Wyniki wyszukiwania - Biblioteka Nauki

1

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

100%

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

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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.

2

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

100%

Jasiński M.

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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.

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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

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

88%

Postelnicu A. , Minea D.

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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.

5

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.

6

Laser speckle contrast imaging for measuring blood flow

75%

Briers J. D.

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2007

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tom Vol. 37, nr 1-2

139-152

EN

When a diffuse object is illuminated with laser light, a random interference effect known as a speckle pattern is produced. If there is movement in the object, the speckles fluctuate in intensity. These fluctuations can be used to provide information about the movement. A simple way of accessing this information is to image the speckle pattern - the fluctuations cause a blurring of the speckle, leading to a reduction in the local speckle contrast. Thus velocity distributions are coded as speckle contrast variations. The same information can be obtained by using the Doppler effect, but producing a two-dimensional Doppler map requires scanning: speckle imaging provides the same information without the need to scan. This paper reviews the development of laser speckle imaging, starting with the connection established between speckle fluctuations and movement in the nineteen-seventies. In the eighties, a photographic technique for monitoring retinal blood flow was developed, and ten years later a digital version was used to monitor capillary blood flow in the skin. Today, many groups around the world are either using or researching the technique, and the paper will close by presenting some of their recent results.

7

The influence of high tone power therapy on the peripheral microcirculation in the lower limbs

75%

Nowakowska I. , Szymańska J. , Witkoś J. , Wodarska M. , Kucharzewski M. , Dembkowski M.

Physiotherapy

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2009

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tom 17

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nr 4

10-18

PL

Jedną z najnowszych metod wspomagania leczenia wielu schorzeń jest terapia energotonowa. Jest ona nowoczesnym sposobem terapii, powstałym na bazie badań naukowych na polu różnych dziedzin: medycyny, fizyki, matematyki, fizjologii, biochemii i innych. Dzięki tak rozległej płaszczyźnie badań nad High Tone Power Therapy (HiToP) można mówić o niej jako o zjawisku interdyscyplinarnym. Celem pracy była ocena wpływu terapii energotonowej na mikrokrążenie obwodowe kończyn dolnych. Materiał i metoda: badaniami objęto grupę 30 osób w wieku od 20 do 60 lat. W pierwszej podgrupie znalazły się osoby leczone z powodu chorób naczyń obwodowych w zakresie tętniczym i żylnym kończyn dolnych, odpowiednio 4 i 12 osób, a w drugiej osoby zdrowe (14 osób). Wszystkim badanym wykonano serię 10 zabiegów terapii energotonowej w okolicy kończyn dolnych stosując metodę SimulFAMx. Bezpośrednio przed, jak i po serii zabiegów dokonano pomiaru przepływu krwi metodą Laser-Doppler. Wyniki: u wszystkich badanych po wykonanych zabiegach zaobserwowano zwiększenie dynamiki przepływu w mikrokrążeniu obwodowym kończyn dolnych. Wyniki te wykazały pewne zróżnicowanie, aczkolwiek nie całkiem jednoznacznie. Pod wpływem zabiegów stwierdzono wyraźny wzrost przepływu u osób leczonych z powodu zaburzeń naczyniowych, w porównaniu do osób zdrowych, u których zanotowano znaczny wzrost tylko wartości minimalnych. Wnioski: wstępne wyniki wskazują, że terapia energotonowa może być cenną pomocą w leczeniu zaburzeń obwodowego krążenia krwi.

