Current Search: thrombus (x)
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Title
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UNDERSTANDING AND MODELING PATHWAYS TO THROMBOSIS.
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Creator
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Seligson, John, Kassab, Alain, University of Central Florida
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Abstract / Description
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Intra-vessel thrombosis leads to serious problems in patient health. Coagulation can constrict blood flow and induce myocardial infarction or stroke. Hemodynamic factors in blood flow promote and inhibit the coagulation cascade. Mechanically, high shear stress has been shown to promote platelet activation while laminar flow maintains plasma layer separation of platelets and endothelial cells, preventing coagulation. These relationships are studied experimentally, however, physical properties...
Show moreIntra-vessel thrombosis leads to serious problems in patient health. Coagulation can constrict blood flow and induce myocardial infarction or stroke. Hemodynamic factors in blood flow promote and inhibit the coagulation cascade. Mechanically, high shear stress has been shown to promote platelet activation while laminar flow maintains plasma layer separation of platelets and endothelial cells, preventing coagulation. These relationships are studied experimentally, however, physical properties of thrombi, such as density and viscosity, are lacking in data, preventing a comprehensive simulation of thrombus interaction. This study incorporates experimental findings from literature to compile a characteristic mechanical property data set for use in thrombosis simulation. The focus of this study's simulation explored how thrombi interact between other thrombi and vessel walls via Volume of Fluid method. The ability to predict thrombosis under specific hemodynamic conditions was also a feature of the data collection. Using patient specific vessel geometry, the findings in this study can be applied to simulate thrombosis scenarios. The possible applications of such a simulation include a more precise method for estimation of patient myocardial infarction or stroke risk and a possible analysis of vessel geometry modification under surgery.
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Date Issued
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2015
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Identifier
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CFH0004837, ucf:45440
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004837
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Title
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Transient Multi-scale Computational Fluid Dynamics (CFD) Model for Thrombus Tracking in an Assit Device Vascular Bed.
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Creator
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Osorio, Ruben, Kassab, Alain, Divo, Eduardo, Ilie, Marcel, University of Central Florida
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Abstract / Description
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Heart failure occurs when the heart is not capable to pump blood at a sufficient rate to meet the demands of the body. Depending on the health of the heart, doctors may recommend a heart transplant, but finding a suitable donor is often a long duration process and the patient might be at an advance condition or the patient is not adequate for a heart transplant. In such cases Ventricular assist devices (VAD) are implemented. The purpose of a VAD is to aid the heart to pump the correct amount...
Show moreHeart failure occurs when the heart is not capable to pump blood at a sufficient rate to meet the demands of the body. Depending on the health of the heart, doctors may recommend a heart transplant, but finding a suitable donor is often a long duration process and the patient might be at an advance condition or the patient is not adequate for a heart transplant. In such cases Ventricular assist devices (VAD) are implemented. The purpose of a VAD is to aid the heart to pump the correct amount of blood, by doing so it relives the load that is put on the heart while giving the patient a chance for recovery. This study focuses on observing the hemodynamic effects of implementing a left ventricular assist device (LVAD) along the aortic arch and main arteries. Thrombi creation and transportation is other subject included in the study, due to the fact that thrombi can obstruct blood flow to critical arteries, manly carotid and vertebral. Occlusion of these can lead to a stroke with devastating effects on the neurocognitive functions and even death.A multi-scale CFD analysis a patient specific geometry model is used as well as a lumped system which provides the correct conditions in order to simulate the whole cardiovascular system. The main goal of the study is to understand the difference in flow behavior created by the unsteady pulsatile boundary conditions. The model described in this work has a total cardiac output of 7.0 Liters/ minute, this for a healthy heart. Two cardiac output splits are used to simulate heart failure conditions. The first split consists of 5 Liters/minute flowing through the LVAD cannula and 2 Liters/minute via the aortic root. The second scenario is when heartivfailure is critical, meaning that zero flow is being output by the left ventricle, thus a split of 7 Liter/minute trough the LVAD cannula and 0 Liters/minute traveling through the aortic root. A statistical analysis for the thrombi motion throughout the patient aortic arch was performed in order to quantify the influence that pulsatile flow has on the particles being track. Spherical particles of 2mm, 4mm and 5mm were released and accounted in the statistical analysis for each of the two split configurations. The study focuses on particles that escaped on the outlet boundaries of the upper arteries (Right Carotid, Left Carotid, and Vertebral). Results exhibit the statistical comparison of means for each particle diameter as well as for the overall probability for the steady and unsteady flow condition.
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Date Issued
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2013
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Identifier
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CFE0004905, ucf:49633
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004905
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Title
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COMPUTATIONAL FLUID DYNAMICS INVESTIGATION OF THE ORIENTATION OF A PEDIATRIC LEFT VENTRICLE ASSIST DEVICE CANNULA TO REDUCE STROKE EVENTS.
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Creator
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Guimond, Stephen, Kassab, Alain, University of Central Florida
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Abstract / Description
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Ventricle Assist Devices (VADs), which are typically either axial or centrifugal flow pumps implanted on the aortic arch, have been used to support patients who are awaiting cardiac transplantation. Success of the apparatus in the short term has led to long term use. Despite anticoagulation measures, blood clots (thrombi) have been known to form in the device itself or inside of the heart. The Ventricle Assist Devices supply blood flow via a conduit (cannula) implanted on the ascending aorta....
