The use of helix geometry for arterial grafts has been proposed on the hypothesis that by intentionally inducing swirling or spiral flow in the grafts, hemodynamic performance of the grafts might be improved. To investigate their hemodynamic performance, the present study numerically simulated the flows in the helical grafts, not only for comparison with conventional grafts but for their parameter analysis of Dean Number, helical pitch, and amplitude. Results showed that the helical graft achieved three dimensionality swirling flow, more uniformly distributed flow field and high wall shear stress (WSS) which continued in the straight part of the graft downstream. However, increased pressure drop was predicted in helical graft; flow areas with low velocity will concentrate in one corner, which might possibly suffer from flow stagnation and inhabitation, leading to a possible vulnerability to hemodynamic failure, intimal hyperplasia (IH) and thrombosis. The parameter study indicates that even at the same Dean number but with different geometry, the hemodynamic performance of two grafts are totally different. Shorter helical pitch and larger helical amplitude do improve the graft's hemodynamic performance, but may not be mechanically robust or applicable clinically. The current study increases fundamental understanding of the flow mechanism in swirling flow grafts.

Foam sclerotherapy is a widely used treatment for varicose veins. However, complications caused by poor foam stability still remain. Most studies ignore multiple influencing factors and only study a single factor. Furthermore, a stable foam preparation using different preparation conditions has not been developed. This study aimed to explore the changing laws of foam stability under multifactorial conditions, and to determine the influence of various factors and optimal preparation conditions on the half-life of foam. A two-level orthogonal test was conducted using four factors (syringe size, surfactant, preparation temperature, and pump speed). Classifications were established as follows: syringe sizes, 2.5 mL and 5 mL; surfactant concentrations, 6% and 0%; preparation temperatures, 20 °C and 10 °C; and pump speeds, 250 mm/s and 125 mm/s, respectively. Eight experimental group (EG) multi-factor combinations were tested. Half-life and drainage time were recorded for analysis. The initial drainage time was within 200 s, but the difference between the groups was also about 200 s. The drainage rate curves of all EGs gradually increased over time. Conversely, the foam half-life extended by about 10 times for the four factors. In addition, the analyses revealed that the order of influence was surfactant >temperature >pump speed >syringe size. The most stable foam preparation was determined. Syringe size, surfactant, temperature, and pump speed had markedly observable influences on foam half-life. A combination of multiple factors can be used to prepare a more stable foam in clinical scenarios and to suitably superimpose favorable conditions to avoid unfavorable conditions.

Preliminary studies on an individual helical graft indicated that its hemodynamics might be improved while pressure drop increased compared with a traditional graft. Aiming to investigate whether the benefits of a helical graft to hemodynamics dominate its deficits, this study numerically carried out comparative study of helical-type artery bypass graft (ABG) and traditional-type ABG under both steady and pulsatile flow conditions. The results showed that a helical-type ABG resulted in reduced oscillating shear index, improved wall shear stress, enhanced flow mixing and three-dimensionality, and improved flow behavior at the distal anastomosis and occluded section of the host vessel compared with traditional-type ABG. More important, although a helical-type ABG did increase the pressure drop compared with a traditional one, its maximum percentage increase during a cardiac cycle was <21% which is still within physiological sense. Therefore, we believe that the adoption of helical bypass could help to prevent intimal hyperplasia (IH) and thrombosis at the distal anastomosis and improve the graft patency while keeping clinical maintenance. This investigation provided an important basis for the clinical applications and theory support of helical graft.