Wyniki wyszukiwania - Biblioteka Nauki

1

Multiscale approach to modelling blood flow

100%

Jakubowicz A. , Pietrzyk M.

Computer Methods in Materials Science

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2013

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tom Vol. 13, No. 4

480--492

EN

The three dimensional multiscale model is introduced for studying of a clot formation in vessel with stenosis. The novel multiscale model based on separation of fluid flow calculation and red blood cells deformation is proposed. The macroscale model for fluid dynamic is described by lattice Bolzmann method (LBM). The deformation of red blood cells is defined by spectrin link method. The interaction between those two methods is handled by immersed boundary method. Simulation results demonstrate the structure of the thrombus for three simple geometries.

PL

W artykule przedstawiony jest trójwymiarowy wieloskalowy model mający na celu modelowanie tworzenia się skrzepu w naczyniu krwionośnym ze zwężeniem. Zaproponowane nowatorskie podejście, oparte jest na rozdzieleniu obliczeń przepływu płynu i odkształceń krwinek czerwonych. Poziom makro przepływu krwi jest obliczony za pomocą metody siatkowej Boltzmann (ang. lattice Boltzmann method). Deformacja krwinek czerwonych opisana jest przez metodę powiązań spektryny (ang. spectrin link method).Interakcje między tymi dwoma metodami są możliwe dzięki metodzie zanurzonej ścianki (ang. immersed boundary method). Wyniki symulacji przedstawiają kształt skrzepu dla trzech prostych geometrii.

2

Influence of emissivity changes on the blood flow rate determined on the basis of heat balance equation

100%

Jasiński M.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

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2010

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tom Vol. 9, nr 1

37-44

EN

The changes of human skin emissivity with regard to the skin and ambient temperature are discussed. The concept of body heat balance equation is used to evaluate of blood flow rate. In order to determine the influence of variations of emissivity on radiative heat transfer and blood flow rate value the direct approach of sensitivity analysis is applied.

3

Non-Newtonian effects in a fluid-structure interaction model for atherosclerosis

100%

El Khatib N. , Genieys S. , Zine A. M. , Volpert V.

Journal of Technical Physics

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2009

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tom Vol. 50, no 1

55-64

EN

The inflammatory process of atherosclerosis leads to the formation of an atheroma plaque in the blood vessel. The interaction between the blood and the plaque may have dangerous consequences such as the rupture of the plaque. This rupture exposes tissue factors to the blood flow, leading to the formation of a clot that might result in a heart attack or an ischemic stroke. The blood-plaque interaction may also produce recirculations downstream of the plaque, and these recirculations enhance the risk of clot formation. In this paper we study the blood-plaque interaction using a fluid-structure interaction model. The atheroma plaque is composed of a lipid pool and a fibrous cap and both are modeled as hyperelastic materials. The blood is supposed to be a non-Newtonian fluid with a variable viscosity modeled by the Carreau law. The parameters used in our simulations are taken from experimental data. We investigate the non-Newtonian effects on the recirculations downstream of the atheroma plaque and on the stress over the plaque. The simulations show that the Newtonian model significantly overestimates the recirculations in comparison with the non-Newtonian model. They also show that the Newtonian model slightly underestimates the stress over the plaque for usual shear rates, but that this underestimation can become significant for low shear rates.

4

Comparative analyses of blood flow through mechanical trileaflet and bileaflet aortic valves

100%

Pawlikowski M. , Nieroda A.

