Hemodynamics of venous valve pairing and implications on helical flow.

BACKGROUND: It has been shown that venous valves have pairing arrangements with specific relative orientation and spacing that contribute to helical flows. The studies to date have not quantified the hemodynamic impact of helical flow formation. A computational model allows various valve orientations and spacings to be studied to better understand the hemodynamic effect of valve pairing.

METHODS: Simulations were performed for paired valves at physiologically relevant spacing and orientations to study the flow features and hemodynamics associated with valve pairing configurations. The wall shear stress (WSS), residence time, and pressure drop were evaluated for the various valve pairing cases.

RESULTS: It was found that the WSS on the lumen flow side (front) of the leaflet is several times higher than on the valve pocket side (back). With orthogonal paired valves, the WSS at the critical back side is increased. Helical flow was clearly observed only with orthogonal valve pairing. The residence time was reduced to less than half (0.47 vs 1.16 seconds) in the orthogonal valve case compared with the parallel valve cases. The farther spaced valves (6 cm) had the highest residence time.

CONCLUSIONS: This simulation study shows that helical flow in the veins of lower extremities is strongly dependent on the relative orientation and spacing of the valves. For optimal orientation (∼90 degrees) and spacing (∼4 cm), strong helical flow is seen, which enhances WSS and reduces the flow resistance and residence time. These findings demonstrate a structure-function relation that optimizes flow patterns in normal physiology, which can be compromised in venous valve disease. The results of this study provide valuable insights that improve the current understanding of blood flow patterns around venous valves and the design of future multiple paired prosthetic valves.