The effect of in-plane arterial curvature on blood flow and oxygen transport in arterio-venous fistulae

Abstract

Arterio-Venous Fistulae (AVF) are the preferred method of vascular access for patients with end stage renal disease who need hemodialysis. In this study, simulations of blood flow and oxygen transport were undertaken in various idealized AVF configurations. The objective of the study was to understand how arterial curvature affects blood flow and oxygen transport patterns within AVF, with a focus on how curvature alters metrics known to correlate with vascular pathology such as Intimal Hyperplasia (IH). If one subscribes to the hypothesis that unsteady flow causes IH within AVF, then the results suggest that in order to avoid IH, AVF should be formed via a vein graft onto the outer-curvature of a curved artery. However, if one subscribes to the hypothesis that low wall shear stress and/or low lumen-to-wall oxygen flux (leading to wall hypoxia) cause IH within AVF, then the results suggest that in order to avoid IH, AVF should be formed via a vein graft onto a straight artery, or the inner-curvature of a curved artery. We note that the recommendations are incompatible—highlighting the importance of ascertaining the exact mechanisms underlying development of IH in AVF. Nonetheless, the results clearly illustrate the important role played by arterial curvature in determining AVF hemodynamics, which to our knowledge has been overlooked in all previous studies.

Wall shear stress exposure time: a Lagrangian measure of near-wall stagnation and concentration in cardiovascular flows

“…The local transport of several substances near and at the vessel wall are known to influence atherosclerosis progression [56]. For example, previous studies have looked into transport of low density lipoproteins (LDL) [17,20,30,14], high density lipoproteins (HDL) [40,24], oxygen [16,27], nitric oxide (NO) [45,35], monocytes [12,14], and adenine triphosphate ATP and adenine diphosphate ADP [13,15,8] as important mass transport processes involved in atherosclerosis.Intravascular thrombosis is another compelling pathology associated with most cardiovascular diseases where near-wall transport becomes important [7,25]. The trajectories of individual platelets and the accumulation and residence time of chemical solutes including ADP, thrombin, and various blood factors control clot formation.…”

The Influences of Swirl Flow on Fractional Flow Reserve in Mild/Moderate/Severe Stenotic Coronary Arterial Models

“…(1), (2) [10,14,20]. Orthogonal views of a helically sinuous tube part and a stenotic part are shown in Fig.…”

Suppressing unsteady flow in arterio-venous fistulae

“…The artery was constructed by sweeping a circular section with diameter D a = 5 × 10 −3 m along a plane-arc centreline x a , defined as 42 who showed that arterial curvature can have a significant impact on unsteadiness in AVF. The vein was constructed by sweeping a circular section with diameter D a along a two-piece cubic hermitian spline x defined as…”

“…This finding appears to have inspired development of an externally mounted device to help maintain an acute anastomotic angle. 57 More recently, CFD simulations in idealised configurations with an acute anastomotic angle of 35 • were undertaken by Browne et al 43,44 Results exhibited unsteady flow in both the artery and vein, as did results from simulations in four more realistic configurations undertaken by Bozzetto et al 48 Finally, Iori et al 42 used CFD simulations in idealised configurations to demonstrate that forming an AVF by connecting a vein onto the outside of an arterial bend could suppress highfrequency unsteadiness inside the artery. However, flow within the venous section, where pathology is also known to develop, typically remained unstable, and a recent follow-on study by Grechy et al, 55 in more realistic configurations, suggested that unsteady flow is present throughout such configurations at certain points in the pulse cycle.…”

“…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.…”