Acta of Bioengineering and Biomechanics

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2022

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tom Vol. 24, no. 2

141--152

EN

The primary aim of the present study was to compare the bileaflet and trileaflet aortic valves’ performance during uniform blood flow model and boundary conditions. The secondary aim of the study was to determine the effect of Newtonian/non-Newtonian fluid flow assumption on blood flow directly behind the trileaflet valve. Methods: The geometrical model of the whole system consist of the left ventricle, fragment of the aorta and mechanical valves. A representation of pulsatile flow was obtained by measuring blood flow velocity (Doppler ultrasound examination). We have assumed turbulent blood flow. We considered two blood models, Newtonian and non-Newtonian (Carreau model). The valves’ performance was assessed using the reduced stress in the valves, the shear stress in the aortic wall, flow velocity field and the effective orifice area. Results: The maximum von Mises stress for the bileaflet valve leaflets was 0.3 MPa and for the trileaflet valve – 0.06 MPa. The maximum flow velocity for the bileaflet valve was 4.52 m/s for 40° and for the trileaflet valve – 5.74 m/s. Higher shear stress was present in the bileaflet (151.5 Pa) than for the trileaflet valve (49.64 Pa). Conclusions: The results indicate that central blood jet for the trileaflet valve contributes to more physiological blood flow and decreases the risk of haemolysis. The central flow minimises the risk of leaflet dislocation. In addition, lower stresses extend the durability of the valve. However, the trileaflet valve geometry has also disadvantages, for instance, small peripheral streams or relatively low effective orifice area.

5

Wyznaczanie względnej i bezwzględnej wartości zmian rezystancji zastępczego krwiobiegu nerki

100%

Muc A. , Matulewicz W. , Retkowski M.

Pomiary Automatyka Kontrola

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2007

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tom R. 53, nr 4

84-86

PL

Zaproponowano sposób wyznaczania bezwzględnych i względnych zmian rezystancji w modelu elektrycznym krwiobiegu nerki. W oparciu o znane analogie między zjawiskami przepływu krwi w naczyniach i organach, a przepływem prądu w obwodach elektrycznych, zastosowano opisaną metodę do wyznaczenia zmian oporu naczyniowego nerki dla rzeczywistych danych medycznych. Przeprowadzono doświadczenie medyczne in vivo, polegające na zarejestrowaniu ciśnienia tętniczego i prędkości krwi w tętnicy nerki przeszczepionej, przed i po wysiłku fizycznym. Bezwzględne i względne zmiany oporu naczyniowego porównano ze zmianami współczynnika RI (indeks oporowy).

EN

The trend analysis of changes in parameters of the electric analogue of the kidney blood circulation will facilitate after transplantation the recognition of the clinical state of the kidney and the easier recognition of potential pathologies will make possible. In research was compared: the resistance index (RI), average value of blood flow in renal artery and the vascular resistance of kidney before and after effort. An equivalent electric circuit of kidney blood vessels was created for analysis of blood flow in the renal artery. An arterial system pressure and a waveform of the blood velocity and RI were recorded in the renal artery with using the ultrasound scanner of Doppler at woman with transplant's kidney. On the base of the calculated amplitude spectrum the parameters of the equivalent electric circuit of the kidney blood circulation were appointed. In conducted research, value RI increased about 8% after effort. After effort the average value of blood flow dropped about 28%, however vascular resistance increase about 54%. The evaluation of state of transplanted kidney on the base the change of vascular resistance is more accurate than appointing RI. The method seems be useful for hemodynamic evaluation and after clinical tests for diagnostic of the transplanted kidney.

6

The Dynamics of Human Central Arterial System

100%

Paszyński M. , Kalita P. , Schaefer R.

Schedae Informaticae

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2005

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tom Vol. 14

35-59

EN

The paper presents mathematical and numerical models of the blood flow in human arteries. We describe selected modelling techniques for the mechanical phenomena occurring in the arteries: blood flow, displacement of the wall and the fluid-structure interaction be-tween the blood and the wall. The paper concentrates on the theoretical results showing the conditions of applicability of presented models. We describe variational models for the Casson flow of blood as well as stochastic Fluid Particle Model (FPM) modified for the nonlinear flows. For the artery wali we describe the model which is the physically nonlinear Koiter shell and the Finite Element Method (FEM). We also present the simulations of the fluid-structure interaction that uses the weakly coupled approach of FPM for blood with FEM for the wall.

7

Numerical simulation of blood flow and cholesterol distribution for middle cerebral artery with coarctation

100%

Naito M. , Mizoguchi K. , Takagi Y. , Okano Y.

Journal of Automation Mobile Robotics and Intelligent Systems

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2009

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tom Vol. 3, No. 4

179-183

EN

In order to understand of coarctation growth mechanism in a blood tube, numerical analysis for blood flow and cholesterol distribution in a blood tube was carried out. Numerical results showed that back flow existed behind the coarctation, and it was found that high blood pressure (HBP), and nonelastic conditions increased the cholesterol concentration behind the coarctation.

