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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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Tribologické metody testování materiálů umělých kloubních náhrad
Pražák, Josef ; Chlup, Hynek ; Franta, L.
In order to achieve a high functional quality of the total artificial joints (TAJ), a special attention must be paid to the selection of suitable materials for the construction (Dumbleton; 1981, O´Kelly; 1979). Nowadays, it seems that the metal parts of the assembly (femoral part for the knee joint) do not pose any problem, but problems of the “soft” parts (tibial part) persist. A careful tribologic testing of considered materials is necessary, consequently. On the other hand, a relevant tribologic testing in a conventional way is extremely time-consuming (a simulation of a 5 km/day for 10 years activity represents a 150 day test approx.). The application of an accelerated testing method is desirable, therefore. Such a method consisting of an application of a special experimental set-up and of an optical evaluation was developed. It was used for a study concerning the lubrication of artificial joints (Pražák; 2000).
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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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