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Konstitutivní modelování tepenné stěny
Horný, L. ; Chlup, Hynek ; Adámek, T. ; Zitny, R. ; Macková, H.
Inflation tests and uni–axial extension tests of arterial tissue were performed. Experimental data were used in nonlinear regression analysis to identify material model. Arterial tissue was assumed to be incompressible hyperelastic material. 5–parameter strain energy density function based on combination of isotropic Neo–Hookean expression and Fung–type orthotropic expression was used. Computational model for material parameters identification was based on thick–wall tube with axial pre–strains. Residual strains were included. Internal structure of arterial wall was not considered. Fitted material models correspond to experimental data very well.
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Optimalizace měření rychlosti pulzní vlny v tepnách
Macková, H. ; Chlup, Hynek ; Hulan, M. ; Žitný, R.
Measurements of the pulse wave velocity (PWV) in human arteries are important for two different reasons: an early diagnostics of atherosclerosis and identification of material properties of the vessel wall for numerical simulations. The PWV in blood vessels is not constant and classical methods of pressure wave shift between two points are not sufficient. We consider three methods: optical measurements of vessel wall displacement in several points by high speed camera, continual optical measurements of vessel wall displacement by correlator Q-450 and measurements of flow rate and displacements by ultrasonic device. The first method can determine the PWV only between several points. The second method can show 3D reconstruction of displacements with very good resolution. The ultrasound measurements need combination of Doppler ultrasound velocimetry and B-scan imagining. However, the common devices used in medicine do not have any data output. It causes bad resolution.
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Elastic tubes in the mode of self-excited oscillation
Chlup, Hynek ; Maršík, František ; Konvičková, S.
Our paper studies experimentally the self-excited oscillations of thin-walled elastic tubes with respect to the Korotkoff sounds. The self-excited oscillation is a phenomenon, when an elastic tube looses stability of its shape and starts to oscillate, loaded only by continual flow, therefore without any external excitation. The mean flow rates, pressures at the ends of the tube, external pressures and photographs of the shape in two planes were recorded under various modes of oscillation. The effective cross-section and Young’s modulus of the tube wall were calculated by simplified formulas. The data analysis showed an increase of the oscillation frequency with a decrease of the tube wall compliance. It means the frequency of the oscillation is dependent on ratio of the wall thickness and the tube diameter. The mode of the oscillation is also influenced by the transmural pressure. The influence of the axial pretension of the tube is being studied now.
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Self-excited oscillation of the thin-walled elastic tubes
Chlup, Hynek ; Maršík, František ; Konvičková, S.
The simulation of the fluid flow through elastic pipes has many applications in a blood flow through human vessels – investigation of such phenomena as an atherosclerosis generation in artery walls, the Korotkoff's sounds generation or modeling of vascular mechanical substitutes (the so called "stents") and is therefore widely studied. Aim task is to solve the blood flow through the elastic tubes analytically, numerically and experimentally and to analyze the relation of the mechanical properties of the blood and of the vessel wall and flow instabilities, all focused on biomechanics of the cardio-vascular system. The analysis shows that frequency of self-excited oscillations increases with the decrease of arterial compliance.
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Experimentální měření pulzní vlny v elastické trubici
Chlup, Hynek ; Macková, H. ; Žitný, R. ; Konvičková, S.
The pulse wave velocity (PWV) in blood vessels is one of the important hemodynamical parameters for detection of artery health condition. In our laboratory, the PWV in elastic tubes and arteries is measured in vitro. The method is based on optical measurements of displacement of the pulsating tube wall. A high frame rate camera was used. The obtained data were evaluated by several methods and compared. The measured pulse wave velocities were in the same order of magnitude as values based on theoretical calculations and published physiological data.
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Zbytková deformace v bifurkaci lidské aorty
Adámek, T. ; Horný, L. ; Chlup, Hynek ; Franta, L.
At the present paper we report values of opening angles in human aortic bifurcations. A standard method of opening angle measurement was used. Three aortas were measured. Ten samples were excised from each aorta. Three rings were obtained from abdominal aorta close to the bifurcation, arteria iliaca communis dextra and sinistra and one form the bifurcation. The last one was composed of two rings, left and rignt, which were measured together. The residual strains were occurred in human aortic bifurcations and had different values in the left and the right branch of the bifurcated artery. The results of at the bifurcation can be influenced by fact that the branches of iliac arteries are still intergrown here. Two kinds of the opening angle investigation at the bifurcation were tested, a bifurcation septum fixed method and a circular sector fixed method. But both revealed differences in the opening angle values at the bifurcation.
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Samobuzené oscilace elastické trubice
Chlup, Hynek ; Macková, H. ; Maršík, František ; Konvičková, S.
Our paper studies experimentally the self-excited oscillations of thin-walled elastic tubes with respect to the Korotkoff sounds. The self-excited oscillation is a phenomenon, when an elastic tube looses stability of its shape and starts to oscillate, loaded only by continual flow, therefore without any external excitation. An experimental set-up was designed for the experiments. The mean flow rates, pressures at the ends of the tube and external pressures were recorded under various modes of oscillation. The effective cross-section and elastic modulus of the tube were calculated by simplified formulas. The data analysis showed an increase of the oscillation frequency with a decrease of the tube wall compliance. It means the frequency of the oscillation is dependent on ratio of the wall thickness and the tube diameter. The mode of the oscillation is also influenced by the transmural pressure.
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Fyzikální model systémového odporu krevního řečiště člověka
Chlup, Hynek ; Konvičková, S.
The element simulating the body tissue resistance changes represents the dominant part in the cardiovascular modeling circuit set-ups. The element simulating the distal resistance of system circuit of the bloodstream systemic resistance was created. The total resistance of this apparatus is possible to change with connecting proper number of resistance segments, in dependence of experiments. The element is made up of multiple embranchment flow liquids and resistance segments. The flow cross-section will be extended fivefold from input to output by full opening of SO.
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