8

A short review of blood flow modelling methods: from macro- to microscales

100%

Kaczorowska K. , Tesch K.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2017

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tom Vol. 21, No 1

5--16

EN

The aim of this paper it to review various scale approaches to the blood flow modelling. Blood motion may be described by three types of mathematical models according to the observed scales or resolutions, namely microscopic, mesoscopic and macroscopic descriptions. The above approaches are discussed together with their advantages and disadvantages. Several results of mesoscopic simulations are presented with particular attention paid to mesoscale semi-continuum models suitable for real-time blood flow visualisation.

9

Numerical Analysis of an Influence of a Vertebral Arteries Joint Angle Change on Blood Flow

100%

Jozwik K. , Obidowski D. , Pogorzelski M.

Computer Methods in Materials Science

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2009

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tom Vol. 9, No. 1

72-78

EN

Cerebral circulation can be regarded as the most important element of blood circulation. Total ischemia of neurotic cells, lasting longer than a few minutes, is irreversible in its consequences and results in their death. Due to that fact, blood must constantly be delivered to this region of human body. The primary system of brain blood supply consists of independent systems of two carotid and vertebral arteries. Vertebral arteries join into a basilar artery. This joint has a specific character as only 2% of all nodes are vessel joints. Moreover, due to its spatial shape, various diameters of inner vessels, various lengths as well as various joint angles, becomes an area of interesting research. Because of a lack of opportunity in direct diagnosis of this area, numerical experiments on average combinations of geometric models have been carried out. To carry out these investigations two 3D models of artery system differing in the value of a joint angle of vertebral arteries and basilar artery, starting with the aortic ostium and finishing with the basilar artery have been generated. At the inlet to the system three different velocities of the liquid modeling blood have been applied one by one. The results of the simulation indicate the way the joint angle and velocity change at the inlet influences the character and velocity of the flow in the area under analysis. Also, they clearly show which angle would be better from the view point of the flow haemodynamics.

PL

Krążenie mózgowe można uznać za najważniejszy element krążenia krwi. Całkowite niedokrwienie komórek nerwowych trwające dłużej niż kilka minut jest nieodwracalne w skutkach i powoduje ich obumieranie. W związku z tym, krew musi być nieustannie dostarczana do tego regionu ludzkiego ciała. W skład głównego systemu zasilania mózgu w krew wchodzą niezależne układy dwóch tętnic szyjnych oraz kręgowych. Tętnice kręgowe łączą się tworząc tętnicę podstawną. Zespolenie ma osobliwy charakter, gdyż tylko 2% wszystkich węzłów naczyniowych stanowią połączenia naczyń. Ponadto, ze względu na przestrzenny kształt, różne średnice wewnętrzne i różne ich długości jak również różne kąty zespolenia stanowi ono interesujący obszar badań. Ze względu na brak bezpośredniej możliwości diagnostyki tego obszaru, przeprowadzono badania numeryczne na uśrednionych wariantach geometrycznych modelu. Do ich przeprowadzenia zostały wygenenrowane dwa modele 3D układu tętnic, różniących się wartością kąta zespolenia tętnic kręgowych w tętnicę podstawną, począwszy od aorty, kończąc na tętnicy podstawnej. Na wlocie do układu zadawane były kolejno trzy różne prędkości płynącego czynnika modulującego krew. Uzyskane wyniki symulacji pokazały jak zmiana kąta zespolenia i prędkości na wlocie wpływa na charakter i prędkość przepływu w badanym rejonie, który kąt byłby lepszy ze względu na hemodynamikę przypływu.

10

Mathematical model for a Herschel-Bulkley fluid flow in an elastic tube

88%

Vajravelu K. , Sreenadh S. , Devaki P. , Prasad K.

