A comparative study of the hemodynamics in two types of grafts of 6 mm versus 6-8 mm as an upper arm straight graft hemodialysis access

Abstract

Hemodialysis vascular access failure considered as a primary cause of morbidity and hospital admissions for chronic hemodialysis patients. Clearly the hemodynamics within a vascular access graft and also the anastomotic geometry induced disturbed flow patterns have a substantial influence on the initiation and development of "intimal hyperplasia" the most common cause of vascular access failures. The present study is intended to investigate and compare the hemodynamics in two types of hemodialysis vascular access grafts of different diameters: 6 mm straight versus 8 mm tapered to 6 mm at the arterial site in an upper arm brachio-axillary prosthetic graft in straight configuration. Using a three-dimensional CFD model of an upper arm straight vascular access graft the two graft types have been compared in terms of overall flow pattern, wall shear stress distribution and other hemodynamic parameters. The boundary conditions applied are a physiological pulsatile velocity waveform at the arterial inlet and a pulsatile pressure waveform at the venous outlet. Results show higher values of wall shear stresses at the arterial amastomosis region of the 6-8 mm tapered graft over its 6 mm straight graft counterpart. Comparing the parameters at the two venous anastomosis regions indicates that in spite of the higher flow rate in 6-8 mm tapered graft, the velocity and the wall shear stress values are lower than the values of the 6 mm straight graft. The larger diameter and hence the larger venous anastomotic length of the tapered 6-8 mm graft let the flow align well with the vein downstream of the graft with less perturbation and thereby smaller the vortices generated and lower the wall shear stress values at the vein floor opposite to the graft outflow in comparison with the straight 6 mm graft. © 2010 International Federation for Medical and Biological Engineering.