ a high-speed camera to capture human head movement. Subsequently, we perform in-vitro hemodynamics measurements in a cerebral aneurysm phantom model using a high-speed PIV system on a six-degree-of-freedom motion simulation platform. Three different Patient-specific cerebral aneurysm models are utilized, and different inlet blood flow conditions are tested. We explore and verify the effects of three types of body movements: Simple Harmonic Motion, Single Jump, and Continuous Jumping Motion. In the control group, we measure hemodynamics when the motion simulation platform is at rest. In the treatment groups, hemodynamics measurement and body movement replaying are simultaneously conducted under identical inlet flow conditions in both simplified and patient-specific geometries. We observed clear differences in flow field and wall shear stress between these groups. This study suggests that, besides physiological responses, body movement also physically contributes to intense hemodynamic changes that need to be considered during the design and verification of any drug or biomedical device. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L05.00007: Measurement of blood flow velocity using temporally-modulated contrast injection based on Digital Subtraction Angiography Hongtao Qian, Yanlin Chen, Cheng Li Real-time hemodynamic information is closely related to the pathophysiology of vascular diseases. By tracking contrast agent concentration, digital subtraction angiography (DSA) can provide quantitative blood flow measurements. Traditional methods typically employ fixed-rate contrast agent injection and the resulting contrast concentration oscillation is due to the inherent pulsatility of the cardiac cycle. Such method is limited in its robustness in distal vascular regions. In the current study, a temporally-modulated contrast injection is generated using a programmable syringe pump. This method is benchmarked in a straight 4 mm diameter vascular model with prescribed constant blood flow rate. The blood-mimicking fluid was prepared from glycerol, distilled water, and ethanol. Signal quality was evaluated at various injection frequencies (0.5 Hz - 4 Hz) using so-called sideband ratio, with 1 Hz identified as optimal. The velocity profile in the blood vessel, derived by applying the shifted least squares algorithm to the concentration curve between any two points at different radial positions of the vessel, matches well with the results from dye tracking and PIV, which serve as measurement benchmarks. Flow velocity measurement was also performed in a patient-specific intracranial artery model, with a total flow rate measurement error of 8.3%. This study presents valuable data for developing a commercial medical device capable of generating contrast agent pulsatility for flow quantification during standard DSA procedures. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L05.00008: In Coronary Artery, Laminar Flow Preserves Stability and Resonance (Combined Vibrations from two Sources) Precipitates Acute Coronary Syndrome: Analysis of In-Vivo Coronary Flow from a Fluid Mechanics Perspective Khiem Ngo, Thach N NGUYEN, Michael Gibson, Nga N Nguyen, Tam Tran The cardiovascular system is conceptualized as a network of pump and pipes. Using a novel angiographic technique, coronary laminar or turbulent, antegrade or retrograde flows could be identified and recorded. Patients with unstable angina who presented to the cardiac catheterization laboratories were screened; those with moderate lesions on their angiograms were included. The aim was to investigate which flow patterns contributed to the stability, regression, or progression of these moderate lesions. A total of 53 patients were included. In 35 patients, the antegrade flow across the lesion was laminar, with no retrograde flow. These patients remained stable if their blood pressure and hyperlipidemia were well controlled. In contrast, the 18 patients whose lesions exhibited retrograde and turbulent flow became unstable and required interventions. Further investigation revealed that the retrograde flow behaved similarly to a pressure wave in the water hammer shock phenomenon. Due to repetitive contractions of the left ventricle during systole and dilation in diastole, axial vibrations occurred in the coronary blood column. When the coronary blood vibration frequency (in its retrograde direction) matched the natural frequency of coronary artery, resonance occured at the transition zone from diastole to systole, causing turbulent flow, rupturing the cap of coronary plaques. The images of these phenomena are strong evidences linking fluid mechanic event to acute coronary syndrome (or heart attack). |
Monday, November 25, 2024 9:44AM - 9:57AM |