Open Physics

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2011

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tom 9

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nr 5

1357-1365

EN

The constitution of blood demands a yield stress fluid model, and among the available yield stress fluid models for blood flow, the Herschel-Bulkley model is preferred (because Bingham, Power-law and Newtonian models are its special cases). The Herschel-Bulkley fluid model has two parameters, namely the yield stress and the power law index. The expressions for velocity, plug flow velocity, wall shear stress, and the flux flow rate are derived. The flux is determined as a function of inlet, outlet and external pressures, yield stress, and the elastic property of the tube. Further when the power-law index n = 1 and the yield stress τ 0 → 0, our results agree well with those of Rubinow and Keller [J. Theor. Biol. 35, 299 (1972)]. Furthermore, it is observed that, the yield stress and the elastic parameters (t 1 and t 2) have strong effects on the flux of the non-Newtonian fluid flow in the elastic tube. The results obtained for the flow characteristics reveal many interesting behaviors that warrant further study on the non-Newtonian fluid flow phenomena, especially the shear-thinning phenomena. Shear thinning reduces the wall shear stress.

11

Effects of substance P on intestinal circulation and oxygen consumption

88%

Pawlik W. W. , Gustaw P. , Czarnobilski K. , Sendur R. , Konturek S. J.

Acta Physiologica Polonica

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1987

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tom 38

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nr 5

12

Finite element analysis of the hemodynamics in the human carotid artery bifurcation

88%

Postelnicu A. , Minea D.

Applied Mechanics and Engineering

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2000

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tom Vol. 5, no 4

759-772

EN

The present paper brings new lights on blood flow patterns in rigid artery bifurcation models, differing in angle of bifurcation. Using the ANSYS 5.4/FLOTRAN package, a numerical analysis in two dimensions was performed, under physiologically relevant flow conditions. For two bifurcation models, one with large angle the other with a small one, the distributions of velocities, shear-stress and pressure in the domain of carotid artery bifurcation have been obtained. It is argued and proved that the vascular geometry at the bifurcation level represents a risk factor in atherogenesis, the relevant factors for this process being the flow separation, reversal flow regions and wall shear stress.

13

Numerical Study of a Flow in the Cerebral Arterial Circle

88%

Obidowski D. , Jozwik K. , Reorowicz P.

Computer Methods in Materials Science

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2009

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tom Vol. 9, No. 1

79-84

EN

Blood is supplied to the brain by two internal carotid and two vertebral arteries. These arteries join to form the cerebral arterial circle (also called the Circle of Willis or CoW). This unique arrangement of human vessels ensures blood supply to the brain despite of any pathology in the geometry of arteries supplying the brain. Computed Tomography was used in this case for imagining the CoW as well as the arteries supplying it. The images obtained during the test were used to develop numerical model of one particular patient?s vessels geometry. Finally, with the use of numerical methods it is possible to simulate a realistic flow within the region where no other method can be used and thus one can analyze an influence of the pathological narrowing onto the cerebral perfusion. Using Computed Tomography large series of two-dimensional X-ray images were taken along the patient's axis during one test. The distance between single images is 0.6 mm. Vessels as they are soft tissues have to be visualized by contrast. Having these images, a three-dimensional path of the single artery was studied and its geometry was generated in CAD software (SolidWorks). Then, 3D mesh was generated using CFX Mesh code. Numerical experiment was carried out for different velocities within the physiological range. Blood was modeled as a Newtonian fluid.

PL

Głównymi tętnicami dostarczającymi krew do mózgu są dwie tętnice szyjne wewnętrzne oraz dwie tętnice kręgowe. Naczynia te łączą się w jamie czaszki tworząc koło tętnicze mózgu (koło Willisa). Układ ten ma za zadanie zapewnienie prawidłowego ukrwienia mózgu bez względu na zmiany patologiczne w geometrii naczyń zasilających mózg. W pracy tej posłużono się komputerową tomografią,jako sposobem obrazowania naczyń krwionośnych. Zastosowanie obrazów z TK pozwoliło na zbudowanie modelu numerycznego koła Willisa dla indywidualnego przypadku danego pacjenta. W chwili obecnej posługując się metodami numerycznymi możliwe jest odtworzenie rzeczywistego przepływu w obszarze, jak i zbadać wpływ anomalii w budowie na ukrwienie mózgu. Podstawą do zbudowania modelu były serie obrazów pozyskanych w czasie badania badania z wykorzystaniem tomografii komputerowej. W metodzie tej generowany jest obraz 2D na płaszczyznach prostopadłych do głównej osi pacjenta. Płaszczyzny oddalone są od siebie o 0,6 [mm]. Dla uwidocznienia naczyń krwionośnych, które są tkanką miękką, dodano środka kontrastowego. Na podstawie tych obrazów odwzorowano trójwymiarową ścieżkę osi każdego z kanałów. Kolejnym etapem było przeniesienie danych do programu SolidWorks. Następnie wygenerowana została siatka przestrzenna, do wykonania której wykorzystano oprogramowanie CFX Mesh. Symulacje przeprowadzone zostały dla różnych charakterystycznych wartości prędkości z zakresu prędkości fizjologicznych występujących w układzie krwionośnym. Krew została zdefiniowana jako ciecz Newtonowska.

