A Venous Hemodynamic Model and Measurement of Venous Reflux in the Lower Limb During Walking-Proof of Concept.

Abstract

Objective: Air-plethysmography (APG) is an established plethysmographic method of measuring leg volume changes in absolute units (ml or ml/s) during tiptoeing. However, tiptoe movements use different muscles from walking and the question of how physiological APG measurements during tiptoeing are has never been answered. The recent development of a commercially available wireless APG enables one to obtain measurements during walking. The aim of our pilot study was (a) to validate a venous hemodynamic model of blood volume changes in the leg during walking and (b) determine the magnitude of reflux per step in patients with venous reflux using this model.

Methods: A total of 20 limbs were included into the study. Ten patients with 10 limbs that had axial reflux in the deep veins on duplex scanning without any outflow obstruction or residual thrombosis on venography were selected. Standard measurements were initially made using tiptoeing as the form of exercise. Venous volume measurements made when walking was the exercise were volume on standing (V₀) in ml, volume at steady state when walking (Vss) in ml, residual volume fraction during steady state (RVFss) as a percentage, ejection fraction (EF) as a percentage and inflow into the leg (I) which included reflux and arterial inflow in ml/step.

Results: There was an exponential reduction in volume during the first 7-9 steps indicating a constant EF and supported the assumptions for the volume hemodynamic model. V0, EF and I were higher in limbs with reflux compared with limbs without reflux by 67% (P < 0.007), 44% (P = 0.009) and 156% (P < 0.001) respectively.

Conclusions: The results of this pilot study indicate that the model and method used provide a practical noninvasive method of measuring reflux during walking. The increase in V₀ and EF indicates a compensatory mechanism. This is the first time such a measurement has been possible because of the availability of wireless air-plethysmography. It offers an opportunity for further studies to answer questions such as what the effect of iliac stenting or valvuloplasty are on reflux during walking.