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An arteriovenous fistula (AVF), a vascular structure surgically created to enable haemodialysis, is commonly affected by stenosis in the juxta-anastomotic region. A new treatment involving the implantation of a flexible stent has shown good potential for retaining healthy AVFs. Since vascular disease in the AVF is known to be related to the haemodynamic environment within the vasculature, this study aims to understand the impact of the stent implantation on the flow dynamics within a single patient-specific AVF. A virtual stented geometry of the AVF was obtained with micro-CT images of a benchtop AVF model implanted with a Supera stent. Reynolds averaged Navier–Stokes simulations were conducted with physiological boundary conditions (Reynolds numbers varying from 345 to 730) applied on the AVF model with and without the presence of the stent. Velocity contour slices within the vein showed the concentration of high velocity in the stent encapsulated region. Moreover, the ratios of flow rate across the stent-lumen cross-sections over the flow rate across the vessel-lumen cross-sections suggested that the flow was being funnelled through the stent encapsulated regions of a malapposed section, despite the porous structure of the stent. A larger low velocity recirculation region translated to a larger vessel wall area of high Oscillatory Shear Index (OSI) and low Time-Averaged Wall Shear Stress (TAWSS) in the AVF model with the stent absent, compared to the stented model. This suggested that the adverse haemodynamic behaviour was being funnelled away from the vessel wall, possibly leading to a protective environment in the malapposed region of the vein.

The arteriovenous fistula (AVF), which is a vasculature created for end-stage renal disease patients who require haemodialysis, is susceptible to many vascular diseases. It is well known that disturbed hemodynamics is a factor in the initiation of vascular disease; however, only a limited number of experimental studies have been conducted to assess the flow behaviour within the AVF. The current study is an investigation of the complex three-dimensional flow within a physiological AVF geometry, using tomographic particle image velocimetry. To this end, a benchtop model of a patient-specific geometry was created by casting silicone around a soluble 3D print of the vessels. The patient-specific boundary conditions were reproduced by driving a refractive-index matched working fluid from a pulsatile pump, which was connected to the model via a tubing network inclusive of valves and compliance chambers. The seeded working fluid was illuminated with a 1 kHz double-pulsed laser, and four high-speed cameras placed at optimised locations were used to capture the particle images, with the volume reconstructions refined by a 3D internal mask created using morphological operations. The velocity magnitude contour plots of the resulting vector field revealed two zones of low velocity in the anastomosis, while locations of high turbulent kinetic energy are observed in the anastomosis and venous regions. These results suggested that the collision of the two opposing inlet flows and the curvature at the anastomosis cause disturbance in the flow that is carried downstream. Graphic abstract : [Figure not available: see fulltext.]

An arteriovenous fistula (AVF) is a surgically created vasculaturefor end stage renal disease patients who require haemodialysis.The AVF is susceptible to high failure rates mainly dueto the onset of intimal hyperplasia which is known to be linkedto disturbed hemodynamics. One method adopted to treat thiscondition is to implant a flexible stent in the diseased region.In the present study, a silicone model of a patient-specific AVFwas implanted with the Supera stent and subsequently scannedusing a micro-CT. Using the segmentation of the high resolutionscan, the AVF geometry with the stent detail was recreated andReynolds averaged Navier Stokes simulations were conductedwith pulsatile inlet flows of Reynolds numbers ranging from345 to 730. Subsequently, two low velocity zones which translatedto low wall shear stress zones were identified in the AVF.Other flow behaviour such as twisting flow from the high flowzones to low flow zones were also apparent. This study formsthe basis to extend into large eddy simulations to detail the flowdisturbances in the AVF to better understand the impact of thestent on the AVF health.