14

Central control of heart rate changes during visual affective processing as revealed by fMRI

88%

Kuniecki M. , Urbanik A. , Sobiecka B. , Kozub J. , Binder M.

Acta Neurobiologiae Experimentalis

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2003

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tom 63

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nr 1

15

Two-phase flow in a catheterized artery with atherosclerosis

75%

Ledesma J. M. , Riahi D. N. , Roy R.

Journal of Theoretical and Applied Mechanics

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2013

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tom Vol. 51 nr 2

409--418

EN

We consider the problem of blood flow in a catheterized artery and in the presence of atherosclerosis, which is chosen based on the available experimental data. The atherosclerosis is a condition where an artery wall thickens as a result of fatty materials such as cholesterol. The use of catheter is of immense importance as a standard tool for diagnosis and treatment in a patience whose artery is affected adversely by the presence of atherosclerosis within the artery. The blood flow in the arterial tube is represented by a two-phase model composing a suspension of erythrocytes (red cells) in plasma. The coupled differential equations for both fluid (plasma) and particles (red cells) are solved theoretically subjected to reasonable modeling and approximations. The important quantities such as plasma speed, velocity of red cells, blood pressure force, impedance (blood flow resistance) and the wall shear stress are computed for different values of the catheter size, axial location of atherosclerosis and the hematocrit due to the red cells-plasma combination of the blood flow system.

PL

W pracy omówiono problem przepływu krwi w tętnicy po zabiegu koronarografii w obecności zmian miażdżycowych, opierając się na osiągalnych danych z badań klinicznych. Miażdżycą nazywamy stan, w którym ściana tętnicy pogrubia się do wewnątrz wskutek odkładania się tłuszczy, głownie cholesterolu. W standardowej metodzie leczenia miażdżycy stosuje się zabieg koronarografii polegający na wprowadzeniu cewnika do upośledzonej tętnicy. W pracy opisano przepływ krwi w przekroju tętnicy za pomocą dwufazowego modelu odzwierciedlającego zawiesinę czerwonych ciałek krwi w osoczu. Sprzężone, różniczkowe równania przepływu płynu (osocza) i ruchu cząstek (czerwonych ciałek) rozwiązano analitycznie w stopniu akceptowalnie przybliżonym. Tak istotne wielkości, jak prędkość przepływu osocza, prędkość czerwonych ciałek, ciśnienie krwi, impedancja (opory przepływu) oraz naprężenia ścinające w ścianie tętnicy obliczono dla rożnych rozmiarów cewnika, osiowego rozkładu złogów miażdżycowych oraz hematokrytu wywołanego dwufazową kombinacją czerwone ciałka-osocze w badanym układzie krwionośnym.

16

Modelling of hemodynamics in 3D bypass models

75%

Vimmr J. , Jonasova A.

Modelling and Optimization of Physical Systems

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2010

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tom z. 9

87--92

EN

The study is divided into two parts. The first one deals with the modelling of non-Newtonian effects in occluded femoral bypass considering steady blood flow. The second part is devoted to the analysis of pulsatile Newtonian blood flow in stenosed coronary bypass applying realistic inlet flow rates. The bypass models are assumed to be idealized and complete, i.e. the native artery and the bypass graft are modelled as tubes with both proximal and distal parts. The governing equations are solved numerically with explicit and implicit schemes formulated in the sense of the finite volume method using developed in-house software.