L05.00009: Customized Bypass Grafting via Density-Based Topology Optimization: A Hemodynamic Perspective Gianmarco Boscolo, Stefano Lanzoni, Paolo Peruzzo The present study proposes a density-based topology optimization model and evaluates its effectiveness in designing an aorto-coronary bypass. Current literature in bypass design often relies on initial guess solutions iteratively refined with numerical simulations. In contrast, our approach eliminates dependence on arbitrary initial configurations by deriving optimal geometry through the minimization of a functional directly linked to the hydrodynamics within the bypass. This functional is formulated to reduce blood energy dissipation and vorticity, thereby mitigating cardiac pressure overload and preventing recirculation zones that could lead to thrombosis. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L05.00010: Stabilization of Platelet Aggregates in High Shear Rate Flows by Von Willebrand Factor Keshav B Patel, Jian Du, Aaron L Fogelson Arterial blood vessels vary widely in geometry and flow properties. Even in high shear rate environments, when an injury occurs to the vessel wall, platelets must be recruited to prevent the loss of blood. Stenotic arteries can also give rise to structures where platelet aggregation can occur deleteriously. In both cases, the mechanically sensitive polymeric protein Von Willebrand Factor (vWF) mediates the initial deposition of platelets to the growing aggregate. We present a dynamical systems model to study the average mechanical and chemical structure of an aggregate. We consider the aggregate as a porous media whose porosity and height change as platelets deposit. The drag force imparted on the aggregate is felt by all bound platelets, affecting the rate at which platelet-platelet crosslinks break. We find that as shear rate varies, inclusion of platelet-vWF-platelet crosslinking stabilizes the aggregate not only by increasing the total number of crosslinks, but also by changing the overall structure of the aggregate to reduce the drag force per platelet. These results have implications for aggregation in stenotic regions as well as in diseases such as Von Willebrand's Disease. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L05.00011: Integrating Hemodynamics into Predictive Modeling of In-Stent Restenosis: A Computational Study Paolo Peruzzo, Jacopo Del Ferraro, Stefano Lanzoni The influence of hemodynamics has often been underestimated in mathematical models that replicate the restenosis process in stented arteries. This oversight has limited our understanding of the complex interactions between blood flow and arterial wall responses. This work aims to fill this gap by introducing a simplified model of tissue growth influenced by the distribution of mean shear stress on the vessel wall. Through an iterative series of three-dimensional Computational Fluid Dynamics simulations applied to idealized coronary and femoral arteries, along with a semi-empirical parametrization of endothelium growth, we demonstrated that the progression of restenosis can be accurately modeled and distinguished based on the intensity of time-varying flow velocities. |
Monday, November 25, 2024 10:23AM - 10:36AM |
L05.00012: Effect of spiral artery remodeling on the shear stresses acting on the placental villi structure Armita Najmi, Noelia Grande Gutiérrez During pregnancy, the maternal uterine vasculature undergoes significant remodeling. Histopathological studies have shown that incomplete spiral artery (SA) remodeling is related to pregnancy disorders. The inaccessibility of the placenta to invasive measurements and the limitations of in vivo imaging have hindered our understanding of its development. Computational simulations provide an opportunity to investigate how SA remodeling affects placenta microstructure. We studied the effect of SA remodeling on uteroplacental hemodynamics. Then, we related changes in macroscale hemodynamics to microscale shear stresses (SS) on the placental villi. We computationally modeled a placentone (macroscale model), the placenta functional unit, consisting of a SA, veins, a cavity and a dense-villi region. To reduce the computational cost, we modeled the dense-villi region as a porous medium. Based on the flow field obtained from these simulations, we modeled flow around intermediate villi (microscale model) to quantify SS on the villi surface. Less SA remodeling corresponded with higher velocities in the intervillous space and resulted in higher SS on the villi structure, which can be detrimental. To conclude, our computational model provides a quantitative analysis of the SA remodeling impact on microscale SS acting on the villi structure. Fluid SS on the intermediate villi obtained from our simulations can inform experiments to study their effect on the development or malformation of placental villi. |
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