The effect of proximal artery flow on the hemodynamics at the distal anastomosis of a vascular bypass graft: Computational study

The formation of distal anastomotic intimal hyperplasia (IH), one common mo de of bypass graft failure, has been shown To occur in the areas of disturb ed flow particular to this sire. The nature of the flow in the segment of a rtery proximal to the distal anastomosis varies from case to case depending on the clinical situation presented A partial stenosis of a bypassed arter ial segment may allow residual prograde flow through the proximal artery en tering the distal anastomosis of the graft. A complete stenosis may allow f or zero flow in the proximal artery segment or retrograde flow due to the p resence of small collateral vessels upstream. Although a number of investig ations an the hemodynamics at the distal anastomosis of an end-to-side bypa ss graft have been conducted, there has not been a uniform treatment of the proximal artery flow condition. As a result, direct comparison of results from study to study may nor be appropriate. The purpose of this work was to perform a three-dimensional computational investigation to study the effec t of the proximal artery flow condition (i.e., prograde, zero, and retrogra de flow) on the hemodynamics at the distal end-to-side anastomosis. We used the finite volume method to solve the full Navier-Stokes equations for ste ady flow through an idealized geometry of the distal anastomosis. We calcul ated the flow field and local wall shear stress (WSS) and WSS gradient (WSS G) everywhere in the domain, We also calculated the severity parameter (SP) , a quantification of hemodynamic variation, at the anastomosis. Our model showed a marked difference in both the magnitude and spatial distribution o f WSS and WSSG. For example, the maximum WSS magnitude on the floor of the artery proximal to the anastomosis for the prograde and zero flow cases is 1.8 and 3.9 dynes/cm(2), respectively, while it is increased to 10.3 dynes/ cm(2) in the retrograde flow case, Similarly: the maximum value of WSSG mag nitude on the floor of the artery proximal to the anastomosis for the progr ade pou case is 4.9 dynes/cm(3), while it is increased to 13.6 and 24.2 dyn es/cm(3), respectively, in the zero and retrograde flow cases. The value of SP is highest for the retrograde flow case (13.7 dynes/cm(3)) and 8.1 and 12.1 percent lower than this for the prograde (12.6 dynes/cm(3)) and zero ( 12.0 dynes/cm(3)) flow cases, respectively. Our model results suggest that the flow condition in the proximal artery is an important determinant of th e hemodynamics at the distal anastomosis of end-to-side vascular bypass gra fts. Because hemodynamic forces affect the response of vascular endothelial cells, the flow situation in the proximal artery may affect IH formation a nd, therefore, long-term graft patency. Since surgeons have some control ov er the flow: condition in the proximal artery, results from this study coul d help determine which flow condition is clinically optimal.