Purpose: Venous hemodynamics evaluated during walking better reflect changes that occur under active physiologic conditions than do conventional static modes of exercise such as tip-toe exercise, knee bending, or dorsiflexion. We prospectively studied the efficacy of air-plethysmography (APG) in monitoring venous hemodynamics during ambulation, and with this method we determined the hemodynamic effects of graduated elastic compression stockings on the lower limb during walking at various speeds.
Methods: The residual volume fraction (RVF%) during treadmill walking was monitored with APG in 10 limbs with primary chronic venous insufficiency (CVI)(CEAP(2-4)) at four speeds (1.0, 1.5, 2.0 and 2.5 km/h consecutively), with and without elastic compression (21 mm Hg at the ankle). The method was validated in comparison with standard APG, which is based on tip-toe exercise. RVF obtained during treadmill walking at 1.5 km/h was correlated with RVF measured with standard APG in 30 subjects: 12 healthy volunteers, 11 patients with primary CVI, and 7 postthrombotic limbs. Data were analyzed with nonparametric statistics.
Results: RVF measurements during walking were reproduced with an intra-day coefficient of variation of 5.1% to 16.5%. RVF during walking correlated well with RVF during standard APG (tip-toe) (r = 0.5, P =.004). At each of the investigated walking speeds, stockings improved venous hemodynamics by decreasing RVF, from a median of 50.5% without stockings to 40.5% with stockings at 1.0 km/h (19.8% decrease), from 49% to 39.5% at 1.5 km/h (19.4% decrease), from 50.5% to 41% at 2.0 km/h (18.8% decrease), and from 53% to 45.5% at 2.5 km/h (14.2% decrease) (all speeds, P <.02). Efficacy of the stockings in decreasing RVF (percent change in RVF) was similar across the spectrum of examined speeds (P =.47). During walking with elastic stockings, nominal RVF values were also similar across the spectrum of walking speeds, except at 2.5 km/h (P =.012). During walking without stockings, RVF did not change with treadmill speed, nor did it differ from that obtained with conventional APG (tip-toe) (P =.46). The percentage decrease in RVF generated with elastic stockings correlated with the venous filling index (r = 0.73, P =.017) at 1.0 km/h.
Conclusions: APG is a reproducible and valid method for monitoring venous hemodynamics during walking. Graduated elastic compression stockings significantly improved venous hemodynamics by reducing RVF in limbs with primary CVI at all examined walking speeds (1.0 to 2.5 km/h). The effect was linearly correlated with the amount of reflux (1.0 km/h). The modified application of APG during walking offers a new noninvasive method for assessment of venous hemodynamics in limbs with CVI, enabling quantification of the actual effect of elastic compression therapy during ambulation.