[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.

[Establishment of hemodynamic model of human radial forearm free flap].

PURPOSE: To preliminarily establish a hemodynamic 3D numeric model of radial forearm free flap with vascular pedicle of radial artery and vein, and discuss its scientific workability. METHODS: The 3D geometric model of 50mm×80mm×10mm radial forearm flap was established by Pro/E(Wildfire 4.0). The vascular pedicle was 50mm in length including radial artery (inside diameter was 1.9mm) and concomitant radial vein (inside diameter was 0.84mm). The half-embedded vessels went hrough the flap paralleling the long axis. Then the established geometric model was transferred to the SC/Tetra 8.0 software for mesh generation and calculation. According to the virtual flow volume of the radial artery, the inlet velocity was set as 20mm/s. With the different blood pressure of 53mmHg between the feeding artery and draining vein, the tentative porous values were achieved. Then porous model was applied to the flap to simulate the capillary structure. The pressure distribution on the central axis of radial artery and vein and the radial velocity distribution in three different cross sections of vessels were figured out. RESULTS: A model with 10355473 meshes and 2104014 nodes was built. When porous model was applied, the pressure difference between radial artery and vein was calculated to 7050 Pa (52.8mmHg), which was close to clinical value. The computational fluid dynamic analysis results showed that with porous model, the central pressure of radial artery was continuously kept to a higher level. When blood flowed in and flows out of the flap, the blood velocity decreased and increased greatly. While the central pressure of radial vein significantly decreased at the moment of blood flowing out of the flap. These results basically agreed with the features of normal blood circulation of the forearm flap. CONCLUSIONS: Porous model effectively simulates hemodynamic status of forearm flap, which provides a new method for the study of mechanism of blood circulation in radial forearm flap and also lays a foundation for the following hemodynamic study of vascular anastomosis.