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Numerical simulations of the pulsatile blood flow in the different types of arterial fenestrations: Comparable analysis of multiple vascular geometries

Tyfa Z., Obidowski D., Reorowicz P., Stefańczyk L., Fortuniak J., Jóźwik K.

Biocybernetics and Biomedical Engineering

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2018

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Vol. 38, no. 2

228--242

EN

In medical terms, fenestration stands for an anomaly within the circulatory system in which the blood vessel lumen is divided into two separate channels that rejoin in the distal part of this vessel. The primary objective of this research was to analyze the impact of the left vertebral artery (LVA) and basilar artery (BA) fenestrations on the blood flow characteristics in their regions and downstream, in the cerebral circulation. The geometrical data, obtained from the angio-Computed Tomography, were the basis for the generation of a 3D model in SolidWorks 2015. In order to observe the flow characteristics within the whole spatial domain, computational fluid dynamics was involved in performing simulations of the blood flow in the patient-specific arterial system (beginning with the aortic arch and finishing with the Circle of Willis). To examine the flow distribution changes resulting from altered fenestration geometries, additional models were built. The blood flow velocity, volume flow rate and shear stress distribution were analyzed within this study. It was proven that the length/size/ position of the fenestration altered the flow characteristics in different manners. The investigations showed that the patient-specific LVA, at the V3 section (extracranial part of the artery located between the spine and the skull), is not a reason of aneurysm formation. However, BA fenestration at the proximal segment might be a possible reason of future aneurysm formation. It was proven that the computational fluid dynamics tool could support medical diagnostic procedures and multivessel brain vascular disease treatment planning.

2

Blood flows in end-to-end arteriovenous fistulas: Unsteady and steady state numerical investigations of three patient-specific cases

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

Biocybernetics and Biomedical Engineering

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2017

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Vol. 37, no. 3

528--539

EN

The arterio-venous fistula is a widely accepted vascular access for haemodialysis - a treatment for the end-stage renal disease. However, a significant number of complications (stenoses, thromboses, aneurysms) of fistulas can occur, which are related to the geometry of the anastomosis and the local abnormal hemodynamics. Local flow conditions, in particular the wall shear stress (WSS), are thought to affect sensitive endothelial cells on the inner vessel wall, which leads to intimal hyperplasia. This study presents the results obtained from numerical simulations of the blood flow through three patient-specific end-to-end fistulas which were assessed to be more likely dysfunctional than the end-to side ones. Unsteady and comparative steady-state simulations of blood flow were performed in ANSYS CFX. The obtained results show behaviour of the blood, velocity fields, shear strain, vorticity range, blood viscosity changes, a WSS distribution on vessel walls and give information about the flow rate in the veins receiving blood from fistulas. Blood flow animations are attached to the online version of the paper. Numerical methods seem to be the only opportunity to provide complete information on the distribution and range of the WSS for complicated shapes of blood vessels used to fistula creation, however the WSS is strongly dependent on the local geometry and mesh quality. High values of the shear strain, associated with elevated values of shear stress, found in each model, could increase a risk of haemolysis. High shear environment with raised vorticity can result in activation of platelets and further platelet aggregation and thrombosis.

3

Numerical investigations of the unsteady blood flow in the end-to-side arteriovenous fistula for hemodialysis

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

Acta of Bioengineering and Biomechanics

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2016

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Vol. 18, no. 4

3--13

EN

Purpose: The aim of this study was to investigate the blood flow in the end-to-side arteriovenous (a-v) fistula, taking into account its pulsating nature and the patient-specific geometry of blood vessels. Computational Fluid Dynamics (CFD) methods were used for this analysis. Methods: DICOM images of the fistula, obtained from the angio-computed tomography, were a source of the data applied to develop a 3D geometrical model of the fistula. The model was meshed, then the ANSYS CFX v. 15.0 code was used to perform simulations of the flow in the vessels under analysis. Mesh independence tests were conducted. The non-Newtonian rheological model of blood and the Shear Stress Transport model of turbulence were employed. Blood vessel walls were assumed to be rigid. Results: Flow patterns, velocity fields, the volume flow rate, the wall shear stress (WSS) propagation on particular blood vessel walls were shown versus time. The maximal value of the blood velocity was identified in the anastomosis – the place where the artery is connected to the vein. The flow rate was calculated for all veins receiving blood. Conclusions: The blood flow in the geometrically complicated a-v fistula was simulated. The values and oscillations of the WSS are the largest in the anastomosis, much lower in the artery and the lowest in the cephalic vein. A strong influence of the mesh on the results concerning the maximal and area-averaged WSS was shown. The relation between simulations of the pulsating and stationary flow under time-averaged flow conditions was presented.

