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 H18: Biological Fluid Dynamics : Cerebral Flows |
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Chair: Kimberly Stevens, Purdue University Room: 400 |
Monday, November 25, 2019 8:00AM - 8:13AM |
H18.00001: Optimum heart rate for brain-heart hemodynamic coupling and its clinical relevancy for neurodegenerative diseases Arian Aghilinejad, Faisal Amlani, Kevin King, Niema Pahlevan Neurodegenerative diseases such as Alzheimer's dementia have reached an epidemic proportion with a significant impact on public health. Disproportionate age-related stiffening of the aorta compared with the carotid arteries is theorized to reduce the protective impedance mismatch at the aorta-carotid interface and affect the regulation of cerebral hemodynamics. Recent clinical data has indicated the existence of a potential link between arterial stiffening, as measured by arch pulse wave velocity (PWV), and Alzheimer's disease. In this study, we used an energy-based analysis of hemodynamic waves to quantify the effect of aortic arch stiffening on pulsatile hemodynamic transmission to cerebral vasculature. A one-dimensional blood flow model of the human vascular network was used to simulate pressure and flow wave propagations in the systemic circulation. Our results show there exists an optimum wave condition---occurring near normal human heart rates---that creates an optimum hemodynamic state for heart-brain coupling and minimizes pulsatile energy transmission to the brain. This is clinically important since excessive pulsatile energy transmission to microvasculature causes end-organ damage that may promote progression of neurodegenerative disease such as Alzheimer's dementia. [Preview Abstract] |
Monday, November 25, 2019 8:13AM - 8:26AM |
H18.00002: Modelling Direct Brain Cooling for Acute Ischaemic Stroke with the Vascular-Porous Model Luke Fulford, Ian Marshall, Peter Andrews, Prashant Valluri Ischaemic stroke is a major cause of death and disability in the world, occurring when a blockage forms in an artery supplying the brain, preventing blood from accessing part of the brain and causing a cascade of events that ultimately cause the death of tissue in the ischaemic region. Reducing the temperature of this tissue has been shown to be beneficial in increasing the treatment window and improving outcomes. Previous modelling studies with vastly idealised geometry have highlighted difficulties in reducing temperatures within the brain using non-invasive means. However by using a model with 1-dimentional vasculature embedded in a 3-dimentional porous tissue, the geometry of the brain and the ischaemic region can be accurately captured. In this work, we simulate a stroke by obstructing a selected vessel in the arterial tree, allowing for varying degrees of severity. By seeking solutions to the mass, momentum and energy equations, we demonstrate that cooling via the scalp has the potential to provide a useful reduction, around 0.5$^{\circ}$C, in temperature within the affected area of the brain. The degree of cooling achievable is dependent on the location of the stroke. [Preview Abstract] |
Monday, November 25, 2019 8:26AM - 8:39AM |
H18.00003: Flow in Porous Media as a Model for Intramural Periarterial Drainage from the Brain. Ketaki Joshi, J. David Schaffer, Paul Chiarot, Peter Huang Accumulation of beta-amyloid proteins in the vasculature of the brain is a characteristic of Alzheimer's disease. One of the pathways to clear these proteins out of the brain is through intramural periarterial drainage (IPAD) along artery walls. There is evidence that the direction of this flow is opposite to that of the arterial blood flow. The periarterial space where IPAD takes place is mostly made up of smooth muscle cells and extracellular matrix. Deformation of the arterial wall boundaries are theorized to drive IPAD. In our earlier work, we reported on a hydrodynamic mechanism for reverse flow through the artery wall that was driven by forward propagating and reflected waves along the boundaries of an open conduit. In our current work, we have expanded our model by incorporating porous media inside the flow channel. We analyzed images of artery deformations in the brains of anesthetized mice provided by Cornell University (N. Nishimura). The quantified boundary deformations of the cerebral arteries are used in numerical simulations to predict the magnitude of the induced IPAD through the porous periarterial space. The role of geometry (i.e. porosity) and permeability on the fluid transport is determined. [Preview Abstract] |
Monday, November 25, 2019 8:39AM - 8:52AM |
H18.00004: Computational Study of Hemodynamic Nature in Patient-Specific Cerebrovasculature with Lenticulostriate Artery under ICA Stenosis Conditions Taehak Kang, Debanjan Mukherjee, Jeong-Min Kim, Kwang-Yeol Park, Jaiyoung Ryu Lenticulostriate arteries play important role in cerebral circulation, especially in basal ganglia region. Deeper understanding of hemodynamic nature of LSA would grant more effective surgical or endovascular treatments. This is the first study to investigate hemodynamic changes in small cerebral artery, namely lenticulostriate artery (LSA), coupled with complete three-dimensional cerebral vasculature under carotid (ICA) stenosis conditions. For patient-specific study, patient CTA data with complete cerebral anatomy is obtained from STOP Stroke database, and computational reconstruction is carried out using open-source package, SimVascular. Petrov-Galerkin formulation is used to solve the fluid domain with pulsatile inflow and lumped three-element Windkessel outlet conditions. NASCET-based stenosis cases are applied to internal carotid artery for all patient-specific models, and their three-dimensional hemodynamic structure is visualized for comparison. We present the results in key hemodynamic properties and indexes such as VFR, MAP, and OSI. As a result, significant hemodynamic changes are shown in LSA and its cerebrovasculature under progressive ICA stenosis conditions. [Preview Abstract] |
