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Computational modelling of heart contraction
Vaverka, Jiří ; Polzer, Stanislav (referee) ; Burša, Jiří (advisor)
This thesis aims to determine the impact of slowed myocardial conduction velocity and depressed myocyte contractility on the duration of isovolumic contraction time (ICT) of the left ventricle by carrying out simulations using finite element method. A 3D finite element model enabling to simulate both physiological and pathological states of myocardium was created. The model is based on simplified ellipsoidal geometry and accounts for anisotropic behavior of myocardium, its asynchronous contraction and variations in the arrangement of muscle fibers. Slowing of conduction velocity to a half of its physiological value resulted in prolongation of ICT by 27 %; slowing of shortening velocity of myocytes by the same percentage prolonged ICT by 73 %. It is therefore concluded that ICT can be much more prolonged due to depressed contractility than due to conduction slowing. The presented results give an idea of the extent to which ICT can be prolonged due to depressed contractility and conduction slowing and therefore can be useful in identifying the causes of decreased myocardial performance in heart disease.
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Segmentation of Cardiac MR Images
Dohnalová, Petra ; Mézl, Martin (referee) ; Jiřík, Radovan (advisor)
This diploma thesis focuses on the influence of myocardial fibrosis on cardiac activity, changes in end-diastolic and end-systolic volume, as well as changes in ejection fraction. The theoretical part is focused on studying the methods used in left ventricular segmentation. The goal is then to implement an algorithm suitable for left ventricular segmentation on the supplied dataset. Based on segmentation, the effect of myocardial fibrosis on the group of rats with induced fibrosis is monitored, at the same time the data are compared with the control group of healthy rats.
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Expert System for Detection of Ventricular Extrasystoles
Svánovská, Zuzana ; Mézl, Martin (referee) ; Sekora, Jiří (advisor)
Ventricular premature beats are ectopic changes in the ECG signal. Detection of ventricular extrasystoles on 12leads ECG was created in MATLAB. At first my work involves whether the ventricular premature beats comes from the right or the left ventricle. Another algorithm evaluates the incidence outflow tract of the chamber. If the previous algorithm shows signs of indecision, another algorithm is used for detection of ventricular extrasystoles at another location in the left ventricle. The last step is to narrow the area of detection which makes it easier to find the place of origin.
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Analysis of stresses in left ventricular wall during isovolumic contraction
Janoušek, Petr ; Burša, Jiří (referee) ; Vaverka, Jiří (advisor)
The objective of this work is the analysis of stresses in the left heart ventricle during the isovolumic-contraction phase, in which blood is compressed without changing its volume in the ventricle. In this work, the left ventricle is modeled using a simplified axisymmetric sphere in order to be able to (1) perform an analytical solution from the relations given in the literature corresponding to the theory of linear elasticity, and (2) compare this solution with the model calculated by the finite element method. The model itself is a thick-wall sphere, which is affected by an internal overpressure arised as a reaction from the compressed blood. In order to achieve a constant internal volume, an active strain which acts against the internal pressure is also considered.
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Computational study of the impact of disorders in excitation propagation on left ventricular contraction
Vaverka, Jiří ; Rohan,, Eduard (referee) ; Horný, Lukáš (referee) ; Burša, Jiří (advisor)
Tato disertační práce se zabývá výpočtovým modelováním kontrakce levé srdeční komory pomocí metody konečných prvků. Primárním cílem práce je vyhodnotit vliv blokády levého Tawarova raménka na ejekční frakci komory. Dále je vyšetřován dopad blokády na pohyby komory během srdečního cyklu, na lokální hodnoty přetvoření a na rozložení napětí ve stěně. Průběh elektrické aktivace jak zdravé komory, tak i komory s blokádou je modelován pomocí monodoménové rovnice svázané s pseudo-modelem buněčné membrány, který byl navržen za účelem snížení výpočetní náročnosti monodoménové rovnice. Rychlost šíření vzruchu v myokardu je uvažována ortotropní. Vypočítané časové průběhy elektrické aktivace ukazují, že blokáda levého Tawarova raménka prodlužuje dobu depolarizace komory o 50 %, což je v souladu s udávanými délkami trvání QRS komplexu na EKG u zdravých jedinců a u pacientů s blokádou. Průběhy elektrické aktivace jsou následně využity v simulacích kontrakce komory pro předepsání počátku kontrakce jednotlivých prvků sítě. Pasivní mechanická odezva myokardu je v těchto simulacích popsána pomocí ortotropního hyperelastického modelu. Aktivní napětí vyvolané svalovou kontrakcí je do modelu zahrnuto prostřednictvím časově závislého tenzoru aktivního přetvoření. Do počáteční konfigurace modelu, reprezentující stav komory na konci diastoly, je před zahájením kontrakce zahrnuto předpětí odpovídající end-diastolickému tlaku v komoře. Časový průběh komorového tlaku během ejekční fáze je modelován pomocí dvouparametrického modelu Windkessel. Výsledky simulací ukazují, že blokáda levého Tawarova raménka nesnižuje významně čerpací schopnost komory. Predikovaný pokles ejekční frakce v důsledku blokády činí pouze 2,3 %, což je v souladu s některými publikovanými klinickými výsledky. Vypočítané časové průběhy posuvů a přetvoření ve vybraných místech modelu taktéž vykazují některé charakteristiky popisované klinickými nebo experimentálními studiemi. V oblasti mezikomorového septa byly pozorovány výrazně vyšší hodnoty napětí než v ostatních částech komory; tyto výsledky však bude nutné ověřit dalšími výpočty, neboť v současném modelu není septum zatíženo silovými účinky vyvolanými kontrakcí pravé komory.