EN

One of the basic diagnostic methods of evaluating the microcirculation vessels is the Laser-Doppler examination which makes it possible to determine the dynamics of the flow and to evaluate the level of blood supply. Among the newest methods of adjunct treatment for various diseases is energotonic therapy which is a modern therapy based on researches carried out in various fields of science: medicine, physics, mathematics, physiology, biochemistry and other. Due to such a wide range of research fields the high tone power therapy may be said to be an interdisciplinary phenomenon. The aim of the research was to evaluate the effects of the high tone power therapy on peripheral microcirculation in the lower limbs. Material and Methods: the research group consisted of 30 people aged from 20 to 60 which was divided into two subgroups. The first subgroup included 16 people treated for peripheral vascular disease in the area of arteries and veins of the lower limbs - 4 and 12 people respectively - and the second subgroup included 14 healthy people. All the examined were undergone a series of 10 procedures of energotonic therapy in the lower limbs by means of the SimulFAMx method. In all the examined before and after the therapy the blood flow was measured using the Laser-Doppler method. Results: an increase in the dynamics of the blood flow in peripheral microcirculation in the lower limbs was observed in all the examined. The results showed certain diversification, yet it was not entirely clear. After the therapy there was a significant increase of the blood flow in patients treated for vascular disorders in comparison with the group of healthy people in which only the minimal values increased significantly. Conclusions: initial results indicate that the high tone energy therapy may be a valuable aid in treating disorders of the peripheral blood circulation.

8

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

75%

Hotra O. , P’yanylo Y.

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2010

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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.

9

Experimental analysis of steady and pulsating flows in collapsible walls

75%

Zbiciński I.

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2007

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tom Vol. 28, z. 3

539-546

EN

An experimental set-up to measure the changes of geometry of elastic walls and input and output pressures for constant and pulsating flow reflecting blood flow in human arteries was designed, built and tested. The paper presents the results of extensive experiments of static and pulsating flow parameters as functions of flow rates and pulsation frequencies for various properties of tested tubes. Aperiodic time series of pressure due to occurrence of turbulent flow have been observed.

PL

Przedstawiono wyniki badań eksperymentalnych przepływu statycznego i pulsacyjnego w elastycznych ściankach odwzorowującego przepływ w naczyniach krwionośnych. Zaprojektowano, zbudowano i przetestowano aparaturę umożliwiającą pomiar on-line zmian średnicy badanej rurki wykonanej z elastycznego materiału i ciśnień dynamicznych przed i za badaną próbką w zależności od natężenia prze-pływu i częstotliwości pulsacji. Zaobserwowano m.in. aperiodyczne zależności czasowe ciśnienia i średnicy rurki wynikające z burzliwego charakteru przepływu płynu.

10

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

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2010

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tom 16

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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.

11

Mathematical analysis of the flow over endothelial glycocalyx

63%

Arslan N.

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2007

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tom Vol. 12, no 4

1165-1171

EN

Mathematical modeling of the flow over the glycocalyx located on the endothelial cells (EC) was investigated. Flow regions are considered as a core flow region which is the flow in the lumen of the vessel which are simiIar flow to the Poiseuille flow inside the straight pipe and the flow over the glycocalyx located on the EC which are considered as flow through the porous media. Solutions were found in both regions and also wall shear stresses (WSS) and drag forces were calculated.

12

Verification of fluid structure interaction model of flow in human arteries

63%

Petera J.

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2007

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tom Vol. 28, z. 3

547-557

EN

An original method was designed to estimate rheological parameters in the situation when an extensive rheological examination of a material is not possible. Particularly, the approach is intended to be used in the examination of blood flow patterns in human vascular system allegedly leading to aneurysm disease. The approach belongs to a class called fluid-structure interaction (FSI) and requires consecutive application of CFD, CSD and CMD. Good agreement was achieved between simulation and experimental results obtained from a specially designed set-up.

PL

Zaprojektowano nową metodę wykorzystującą tzw. analizę odwrotną do oceny parametrów reologicznych materiałów, których wszechstronne badania reologiczne są niemożliwe. Powszechnie uważa się, że zjawiska hydrodynamiczne prowadzą do choroby zwanej anewryzmem. Zaproponowane podejście zostanie więc wykorzystane do badania przepływów krwi w układzie krążenia człowieka. Podejście to należy do klasy oddziaływań płyn-struktura (FSI) i wymaga konsekwentnego zastosowania podejść CFD, CSD i CMD. Zaobserwowano dobrą zgodność między wynikami symulacji i wynikami eksperymentalnymi uzyskanymi za pomocą specjalnie zaprojektowanego stanowiska doświadczalnego.

