NUMERICAL SIMULATION OF THE HEMODYNAMICS IN 6 MM AND 6-8 MM HEMODIALYSIS GRAFTS AND INVESTIGATION OF BIOMECHANICAL CONSEQUENCES

摘要

Hemodialysis vascular access dysfunction is still considered as a major cause of morbidity and mortality in hemodialysis patients. The most common cause of this vascular access dysfunction is venous stenosis secondary to the progression of venous intimal hyperplasia at the graft-vein junction or in the draining vein. The geometry of the vessels and the local hemodynamics are believed to be contributory factors in the development of intimal hyperplasia. In the present study, the hemodynamic parameters in two types of vascular access grafts of different diameters: 6 mm and 8 mm tapered to 6 mm at the arterial site were compared. A three-dimensional CFD model was developed to simulate blood flow in the two graft types. The boundary conditions applied were a pulsatile velocity waveform at the arterial inlet and a pulsatile pressure waveform at the venous outlet. Computational fluid dynamics software was used to solve the time dependent Navier-Stokes equations under physiological conditions in both graft types. Since the cross section area and the diameter of the venous side of the tapered graft are larger than those of the straight one, the flow aligns well with the vein downstream of the graft and hence the smaller vortices are generated. Comparing the parameters at the two venous anastomosis regions also indicates that in spite of the higher flow rate in 6-8mm tapered graft, the velocity and the wall shear stress values are lower than the values of the 6 mm straight graft.