|
|
Application of finite element method to real problems in hemodynamics.
Švihlová, Helena ; Hron, Jaroslav (advisor) ; Dolejší, Vít (referee)
The incompressible fluid flow around the geometries of cerebral artery aneurysms is studied in this thesis. The aneurysm is a local extension of a vessel. This disease is dangerous only in the case of rupture. Then the blood is released into the brain. The need of accurate computation of the velocity and pressure fields in this geometries is motivated exactly by the question which aneurysm has tendency to rupture. The finite element method (FEM) is used for the computation of the flow. A good domain discretization is one of the main step in FEM. Modern computed tomography is able to produce series of the two- dimensional images and it is necessary to create an appropriate three-dimensional model of the tissue. This thesis includes the description of the mesh generation and the ways to smooth and improve the meshes. In the theoretical part the equations of fluid flow are formulated. A suitability of a choice of boundary conditions is discussed. Weak formulation for the equations and its discretization are presented. In the practical part velocity and pressure fields are computed by the various finite elements. Wall shear stress which plays an important role in the evolution of an aneurysm is also computed on the introduced meshes. Comparison of mesh smoothing filters, used finite elements and used...
|
|
|
Projection method applied to modelling blood flow in cerebral aneurysm
Hrnčíř, Jakub ; Hron, Jaroslav (advisor) ; Knobloch, Petr (referee)
This thesis is motivated by a problem of cerebral aneurysms, which are abnormal bulges on the arteries which supply blood for our brain. These aneurysms can rupture and cause death or permanent neurological deficits. To study the evolution of aneurysms and assess the risk of rupture, mathematical modelling might be used to compute otherwise unobtainable information about blood flow inside the aneurysm. For this reason it is essential to be able to model blood flow in sufficiently high resolution. A goal of this thesis was to implement standard projection method for the solution of unsteady incompressible Navier-Stokes equations using the free finite element software FEniCS to create a working code adjusted to the need of this particular application. The incremental pressure correction scheme was chosen. Various shortcomings of this method are described and a proper choice of boundary conditions and other implementation issues are discussed. A comparison of computed important hemodynamic indicator wall shear stress using new and previously used solution approach are compared. A test of the new code for parallel efficiency and performance on finer meshes for a real medical case was conducted. Powered by TCPDF (www.tcpdf.org)
|
|
|
Blood flow modeling in arterial stenosis.
Matajová, Adéla ; Hron, Jaroslav (advisor) ; Dolejší, Vít (referee)
Arterial stenosis is a disease characterized by the buildup of a waxy substance inside the artery, which is associated with certain risks. It is difficult to eval- uate the severity of the stenosis, yet the diagnosis can become more accurate using computational fluid dynamics simulations. The present thesis introduces and applies the model of hemodynamics based on the Navier-Stokes equations, implemented in the FEniCS software employing the finite element method. The main focus lies on the prescription of the boundary condition at the outlet of the computational domain. The impact of the outlet boundary condition on medically significant quantities such as the wall shear stress is analyzed in a two- dimensional benchmark case. It appears that the right choice of the boundary condition is fundamental, in particular when vortices occur and propagate across the outlet boundary. The next part of the work is dedicated to the prescrip- tion of the outflow rate in the case of more than one outlet, corresponding to an artery branching inside the computational domain. The physically meaningful flux distribution is derived introducing Murray's law and its extension. Finally, the blood flow is simulated in a three-dimensional geometry of a patient-specific carotid artery. 1
|
|
|
Hemodynamic optimalization in hepatic recection
Zatloukal, Jan ; Pradl, Richard (advisor) ; Cvachovec, Karel (referee) ; Málek, Jiří (referee)
Lowering of central venous pressure in hepatic surgery is nowadays widely recommended and used procedure. Low central venous pressure anesthesia is associated with decreased blood loss and improved clinical outcome. There are several approaches how to reach low central venous pressure. Till now none of them is recommended as superior in terms of patient safety and clinical outcome. Concurrently there is still debate if to use the low central venous pressure anesthesia principle or if it could be replaced with a principle of anesthesia with high stroke volume variation (or another dynamic preload parameter) with the use of a more sophisticated hemodynamic monitoring method. Results of our study didn't show any significant difference between two approaches used for reduction of central venous pressure, but suggest that the principle of low central venous pressure anesthesia could be possibly replaced by the principle of high stroke volume variation anesthesia which presumes the use of advanced hemodynamic monitoring. KEYWORDS Hepatic resection, central venous pressure, Pringle maneuver, hemodynamics, hemodynamic monitoring, fluid therapy, anesthesia
