[Computational-fluid-dynamical analysis of the flow field of forearm flap with four types of venous anastomotic techniques].

Purpose: Using the computational fluid dynamics to analyse the alteration of flow field of free forearm flap with 4 different venous anastomotic techniques, and to preliminarily explore its clinical significance.

Methods: Three dimensional geometric models of radial forearm flap with 4 types of anastomotic techniques between radial vein and recipient vessels were established by Pro/E (Wildfire 4.0) as follow: type I(matched anastomosis), type II(stump anastomosis), type III (angular anastomosis) and type IV(end-to-side anastomosis). Then the established geometric models were transferred to the SC/Tetra 8.0 software for mesh generation and calculation. Porous model was applied to the flap to simulate capillary structure as before, inlet velocity of radial artery was set as 20mm/s and outlet pressure of recipient vein as 0 Pa. By comparing pressure and velocity distribution on different cross sections of blood vessels, hemodynamic feature of the flap with 4 types of anastomotic techniques was studied, focusing on the alternation of flow field of drainage system of the flap, especially at the anastomotic sites. The data was analysed using SAS8.0 software package for ANOVA.

Results: The pressure on the four sections of the flap circulatory system was significantly higher in type I compared with type II, III and IV (F=40.99,P<0.001). Type II presented with vortex in the anastomotic site, and type III,IV with smooth flow. Type IV had an absorption effect at the anastomotic site. The pressure loss of the flap circulation was maximal in the radial vein of vascular pedicle(F=97.00,P<0.001).

Conclusions: Type III and IV are considered appropriate techniques to deal with caliber discrepancy of recipient site. Theoretically, reasonable reduction of the vascular pedicle length and choice of the concomitant radial vein with wider radius for anastomosis can effectively decrease the resistance of circulation in the flap.