13

Effects of treadmill training on walking distance and lower limb blood flow in patients with intermittent claudication

63%

Mika P. , Cencora A.

Medical Rehabilitation

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2005

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tom 9(1)

3-9

PL

Cel: U pacjentów z chromaniem przestankowym regularnie prowadzony trening marszowy na bieżni prowadzi do wzrostu dystansu marszu. Mechanizm tej poprawy jest wieloczynnikowy a jedną z prawdopodobnych przyczyn może być wzrost przepływu tętniczego w kończynach dolnych. Przedmiotem badań była ocena zmian dystansu marszu oraz przepływu tętniczego w kończynach dolnych podczas treningu marszowego na bieżni u pacjentów z chromaniem przestankowym. Metoda: 80 pacjentów z miażdżycą zarostową kończyn dolnych (II stopień według Fontaine) było randomizowanych do programu treningowego lub do grupy kontrolnej. Pacjenci z grupy badawczej przez okres 3 miesięcy uczestniczyli 3 razy tygodniowo w treningu marszowym. Sesje składały się z wysiłków marszowych powtarzanych 3-krotnie, każdy o dystansie marszu wynoszącym 85% indywidualnie określonego dystansu chromania. Przed rozpoczęciem programu i po jego zakończeniu w obu grupach oceniano dystans pojawienia się chromania oraz zmiany w prędkości przepływu tętniczego w kończynach dolnych (pomiar indeksu pulsacji metodą dopplerowską). Wyniki: Po 12 tygodniach programu w grupie badawczej zaobserwowano wzrost indeksu pulsacji mierzony na tętnicy podkolanowej (43%), piszczelowej tylnej (59%) i grzbietowej stopy (78,8%). W grupie kontrolnej niewielki wzrost (11,4%) odnotowano na tętnicy podkolanowej. Towarzyszyła temu poprawa dystansu pojawienia się chromania – 119,6% w grupie badawczej i 16,9% w grupie kontrolnej. Zmiany były istotne statystycznie (p< 0,05). Wnioski: Wyniki badań wskazują, że trening marszowy prowadzony u pacjentów z chromaniem przestankowym prowadzi do korzystnych zmian przepływu tętniczego w kończynach dolnych w zakresie poprawy jego prędkości oraz znacznej poprawy dystansu marszu pokonywanego bez bólu.

EN

Background: In patients with intermittent claudication treadmill training improves their walking ability. While the benefits of an exercise rehabilitation programme are recognized, the mechanisms involved are not completely appreciated. The improvement in lower limb blood flow may by one of the mechanisms leading to the increase in walking distance. In the present study arterial blood flow in lower limb as well as walking distance were assessed before and after supervised pain-free treadmill training. Methods: Eighty patients with peripheral arterial occlusive disease (stage II according to Fontaine) were randomised into the treadmill program or to the control group. Patients in the exercising group participated for 3 months 3 times a week in supervised treadmill trainings. Each session consisted of 3 cycles, each amounting to 85% of the pain-free walking distance. Changes in arterial blood flow and the onset of claudication pain were assessed in both groups.Results: After 12 weeks of the treadmill training lower limb blood flow in exercising group significantly improved (p<0.05). Painfree walking distance was prolonged by 119,6% in the exercising group and only 16.9% in the control group. Those changes were statistically significant in both groups (p<0.05).Conclusion: The results indicate that exercise training program using intermittent walking to 85% of the onset of claudication pain leads to a significant improvement in lower limb blood velocity and increase in pain-free walking distance.

14

Herschel - Bulkley model for two-phase blood flow in narrow vessel

51%

Das S. , Saha G. C.

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2010

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tom Vol. 15, no 1

19-34

EN

A mathematical model for a two-phase blood flow through a circular narrow vessel has been developed by considering blood to be a non-Newtonian liquid of Herschel-Bulkley type and taking into consideration the slip velocity at the wall of the vessel. Analytical expressions for velocities of blood in the peripheral layer and central core layer, flow rate and apparent fluidity of blood have been obtained and their natures are portrayed graphically for different parameters.