Show moreVentricle Assist Devices (VADs), which are typically either axial or centrifugal flow pumps implanted on the aortic arch, have been used to support patients who are awaiting cardiac transplantation. Success of the apparatus in the short term has led to long term use. Despite anticoagulation measures, blood clots (thrombi) have been known to form in the device itself or inside of the heart. The Ventricle Assist Devices supply blood flow via a conduit (cannula) implanted on the ascending aorta. Currently, the implantation angle of the VAD cannula is not taken into consideration. Since the VADs supply a significant amount of blood flow to the aorta, the implantation angle can greatly affect the trajectory of the formed thrombi as well as the cardiac flow field inside of the aortic arch. This study aims to vary the implantation angle of a pediatric Left Ventricle Assist Device (LVAD) through a series of computational fluid dynamics (CFD) software simulations focusing on the aortic arch and its branching arteries of a 20 kg pediatric patient in order to reduce the occurrence of stroke.
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Date Issued
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2012
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Identifier
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CFH0004305, ucf:45044
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004305
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Title
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Multi-scale fluid-structure interaction model analysis of patient-specific geometry for optimization of lvad outflow graft implantation: an investigation aimed at reducing stroke risk.
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Creator
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Prather, Ray, Kassab, Alain, Mansy, Hansen, Bai, Yuanli, Divo, Eduardo, DeCampli, William, University of Central Florida
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Abstract / Description
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A Left Ventricular Assist Device (LVAD), is a mechanical pump capable of(&)nbsp;providing circulatory myocardium relief when used as bridge-to-transplantation by reducing the workload of a failing heart, with the additional bonus of allowing for cardiac recovery when used as destination therapy. The newer generations of continuous flow VADs are essentially axial or radial flow pumps, and while these devices are capable their efficiency depends upon fluid composition and flow field patterns....
Show moreA Left Ventricular Assist Device (LVAD), is a mechanical pump capable of(&)nbsp;providing circulatory myocardium relief when used as bridge-to-transplantation by reducing the workload of a failing heart, with the additional bonus of allowing for cardiac recovery when used as destination therapy. The newer generations of continuous flow VADs are essentially axial or radial flow pumps, and while these devices are capable their efficiency depends upon fluid composition and flow field patterns. The most devastating complication of VAD therapy is caused by embolization of thrombi formed within the LVAD or inside the heart into the brain leading to stroke. Anticoagulation management and improved LVADs design has reduced stroke incidence, however, investigators have recently reported the incidence of thromboembolic cerebral events is still significant and ranges from 14% to 47% over a period of 6-12 months. Blood clots may cause obstruction of critical vessels, such as cerebral arteries, reducing brain oxygenation and resulting in devastating consequences like major neurocognitive malfunction and complications which can be fatal.The hypothesis that incidence of stroke can be significantly reduced by adjusting the VAD outflow cannula implantation to direct dislodged thrombi away from the cerebral vessels has been recently supported by a series of steady flow computations assuming rigid vessel walls for the vasculature. Such studies have shown as much as a 50% reduction in embolization rates depending on outflow cannula implantation. In this study, a pulsatile fully compliant vessel wall model is developed to further establish this hypothesis. A time-dependent multi-scale Eulerian Computational Fluid Dynamics (CFD) analysis of patient-specific geometry models of the VAD-bed vasculature is coupled with a 3D Finite Element Analysis (FEA) of the mechanical response of the vascular walls to establish the VAD assisted hemodynamics. A Lagrangian particle tracking algorithm is used to determine the embolization rates of thrombi emanating from the cannula or other possible thrombogenic locations such as the aortic root. This multiscale Eulerian-Lagrangian pulsatile fluid-structure coupled paradigm allows for a fully realistic model of the hemodynamics of interest. The patient-specific geometries obtained from CT scan are implemented into the numerical domain in two modes. In the 3D CFD portion of the problem, the geometry accounts solely for the flow volume where the fluid is modelled as constant density and non-Newtonian under laminar pulsatile flow conditions. The blood-thrombus ensemble in treated as a two-phase flow, handled by an Eulerian-Lagrangian coupled scheme to solve the flow field and track particle transport. Thrombi are modelled as constant density spherical particles. Particle interactions are limited to particle-to-wall and particle-to-fluid, while particle-to-particle interaction are neglected for statistical purposes. On the other hand, with the help of Computer Aided Design (CAD) software a patient-specific aortic wall geometry with variable wall thickness is brought into the numerical domain. FEA is applied to determine the aortic wall cyclic displacement under hydrodynamic loads. To properly account for wall deformation, the arterial wall tissue incorporates a hyperelastic material model based on the anisotropic Holzapfel model for arteries. This paradigm is referred to as Fluid Structure Interaction (FSI) and allows structural analysis in conjunction with flow investigation to further monitor pathological flow patterns. The FSI model is driven by time dependent flow and pressure boundary conditions imposed at the boundaries of the 3D computational domain through a 50 degree of freedom 0D lumped parameter model (LPM) electric circuit analog of the peripheral VAD-assisted circulation.Results are presented for a simple vessel model of the ascending aorta to validate the anisotropic fiber orientation implementation. Arterial wall dilation is measured between 5-20% in the range reported in literature. Hemodynamics of the VAD assisted flow in a patient-derived geometry computed using rigid vessels walls are compared to those for a linearly elastic vessel wall model and a hyperelastic anisotropic vessel wall model. Moreover, the thromboembolization rates are presented and compared for pulsatile hemodynamics in rigid and compliant wall models. Pulsatile flow solutions for embolization probabilities corroborate the hypothesis that tailoring the LVAD cannula implantation configuration can significantly reduce thromboembolization rates, and this is consistent with indications from previous steady-flow calculations.
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Date Issued
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2018
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Identifier
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CFE0007077, ucf:52017
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0007077