4

Angular position determination of heart valves in the pediatric ventricular assist device with use of computational fluid dynamics

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

Aktualne Problemy Biomechaniki

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2014

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z. 8

57--62

EN

This study shows a method than can be used to determine the best angular position of heart valves installed at the inlet and the outlet of a blood chamber during the diastolic phase with use of Computational Fluid Dynamics (CFD). Steady state simulations of the blood flow through the blood chamber of Pediatric Ventricular Assist Device (PVAD) have been performed with ANSYS CFX 14.0. Main assumptions in the present paper have included: motionless discs, rigid walls, non-Newtonian model of blood. The obtained results show that areas of blood stagnation in the blood chamber are smallest for one particular angular position of the inlet valve and are not significantly dependent on the angular position of the outlet valve.

5

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

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

Acta of Bioengineering and Biomechanics

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2014

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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.

6

Numerical analysis of an influence of the artificial valve type on the blood flow inside the ventricular assist device

Klosinski P., Reorowicz P., Obidowski D., Jozwik K.

Computer Methods in Materials Science

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2011

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Vol. 11, No. 1

209-214

EN

A Ventricular Assist Device (VAD) is used in case of severe heart illnesses when the natural heart supplies the body with an insufficient volume of blood. Any damage or improper fiinctioning of the VAD can result in the patienfs death. This implies the constant need to improve the design of VADs and artificial valves which are crucial parts of the device. The authors used the latest Computer Aided Design and Computational Fluid Dynamics software to analyze the flow in the pneumatic Ventricular Assist Device designed at the Foundation of Cardiac Surgery Development and eąuipped with two different types of valves. In the study, a single-disc mechanical artificial heart valve based on the invention of Prof. J.J. Moll, modified at the Institute of Turbomachinery, TU Lodz, was compared with a three-leaflet polyurethane artificial heart. A comparison was made on the basis of the flow visualization inside the VAD chamber and the size of stagnation regions where the flowing blood may coagulate. An angular position of the disc valve was determined on the basis of the previous studies. A steady state simulation was performed on the assumption that walls of the assist device, adapters and valves were rigid. Dynamie viscosity of blood was defined on the basis on the Non-Newtonian Power Law. Simulations were preformed for systole and diastole conditions. The Ansys CFX vi2 code was used to perform preprocessing, solving and postprocessing stages. Deformations of the three-leaflet polyurethane valve were obtained in SolidWorks 2009 and imported to Ansys ICEM v. 12. On the basis of the preformed analysis, it has been proven that the disc mechanical heart valve generates better flow conditions inside the heart chamber, especially if a risk of coagulation is concerned. Moreover, the flow observed inside the chamber when the disc valve was used is more homogenous and a single swirl occurring in the central part enables good washing of the connection of the diaphragm and chamber regions.

PL

Gdy lewa komora serca nie pracuje prawidłowo, to jest zastępowana protezą - pulsacyjną komorą wspomagania pracy serca (VAD, z ang. ventricular assist device), którą często wykonuje się z poliuretanu (PU) i naniesionej za pomocą metody PLD (osadzenie laserem impulsowym) biokompatybilnej powłoki TiN. Otrzymywane duże wartości ściskających naprężeń własnych, są najwyższe ze wszystkich mierzonych, gdy powłokę TiN nanosi się metodą PLD. Celem niniejszej pracy jest opracowanie programu komputerowego wykorzystującego metodę elementów skończonych (MES) do wieloskalowego modelowania stanu odkształceń i naprężeń dla komory krwistej zbudowanej z PU/TiN, który to program będzie wykorzystywany do określania najbardziej niebezpiecznych miejsc ze względu na możliwe uszkodzenia materiału powierzchni komory, jakie mogą się pojawiać w warunkach pracy komory. Algorytmy wykorzystywane do tworzenia siatki elementów skończonych, implementacja warunków brzegowych i otrzymane rozwiązanie numeryczne zaprezentowano w niniejszej pracy. Opracowany kod MES jest oparty na nowym podejściu do symulowania materiałów wielopowłokowych otrzymywanych metodą PLD. Model w skali mikro zawiera dwa składniki: model naprężeń własnych (naprężeń początkowych) powstałych w procesie nanoszenia powłok i model obciążeń zadawanych w komorze krwistej VAD. Przewidywane w modelu rozkłady naprężeń i odkształceń pomagają określić dokładnie te strefy komory krwistej, które można zdefiniować, jako obszary będące źródłem jej uszkodzeń

7

Numerical Study of a Flow in the Cerebral Arterial Circle

Obidowski D., Jozwik K., Reorowicz P.

Computer Methods in Materials Science

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2009

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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.