CS

Tato studie je rozdělena na dvě části. První se zabývá modelováním nenewtonských efektů ve femorálním bypassu pří uvažováni ustáleného proudění krve. Druhá část je věnována analýze pulzujícího proudění krve jakožto newtonské kapaliny v koronárním bypassu. Matematický model je řešen pomocí explicitních a implicitních schémat formulovaných ve smyslu metody konečných objemů a za použití vlastního vyvinutého softwaru.

17

On approach to the modeling process of the blood flow in vessels

75%

Hotra O. , P’yanylo Y.

Metody Informatyki Stosowanej

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2010

|

tom nr 1 (22)

31-41

EN

This paper presents an extended mathematical model of the process of blood flow in vessels taking into account the gravitational force, the trajectory of the flow (in curvilinear vessels), and the hydraulic resistance of the vessel. The influence of these factors on the blood pressure distribution along the vessel was examined. The steady blood flow characterized by average values of pressure, density, and flow rate of blood was considered. The results of computational experiment were compared with corresponding results obtained from the models known in literature.

18

Effects of gadolinium chloride on basal flow and compression-induced rapid hyperemia in the rabbit masseter muscle

75%

Turturici M. , Roatta S.

Journal of Physiology and Pharmacology

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2014

|

tom 65

|

nr 3

19

Viscoelastic changes in the blood and vascular wall in a pulsating circular flow

75%

Beraia M. , Todua F. , Khomeriki I.

Polish Journal of Medical Physics And Engineering

|

2010

|

tom 16

|

nr 1

43-53

EN

Altered flow conditions, such as separation and recirculationg zones, low and oscillatory shear stress, play an important role in the development of arterial disease. Endothelial denudation by the blood flow is the first step in atherosclerosis. The description of blood flow in vivo is complicated due to the viscoelasticity of vessel walls. However, conventional researches of the effect of the blood vessel viscoelasticity on the blood pressure wave propagation using non-linear one-dimensional models do not take into account the viscoelasticity, despite it being importance in the analysis of pulse wave propagation in arteries.The purpose of this paper is to study the impact of the arterial pulse wave on the viscoelastic blood flow and initial factors of atherosclerosis.In 12 healthy men (25-39 years of age) peak velocity, mean velocity, mean flow and net flow in the aorta have been investigated by MR angiography.Initial velocity was registered after 43msec of the ECG-R wave, and it differed from zero at all sites of the aorta, although net flow was equal to zero. Womersley's number from the ascending to the thoracic aorta decreased from 12.5 ± 1.5 to 7.3 ± 1.2; flow modified from inertio-elastic to viscous. Pulse pressure wave move on artery walls fifteen or more times more rapidly than the blood flow. In the aortic arch in protodiastole blood flow separated into the opposite directed streams resulting in wave superposition with the high net flow. At the isthmus area separated waves interferences and reflects to anterograde direction.Pulse oscillation increases strain rate to the contiguous vessel wall flow layers. At the sites with the flow wave negative interference vessel pulse oscillation attenuates and at the boundary reflection flow wave can shift the vessel wall.

20

Simulations of the blood flow in the arterio-venous fistula for haemodialysis

75%

Jodko D. , Obidowski D. , Reorowicz P. , Jóźwik K.

Acta of Bioengineering and Biomechanics

|

2014

|

tom Vol. 16, no. 1

69--74

EN

The Ciminio-Brescia arterio-venous fistula is a preferred vascular access for haemodialysis, but it is often associated with the development of vascular complications, due to changes in hemodynamic conditions. Computational fluid dynamics methods were involved to carry out seven simulations of the blood flow through the fistula for the patient specific (geometrical) case and various boundary conditions. The geometrical data, obtained from the angio-computed tomography, were used to create a 3-dimensional CAD model of the fistula. The blood flow patterns, blood velocity and the wall shear stress, thought to play a key role in the development of typical complications (stenoses, thromboses, aneurysms, etc.), have been analyzed in this study. The blood flow is reversed locally downstream the anastomosis (where the artery is connected to the vein) and downstream the stenosis in the cannulated vein. Blood velocity reaches abnormal value in the anastomosis during the systolic phase of the cardiac cycle (2.66 m/s). The wall shear stress changes in this place during a single cycle of the heart operation from 27.9 to 71.3 Pa (average 41.5 Pa). The results are compared with data found in the literature.