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.
Highlights
Patients with End-Stage Renal Disease (ESRD) suffer from an irreversible reduction in kidney function
If one subscribes to the hypothesis that unsteady flow causes Intimal Hyperplasia (IH) within Arterio-Venous Fistulae (AVF), 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
If one subscribes to the hypothesis that low wall shear stress and/or low lumen-to-wall oxygen flux cause IH within AVF, 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
Summary
Patients with End-Stage Renal Disease (ESRD) suffer from an irreversible reduction in kidney function. Blood is drawn from the patient through a vascular access, and circulated through a dialysis filter to remove metabolic waste, before being returned to the body. The “gold-standard” method for creating a vascular access is formation of an Arterio-Venous Fistula (AVF). AVF are arterio-venous connections commonly formed surgically in the wrist or upper arm by connecting or “anastomosing” a vein onto an artery. The large pressure difference between the artery and vein leads to increased blood flow through the vein, which in turn will (ideally) cause the vein walls to strengthen and the vein itself to enlarge. The result—an enlarged “arterialized” vein, with strengthened walls, and a high blood flow rate—can accommodate a large gauge needle, and provide excellent access for hemodialysis over a period of several years
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