|
|
|
Magnetic resonance imaging and computational fluid hemodynamics
Jarolímová, Alena ; Švihlová, Helena (advisor) ; Tůma, Karel (referee)
This thesis is focused on study of blood flow through the descending aorta using mag- netic resonance imaging and computational hemodynamics. This combination enables simulations of blood flow in patient specific geometries and under various circumstances such as higher heart rate, velocity or blood pressure. The theoretical part describes the governing equations of the blood flow and possible choices of boundary conditions. The weak formulation and discretization in space and time, which leads to the finite element approximation, is presented. The magnetic resonance data is presented in the second part. The process of segmenta- tion is described together with the preparation of the velocity data for comparison with simulation results. Limitations of magnetic resonance imaging are also presented. The developed methodology is one of the contributions of this thesis. The qualitative and quantitative comparison of simulation results and the magnetic res- onance velocity data is presented in the third part. The main result of the thesis is in the comparison of the flow under different wall boundary conditions. The most important finding is that the best fit for the data is the free-slip wall boundary condition, which is the opposite of commonly used no-slip wall boundary condition. 1
|
|
|
Hemodynamic adaptation mechanisms of heart failure to percutaneous venoarterial extracorporeal circulatory support
Hála, Pavel ; Kittnar, Otomar (advisor) ; Szárszoi, Ondrej (referee) ; Havránek, Štěpán (referee)
Introduction: Venoarterial extracorporeal membrane oxygenation (VA ECMO) is widely used in the treatment of circulatory failure, but repeatedly, its negative effects on the left ventricle (LV) have been observed. The purpose of this study is to assess the influence of ex- tracorporeal blood flow (EBF) on systemic hemodynamic changes and LV performance parameters during VA ECMO therapy of decompensated heart failure. Methods: Porcine models of low-output chronic and acute heart failure were developed by long-term fast cardiac pacing and coronary hypoxemia, respectively. Profound signs of circulatory decompensation were defined by reduced cardiac output and tissue hypoperfusion. Sub- sequently, under total anesthesia and artificial ventilation, VA ECMO was introduced. LV performance and organ specific parameters were recorded at different levels of EBF using an LV pressure-volume loop analysis, arterial flow probes on carotid and subclavian arteries, and transcutaneous probes positioned to measure cerebral and forelimb regional tissue oxygen saturations. Results: Conditions of severely decompensated heart failure led to systemic hypotension, low tissue and mixed venous oxygen saturations, and increase in LV end-diastolic pressure. By increasing the EBF from minimal flow to 5 L/min, we observed a...
|
|
|
Blood flow modeling in arterial stenosis.
Matajová, Adéla ; Hron, Jaroslav (advisor) ; Dolejší, Vít (referee)
Arterial stenosis is a disease characterized by the buildup of a waxy substance inside the artery, which is associated with certain risks. It is difficult to eval- uate the severity of the stenosis, yet the diagnosis can become more accurate using computational fluid dynamics simulations. The present thesis introduces and applies the model of hemodynamics based on the Navier-Stokes equations, implemented in the FEniCS software employing the finite element method. The main focus lies on the prescription of the boundary condition at the outlet of the computational domain. The impact of the outlet boundary condition on medically significant quantities such as the wall shear stress is analyzed in a two- dimensional benchmark case. It appears that the right choice of the boundary condition is fundamental, in particular when vortices occur and propagate across the outlet boundary. The next part of the work is dedicated to the prescrip- tion of the outflow rate in the case of more than one outlet, corresponding to an artery branching inside the computational domain. The physically meaningful flux distribution is derived introducing Murray's law and its extension. Finally, the blood flow is simulated in a three-dimensional geometry of a patient-specific carotid artery. 1
|
|
|
Biventricular pacing optimization by means of the dyssynchrony parameter
Jurák, Pavel ; Leinveber, P. ; Halámek, Josef ; Plešinger, Filip ; Postránecká, T. ; Lipoldová, J. ; Novák, M.