Monday, November 25, 2019 8:52AM - 9:05AM |
H18.00005: Cerebral Vascular Super Resolution Imaging and Blood Flow Measurement Using Ultrasound Enhanced Particle Tracking Velocimetry. Zeng Zhang, Joseph Katz, Misun Hwang, Todd Kilbaugh Hypoxic ischemic encephalopathy is a major cause of neonatal death. It is usually initiated with ischemia and hypoxia followed by blood reperfusion leading to brain damage. While conventional MRI gives hemodynamic information, it cannot be used for cerebral histology, which is vital for understanding the mechanism of reperfusion, and developing appropriate therapies. Therefore, contrast enhanced ultrasound particle tracking velocimetry (echo-PTV) is utilized to generate maps of the cerebral vasculature and blood flow velocity simultaneously. The microbubbles are injected intravenously, and the raw ultrasound images are collected using clinical systems. Blind deconvolution, local background removal, and modified histogram equalization are applied to enhance the image and map the bubble spatial distribution. Subsequently, particle tracking is initiated using cross-correlation and updated with a Kalman filter to calculate the velocity field. The microvascular map is generated by a superposition of the bubble trajectories that can be tracked for over 5 frames. The larger vessels are represented by integrating the enhanced images over the acquisition time. Results show 27{\%} and 48{\%} decrease in blood velocity and micro-vessels number with flow, respectively, 3 hours after ischemia. [Preview Abstract] |
Monday, November 25, 2019 9:05AM - 9:18AM |
H18.00006: Hemodynamics of cerebral aneurysms as cavity flow on a curved vessel. Effect of inertia, curvature, pulsatility and treatment with flow diverting stents Fanette Chassagne, Michael C. Barbour, Venkat K. Chivukula, Laurel M. Marsh, Michael R. Levitt, Alberto Aliseda Flow in cerebral aneurysms can be described as flow in a cavity on a curved vessel, with the effects of inertia, curvature and pulsatility providing the conditions under which flow separates on the leading edge of the cavity and recirculate inside the sac against the parent vessel flow, for part or all of the cardiac cycle. This strong coherent vortex in the aneurysm can provide a quantitative metric to explain the persistence of aneurysmal flow after treatment with flow diverting stents (FDS). These high porosity meshes lower the flowrate into the sac promoting the formation of a thrombus. The aim of this study is to investigate the flow pre- and post-treatment with FDS, to understand its variation with flow conditions and aneurysm geometry. Flow inside cerebral aneurysm phantoms with varying parent vessel curvature, neck size and sac aspect ratio is measured with PIV. The hemodynamics in the sac pre- and post FDS treatment are characterized for different waveforms. The results show parent vessel curvature dominates hemodynamics and that increasing Dean number decreases the effect of the FDS treatment. This is due to a combination of changes in parent vessel hemodynamics at the aneurysm leading edge combined with the parent vessel curvature impact on stent porosity. [Preview Abstract] |
Monday, November 25, 2019 9:18AM - 9:31AM |
H18.00007: Coils vs stents: CFD investigation of the mechanisms of healing for two endovascular therapies in cerebral aneurysms Michael Barbour, Laurel Marsh, Fanette Chassagne, Venkat Keshav Chivukula, Cory Kelly, Sam Levy, Michael Levitt, Louis Kim, Alberto Aliseda Cerebral aneurysm treatment seeks to avoid the risk of rupture by excluding the aneurysmal sac from the circulation. Coiling and stenting are two forms of minimally invasive endovascular treatment that, while increasingly popular, present a non-negligible risk of incomplete embolization of the aneurysm. The placement of flow-diverting stents (FDS) or coils leads to aggregation of activated platelet and thrombus formation. A stable thrombus that fully occludes the aneurysm marks a successful treatment as it excludes the aneurysmal sac from hemodynamic stresses and minimizes the risk of rupture. There is currently no accurate method to predict the outcome of either endovascular therapy. We present in silico studies that show the hemodynamics changes, pre- to post-treatment, for both forms of treatment trend in opposite directions. We consider the treatment types separately to find certain changes in Eulerian variables are statistically different between the successful and unsuccessful treatments. The successfully coiled aneurysm cases were marked by a higher overall increase in the neck plane shear than the failed cases. While one of the most significant metrics for predicting a successful FDS treatment is the change in flowrate entering the aneurysm during systole. [Preview Abstract] |
Monday, November 25, 2019 9:31AM - 9:44AM |
