Anastomotic Size Mismatch—Modeling of the Hemodynamics of Idealized Constructs by Means of Computational Fluid Dynamics

One criterion for selection of recipient vessels in microvascular surgery is size match. Abrupt changes in vessel diameter are thought to predispose to thrombus formation and early anastomotic failure, although experimental data are lacking. Where mismatch cannot be avoided, a number of surgical techniques have been described. The aim of this study was to numerically model the hemodynamics of four different techniques used to anastomose small arteries to larger.

Four idealized models of 1-mm diameter arteries anastomosed to 2-mm arteries were constructed: (a) sleeve, (b) fish-mouth, (c) wedge, and (d) oblique cut. Flow was considered laminar and Newtonian, and vessel walls were considered non-compliant. Flow rate was recorded from the femoral artery of the rat. Constant whole blood viscosity and density were specified as 0.005 kg/ms and 1059 kg/m³, respectively. Flow path lines and wall shear stresses were calculated using the commercially available computational fluid dynamics (CFD) code Fluent™.

Regions of separated flow were observed for all configurations but the wedge. The sleeve and fish-mouth configurations displayed similar regions of separated flow, whereas the oblique cut exhibited a more complex re-circulating flow structure. There were dramatic changes in vortex size and strength due to the unsteady nature of the flow. Although the wall shear stress distribution was different for each configuration, the maximum wall shear stress value was very similar.

While caution must be exercised when extrapolating results from these idealized CFD models into patterns of blood flow within compliant vessels, it can be concluded that the wedge configuration demonstrated the least flow separation.