To improve Cardiac Resynchronization Therapy (CRT), different interventricular delay (VVD) settings can be used. However, relatively small VVD induced hemodynamic changes cannot be measured by standard echocardiographic methods. The QRS complex duration (QRSd) is mostly the main criterion. Here we introduce a new dyssynchrony parameter (DYS) that is able to more accurately detect improved electrical synchrony. Methods: 12-lead 5 kHz ECG during 3-10 minute rest period was measured in 46 patients with CRT OFF and CRT ON with VVD 0 ms (CRT0) and -20 ms (CRT20). We detected QRSd and the dyssynchrony parameter DYS as the time difference between 500-1000 Hz averaged envelopes positions in the V1 and V6 leads in the QRS complex region. Results: 32 of 46 patients had a positive CRT response manifested by QRSd shortening and a DYS decrease. 28 of 32 patients had a positive LV pre-excitation effect: additional QRSd shortening of 4.7+/-.9 ms and a DYS decrease of 12.6+/-7.5 ms. The correlation coefficient of QRSd and DYS changes (CRT 0 vs CRT 20) was 0.23 and indicates information diversity. The DYS parameter differs from QRSd and provides a significantly higher response to VVdelay changes (p <; 0.001).
|
|
|
Hemodynamic optimalization in hepatic recection
Zatloukal, Jan ; Pradl, Richard (advisor) ; Cvachovec, Karel (referee) ; Málek, Jiří (referee)
Lowering of central venous pressure in hepatic surgery is nowadays widely recommended and used procedure. Low central venous pressure anesthesia is associated with decreased blood loss and improved clinical outcome. There are several approaches how to reach low central venous pressure. Till now none of them is recommended as superior in terms of patient safety and clinical outcome. Concurrently there is still debate if to use the low central venous pressure anesthesia principle or if it could be replaced with a principle of anesthesia with high stroke volume variation (or another dynamic preload parameter) with the use of a more sophisticated hemodynamic monitoring method. Results of our study didn't show any significant difference between two approaches used for reduction of central venous pressure, but suggest that the principle of low central venous pressure anesthesia could be possibly replaced by the principle of high stroke volume variation anesthesia which presumes the use of advanced hemodynamic monitoring. KEYWORDS Hepatic resection, central venous pressure, Pringle maneuver, hemodynamics, hemodynamic monitoring, fluid therapy, anesthesia
|
|
|
Projection method applied to modelling blood flow in cerebral aneurysm
Hrnčíř, Jakub ; Hron, Jaroslav (advisor) ; Knobloch, Petr (referee)
This thesis is motivated by a problem of cerebral aneurysms, which are abnormal bulges on the arteries which supply blood for our brain. These aneurysms can rupture and cause death or permanent neurological deficits. To study the evolution of aneurysms and assess the risk of rupture, mathematical modelling might be used to compute otherwise unobtainable information about blood flow inside the aneurysm. For this reason it is essential to be able to model blood flow in sufficiently high resolution. A goal of this thesis was to implement standard projection method for the solution of unsteady incompressible Navier-Stokes equations using the free finite element software FEniCS to create a working code adjusted to the need of this particular application. The incremental pressure correction scheme was chosen. Various shortcomings of this method are described and a proper choice of boundary conditions and other implementation issues are discussed. A comparison of computed important hemodynamic indicator wall shear stress using new and previously used solution approach are compared. A test of the new code for parallel efficiency and performance on finer meshes for a real medical case was conducted. Powered by TCPDF (www.tcpdf.org)
|
guest ::
