Computational Analysis of Anastomotic Angles by Blood Flow Conditions in Side-to-End Radio-Cephalic Fistulae Used in Hemodialysis

Janaína De Andrade Silva,José Karam-Filho,Carlos Cristiano H Borges

doi:10.4236/jbise.2015.83013

Abstract

Chronic renal failure is a disease that affects a considerable population percentage that requires the hemodialysis procedure which is a blood filtration. This process is extremely stressful in many cases for the patient, because there is a continuous degradation of vessels and fistulae susceptible to this process due to the alterations of the stress at the blood vessel walls and flow patterns, leading to diseases such as intimal hyperplasia and consequent stenosis. Experimental in vivo researches in this area are very difficult to perform. In this sense computational models become interesting non invasive options to understand what happens to the blood in non viscometric geometries. In this work, we analyse blood flow, through computational modeling, in arteriovenous fistulae used in hemodialysis, using geometries with dimensions close to real ones. Discretization of the governing equations was made through a finite volume technique with the PISO—Pressure Implicit with Splitting of Operators—algorithm, using as a basis the OpenFOAM software platform. Large vessel Newtonian fluid model was used to analyze six possible anastomotic angles (20。, 25。, 30。, 35。, 40。, 45。). To analyze the possibility of stenosis formation caused by hyperplasia, results for wall shear stress, oscillatory shear index (OSI), velocity and local circulation fields were obtained, showing that higher angles presented more secondary flows and larger extensions of stagnation regions near the critical areas of the junctions. Moreover, a range around 25。was identified to be the most suitable choice for clinical applications, minimizing possibility of diseases.

Highlights

Chronic renal failure is a disease in which partial loss of the kidney function occur in a slow, progressive and irreversible way
In this work, aiming to contribute to the investigation of better anatomical configurations that could generate more favorable hemodynamic conditions, to minimize the problems related with fistulae failures, computational analyses are performed considering six medium to small anastomotic angles: 20 ̊, 25 ̊, 30 ̊, 35 ̊, 40 ̊ and 45 ̊, before any stenosis or other pathologies have started
It is observed that for higher angles, from 35 ̊ to 45 ̊, dense and large extents of stagnation regions are formed near the heels of the fistulae

Summary

Introduction

Chronic renal failure is a disease in which partial loss of the kidney function occur in a slow, progressive and irreversible way. As a leading alternative treatment for this deficiency, the blood filtering process called hemodialysis is used. This is a process which consists in filtering blood and removing impurities from this fluid, similar to the process executed by the kidney. The blood is first transported through a venous access connected to an artificial arterial fistula and subsequently the blood passes through the dialysis process being filtered [1]. In this case, the chronic renal failure patient may undergo various disorders such as nausea and loss of venous access, among others. The problems related to fistulae are believed to be caused due to friction generated by the shear forces of blood on the vessel walls, causing diseases like intimal hyperplasia and thrombosis [2] [3]

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