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Inverse modelling of stresses in deformed configuration of left ventricle
Zajac, Radim ; Hájek, Petr (referee) ; Vaverka, Jiří (advisor)
The bachelor thesis deals with the development of a FEM model of the left ventricle from a freely available stl model obtained from magnetic resonance images and the modification of this model to make it usable for calculation in Ansys MAPDL. The model was defined with isotropic hyperelastic mechanical properties obtained from the actual myocardial properties obtained from tensile tests described in the accompanying literature. A FEM model corresponding to the stress-free state of the left ventricle was obtained and the stress field of the loaded geometry was reconstructed after loading this null geometry. The reconstructed stress field cannot be considered as real due to the idealization of the material and the neglect of the application of pressures on the epicardium of the left ventricle.
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Analysis of stresses in left ventricular wall during isovolumic contraction
Janoušek, Petr ; Burša, Jiří (referee) ; Vaverka, Jiří (advisor)
The objective of this work is the analysis of stresses in the left heart ventricle during the isovolumic-contraction phase, in which blood is compressed without changing its volume in the ventricle. In this work, the left ventricle is modeled using a simplified axisymmetric sphere in order to be able to (1) perform an analytical solution from the relations given in the literature corresponding to the theory of linear elasticity, and (2) compare this solution with the model calculated by the finite element method. The model itself is a thick-wall sphere, which is affected by an internal overpressure arised as a reaction from the compressed blood. In order to achieve a constant internal volume, an active strain which acts against the internal pressure is also considered.
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Segmentation of Cardiac MR Images
Dohnalová, Petra ; Mézl, Martin (referee) ; Jiřík, Radovan (advisor)
This diploma thesis focuses on the influence of myocardial fibrosis on cardiac activity, changes in end-diastolic and end-systolic volume, as well as changes in ejection fraction. The theoretical part is focused on studying the methods used in left ventricular segmentation. The goal is then to implement an algorithm suitable for left ventricular segmentation on the supplied dataset. Based on segmentation, the effect of myocardial fibrosis on the group of rats with induced fibrosis is monitored, at the same time the data are compared with the control group of healthy rats.
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Role of phospholipases A2 in cardioprotection induced by continuous normobaric hypoxia in rat heart
Kyclerová, Eva ; Nováková, Olga (advisor) ; Novotný, Jiří (referee)
Recently, they are examined various means for activating the endogenous signalling pathways leading to increased resistance of the myocardium from ischemic/reperfusion (I/R) injury. One of them is the adaptation to chronic hypoxia, which has been shown to reduce the incidence and severity of ventricular arrhythmias, improves the recovery of postischemic contractile function of the heart and particularly reduces the extent of myocardial infarction. Since the function of the heart depends on the maintenance of membrane integrity of cardiomyocytes there are very important phospholipase A2 (PLA2) which are involved in the repair of cellular membranes. Also they are an important component of the protective signalling pathways because they cleave membrane phospholipids to produce lipid signalling molecules. Elucidate the role of PLA2 and the precise mechanism of action of signalling pathways leading to cardioprotection could be important for the prevention and treatment of cardiovascular diseases. Therefore, in this thesis we examined the influence of continuous normobaric hypoxia (CNH) to the relative representation of cardiac PLA2 (secretory - sPLA2IIA, calcium-independent - iPLA2, cytosolic - cPLA2α and its phosphorylated form - p-cPLA2α), and proteins involved in the activation and phosphorylation of...
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Echocardiographic assessment of left ventricular systolic function in rats adapted to hypoxia and exercise training
Hrdlička, Jaroslav ; Papoušek, František (advisor) ; Vybíral, Stanislav (referee)
- 4 - Abstract Adaptation to hypoxia or exercise training has cardioprotective effects against acute ischemic injury, but can potentially negatively influence heart function. Possible negative changes depend on the degree of hypoxia and exercise training intensity. It is therefore necessary to evaluate the effects of the specific adaptation protocols used. The ideal technique is echocardiography, which enables non-invasive, repeated and long-term measurements of the same individual allowing to study the development of changes in the course of adaptation. The aim of this study was to determine the effects of selected protocols of adaptation to intermittent hypobaric hypoxia (corresponding to the altitude of 4,000 to 8,000 meters above sea level, for 15 weeks in total) and exercise training (running speed 30 m.min-1 for 60 min a day, 4 weeks in total) on the left ventricle geometry and systolic function in rats. We assessed basic echocardiographic parameters of the ventricle geometry and function such as fractional shortening, ejection fraction, stroke volume, cardiac output etc. The adaptation of rats to intermittent hypobaric hypoxia lead neither to the impairment of systolic function nor to the development of left ventricle hypertrophy compared to controls; signs of moderate hypertrophy were observed only...
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