Assessing the disturbed flow and the transition to turbulence in the arteriovenous fistula.

The arteriovenous fistula (AVF) is the main form of vascular access for hemodialysis patients, but its maintenance is very challenging. Its failure is mainly related to intimal hyperplasia, leading to stenosis. The aim of this work is twofold: i) to perform a computational study for the comparison of the disturbed blood dynamics in different configurations of AVF and ii) to assess the amount of turbulence developed by the specific geometric configuration of AVF. To this aim, we reconstructed realistic 3D geometries of two patients with a side-to-end AVF, performing a parametric study by changing the angle of incidence at the anastomosis. We solved the incompressible Navier-Stokes equations modeling the blood as an incompressible and Newtonian fluid. Large Eddy Simulations (LES) were considered to capture the transition to turbulence developed at the anastomosis. The values of prescribed boundary conditions are obtained from clinical Echo-Color Doppler measurements. To assess the disturbed flow, we considered hemodynamic quantities such as the velocity field, the pressure distribution, and wall shear stresses derived quantities, whereas to quantify the transition to turbulence, we computed the standard deviation of the velocity field among different heartbeates and the turbulent kinetic energy.