Analysis of the Optimum Tapering Angle in Microanastomosis Using Computational Fluid Dynamics

Background: In free flap transfer, size discrepancy between the vascular pedicle and recipient vessel can create a problem for microsurgeons and sometimes induces postoperative thrombus formation. When there is a major difference between the diameters of the vascular pedicle and the recipient vessel, the larger vessel is often tapered to perform the anastomosis properly. However, the decision on the tapering angle used depends mostly on the operator’s experience. In this study, computational fluid dynamics (CFD) was used to investigate the optimum tapering angle. Methods: Using ANSYS ICEM 16.0 (ANSYS Japan, Tokyo, Japan), simulated vessels of diameters 1.5 mm and 3.0 mm were designed and then used to produce four anastomosis models with the 3.0-mm vessel tapered at angles of 15º, 30º, 60º, and 90º (no tapering). Venous perfusion with a mean value of 13.0 mL/min was simulated, and this was passed through the four anastomosis models in both the forward direction (F), from the smaller to the larger vessel, and the retrograde direction (R), from the larger to the smaller vessel. The velocity, wall shear stress (WSS), and oscillatory shear index (OSI) were measured in these eight patterns and then analyzed using OpenFOAM version 5. Results: The decrease in velocity was limiting. The WSS was greater in the R direction than the F direction at every tapering angle. The OSI also tended to be almost the same in the F direction, and lower at smaller tapering angles in the R direction. And, it was greater in the F direction than in the R direction at every tapering angle. The OSI values for 15º and 30º were almost identical in the R direction. Conclusion: The risk of thrombus formation is thought to be lower when tapering is used for anastomosis if the direction of flow is from the larger to the smaller vessel, rather than vice versa. These results also suggest that the optimum tapering angle is approximately 30º in both directions

Comparison of Antera 3D® and TcPO2 for Evaluation of Blood Flow in Skin

Background: There is a need for quick skin blood flow tests that can be performed in the wound healing field. Antera 3D® is a compact scanner using multispectral imaging. It can perform quick assessment of skin conditions. The purpose of the present study was to investigate the ability of the Antera 3D® to assess skin blood flow in comparison with transcutaneous partial pressure of oxygen (TcPO2) measurements. Methods: This study was conducted on 13 patients with a history of lower extremity ulcers. Measurements of hemoglobin average level (hereafter, Hb score) measured by Antera 3D® and TcPO2 measured by a transcutaneous blood gas monitor were obtained at the same sites on the dorsal foot and lower leg. Differences in Hb score and TcPO2 were analyzed by t-test for each measurement site and for the presence of peripheral arterial disease (PAD). The correlation between TcPO2 and Hb score was analyzed by Pearson’s correlation coefficient. Results: Twenty-four limbs were tested. Hb score was higher (P < 0.001) and TcPO2 was lower (P = 0.056) in the dorsal foot compared to the lower leg. In the dorsal foot, Hb score was higher (P = 0.023) and TcPO2 was lower (P = 0.046) in patients with PAD compared to those without PAD. A significant negative correlation (r = –0.68; 95% confidence interval –0.85 to –0.38, P < 0.001) between TcPO2 and Hb score was observed in the dorsal foot. Conclusion: The negative correlation between TcPO2 and Hb score may reflect compensatory peripheral vasodilation due to occlusion or stenosis of central arteries. This study showed that Hb score measured by Antera 3D® may be related to skin blood flow