Aim: During lower limb immobilization, patients are at risk to develop deep venous thrombosis. Recently, a water-pad was developed that should counteract venous stasis. The water-pad, located under the plaster, mobilizes water from the foot to the calf during weight bearing and, thereby, imitates muscle pump function. The purpose of this study was to assess the effect of the water-pad on venous pump function in healthy individuals.
Methods: In 21 healthy subjects (10 men and 11 women) both legs were plastered. Venous pump function was assessed by plethysmography measuring lower leg venous ejection fraction and volume. Subjects were tilted from the supine position to upright standing to determine total venous volume. Hereafter, stepping was performed to measure venous ejection fraction and volume under different filling conditions of the water-pad (0, 50, 100, 150, 200, 250 and 300 mL). Different sizes of water-pads (small, medium and large) were applied to each plastered leg in order to test the effectiveness and to relate optimum size to anthropometrical data.
Results: The venous ejection fraction increased significantly from 30 +/- 17% to a maximum of 42 +/- 19% during stepping with increasing filling condition (RM anova; P = 0.009). Ejection volume also enhanced significantly during stepping with increasing filling condition from 1.3 +/- 0.7 to 1.9 +/- 0.9 mL (100 mL)(-1) (RM ANOVA; P = 0.006). The optimal filling condition of the water-pad depended on the water-pad size, while body height was the best predictive value for the water-pad size (Pearson's R = 0.72, P < 0.001).
Conclusion: The filled water-pad markedly increased the venous ejection fraction and volume of the lower leg during stepping, hereby counteracting stasis of venous blood in the immobilized lower leg. Therefore, the water-pad seems to be a promising tool to prevent deep venous thrombosis during periods of lower leg immobilization.