H18.00008: Coils vs stents: Lagrangian-tracking investigation of the mechanisms of healing for endovascular therapies in cerebral aneurysms Laurel Marsh, Michael Barbour, Fanette Chassagne, Venkat Keshav Chivukula, Cory Kelly, Sam Levy, Micheal Levitt, Louis Kim, Alberto Aliseda We study the success of treatment in endovascularly treated cerebral aneurysms by means of Lagrangian tracking of platelets in CFD simulations of blood flow in patient-specific models. Flow-diverting stents (FDS) or coils can lead to aggregation of activated platelets and formation of a stable thrombus that fully occludes the aneurysm. However, there is currently no accurate method to predict the outcome of either endovascular therapy. We propose a series of Lagrangian metrics, based on trajectories of tracer particles introduced in the intracerebral vasculature, to understand the hemodynamics conditions that lead to stable thrombus formation as opposed to conditions that lead to incomplete embolization. We consider the two forms of therapies separately, using platelet residence time and shear history to complement Eulerian metrics that have traditionally been used to understand hemodynamics in intracranial aneurysms: Wall Shear Stress, WSS gradient, flow rate through the neck. We develop accurate predictors of outcomes for each endovascular treatment, using a large population of \textgreater 50 patients to validate them. your abstract body. [Preview Abstract] |
Monday, November 25, 2019 9:44AM - 9:57AM |
H18.00009: Difference in Hemodynamic Parameters Between Cerebral Aneurysms Models with Truncated Parent Arteries and with Parent Arteries Extending to the Carotid Siphon Yuya Uchiyama, Hiroyuki Takao, Soichiro Fujimura, Hiroshi Ohno, Felicitas Detmer, Sara Hadad, Setareh Salimi, Fernando Mut, Koji Fukudome, Juan Cebral, Yuichi Murayama, Makoto Yamamoto Recently, CFD simulations are used to study cerebral aneurysm pathologies. In the human anterior circulation, the internal carotid artery (ICA) has a particular bent section called carotid siphon. However, vessels distal and proximal of aneurysms are often truncated to perform simulations although they can have an effect on blood flow behavior. In this study, we compared hemodynamic parameters in models with and without the siphon. We selected 21 aneurysms located in distal ICA. For each case, we created a model with the siphon (‘longer model’) and another without it (‘shorter model’). We performed pulsatile blood flow simulation in all the cases, and then calculated and compared 20 typical aneurysm hemodynamic parameters in each model. Results showed that some hemodynamic parameters were different between the two models. Particularly, WSS was on average 60.6\% smaller in shorter models compared to longer models. In conclusion, the inclusion of the carotid siphon to the model is important to represent the hemodynamic environment within the aneurysm. [Preview Abstract] |
Monday, November 25, 2019 9:57AM - 10:10AM |
H18.00010: Quantifying unstable flows in sidewall aneurysms at internal carotid arteries Trung Le, Elizabeth Eidenschink, Alexander Drofa Complex, unstable flow has been linked to aneurysm growth and rupture. Our previous works (Le et al., J. Biomech. Engr., 2010 and Le et al., Annals Biomedical Eng., 2013) have shown a possible transition from the stable mode (cavity) to the unstable mode (vortex ring). We have proposed the use of a non-dimensional index called ‘Aneurysm Number’ to characterize this transition (Le et al., 2013). However, the quantification of such a transition is lacking. Currently, there has been no efforts in quantifying unstable flows in intracranial aneurysms, which is essential in stratifying not only rupture risks, but also to guide clinical management. In this work, the aneurysmal geometries from six patients at Sanford Health, North Dakota are reconstructed from Magnetic Resonance Angiogram and Digital Substraction Angiogram data. Using our in-house CFD code (Virtual Flow Simulator), high-resolution flow data is obtained. In this work, we propose the use of enstrophy mapping as a potential index to stratify aneurysm flows. We show that this type of mapping is able to differentiate stable from unstable modes in patient-specific anatomies. We also provide evidence on the link of ‘Aneurysm Number’ and enstrophy mapping. [Preview Abstract] |
Monday, November 25, 2019 10:10AM - 10:23AM |
H18.00011: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 10:23AM - 10:36AM |
H18.00012: Patient-Specific Computational Modeling of Cerebrovascular AVM-related Aneurysms Kimberly A. Stevens, Aaron A. Cohen-Gadol, Ivan C. Christov, Vitaliy L. Rayz An arteriovenous malformation (AVM) is a pathological condition where an abnormal tangle of vessels connects arteries to veins, bypassing the capillary bed. The decreased flow resistance can lead to increased flow in the vessels feeding the AVM, thought to be responsible for the pathogenesis of flow-related aneurysms. To investigate the relationship between AVMs and flow-related aneurysms, we created image-based computational fluid dynamic models of five flow-related cerebral aneurysms coupled with reduced-order lumped-parameter network models representing the AVMs. Vascular geometries for computational models are generated from CT data obtained from IU School of Medicine, and the blood flow within the geometry is computed using an open-source modeling platform, SimVascular. Once created, the model boundary conditions are modified to simulate AVM treatment and predict postoperative flow conditions. Calculated hemodynamic parameters known to influence arterial wall remodeling and intra-luminal thrombus deposition, such as the wall shear stress and oscillatory shear index, are compared between pre- and post-operative flow scenarios. Results indicate that hyperdynamic flow upstream of the AVM leads to elevated wall shear stress, which can be mitigated following AVM treatment. [Preview Abstract] |
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