Vascular Remodeling in Autogenous Arterio-Venous Fistulas by MRI and CFD

Abstract

Hemodynamic parameters play an important role in regulating vascular remodeling in arterio-venous fistula (AVF) maturation. Investigating the changes in hemodynamic parameters during AVF maturation is expected to improve our understanding of fistula failure, but very little data on actual temporal changes in human AVFs is available. The present study aimed to assess the feasibility of using a noncontrast-enhanced MRI protocol combined with CFD modeling to relate hemodynamic changes to vascular remodeling following native AVF placement. MR angiography (MRA) and MR velocimetry (MRV) data was acquired peri-operatively, 1 month, and 3 months later in three patients. Vascular geometries were obtained by segmentation of the MRA images. Pulsatile flow simulations were performed in the patient specific vascular geometries with time-dependent boundary conditions prescribed from MRV measurements. A principal result of the study is the description of WSS changes over time in the same patients. The disturbed flow observed in the venous segments resulted in a variability of the WSS distribution and could be responsible for the non-uniform remodeling of the vessel. The artery did not show regions of disturbed flow upstream from the anastomosis, which would be consistent with the uniform remodeling. MRI use demonstrated the ability to provide a comprehensive evaluation of clinically relevant information for the investigation of upper extremity AVFs. 3D geometry from MRA in combination with MRV provides the opportunity to perform detailed CFD analysis of local hemodynamics in order to determine flow descriptors affecting fistula maturation.

New Insights into Dialysis Vascular Access: Molecular Targets in Arteriovenous Fistula and Arteriovenous Graft Failure and Their Potential to Improve Vascular Access Outcomes

“…Magnetic resonance imaging and computed tomography have been used in both large-animal and clinical studies to evaluate neointimal hyperplasia development, lumen geometry, hemodynamics, and computational fluid dynamics (34,(64)(65)(66). These imaging technologies would be even more powerful if they could be applied in transgenic rodent models where the combination of pathobiology and computational fluid dynamics modeling could be studied in greater depth.…”

Novel Paradigms for Dialysis Vascular Access

“…The next step in these investigations should be the use of image-based CFD analyses to document WSS patterns in patient-specific models of AVF during vascular access follow-up (58,59), aimed at identifying areas at risk for development of neointimal hyperplasia. Moreover, with the advent of parallel processors power and new CFD solvers including fluid-structure interaction, vessel wall elasticity could be modeled in pulsatile simulations toward the understanding of the influence of wall compliance on the pattern of disturbed flow in AVF.…”

Suppressing unsteady flow in arterio-venous fistulae

“…first 15 Fourier modes were extracted, and the signal was scaled such that the peak Reynolds number at the PAI was 1300, in agreement with Ref. 49. The resulting time-averaged Reynolds number at the PAI was ∼750, similar to the time-constant PAI Reynolds number of 800 used during the optimisation process.…”

“…These were selected using an approach similar to Pant et al 78 such that P DAO had a physiological range 80-130 mm Hg, and flow splits were similar to those of Sigovan et al, 49 with an average flow split between the DVO and DAO of ∼66:34, a minimum flow split between the DVO and DAO of ∼37:63 at the beginning of the acceleration phase, a maximum flow split between the DVO and DAO of ∼99:1 at the end of the deceleration phase, and a flow split between the DVO and DAO at peak inflow of ∼45:55. Specifically, the RCR values were obtained using an iterative approach that aimed to minimise where P PAI is the pressure waveform at the PAI, P RS = 130 mm Hg, and P RD = 80 mm Hg are reference systolic and diastolic pressures, respectively, at the PAI, Q R is a reference outflow rate waveform at the VO taken from Sigovan et al, 49 and the integrals are taken to be over a single pulse, when the solution has become period independent. The iterative process itself combined a 0D lumped parameter model, with a low-resolution time-dependent 3D flow model.…”

“…25 More recent work, undertaken specifically in the context of vascular fluid mechanics, includes studies of stenotic flows, 26 pulsatile flow in curved pipes, [27][28][29][30] flow in helical pipes, [31][32][33][34] and flow at junctions. [35][36][37] In terms of simulating flow in AVF configurations, there have been a range of previous Computational Fluid Dynamics (CFD) studies, including 1D simulations, [38][39][40] 2D simulations, 41 3D simulations with rigid walls in idealised geometries, [42][43][44][45][46][47] 3D simulations with rigid walls in more realistic geometries, [48][49][50][51][52][53][54][55] and simulations with distensible walls. 56 Of these studies, several investigated flow unsteadiness.…”