عنوان مقاله [English]
Regarding the major determinant of Anastomosis angle in the efficiency of fistula for dialysis, obtuse angle Anastomosises are designed and simulated with angles of90,120,135and145 degree and the obtained results are evaluated from standpoint of flow patterns at the region of the Anastomosis and shear stress in the fistula wall. In this study, in order to compare obtained results in fistula, two Newtonian and carreau non-Newtonian blood models are used at maximum flow rate of blood pulsation curve (flow rate at the time of0.2and0.4seconds respectively). At angle of 90degrees, the formed vortices dimensions, due to the separation of the flow during passing through the region of the Anastomosis, significantly larger than obtuse angles. Consequently, the probability of deposition in the region of the flow increases sharply. from the standpoint of flow pattern, the 90degree angles are inappropriate Anastomosis angle for fistula. At the obtuse angles, the dimensions of these vortexes become much smaller, and then the obtuse angles are considered a better choice. From the standpoint of maximum shear-stress, Anastomosis with obtuse angles in comparison with the Anastomosis angle of 90degrees, has lower maximum shear stress values and the range involved in the maximum shear stress in Anastomosis with 90degree is much wider than the range of Anastomosis with the obtuse. Hence, the probability of manifestation of thrombosis (the main factor of fistula failure) is much higher. In this simulation, the results related to the Newtonian and non-Newtonian models are very close, and the non-Newtonian model predicts shear stress slightly more.