Venous filling and elastance in the calf positioned above and below heart level.

INTRODUCTION

Limb venous compliance is a major factor in determining the extent of blood pooling during orthostatic stress. We measured the filling of the calf and of its major veins at different postures and quantified the venous contribution to the total volume shift of the calf. The results were also used to determine the venous elastance and to gain some information on the filling of the small veins.

METHODS

Twelve healthy volunteers participated in the study. The calf volume was measured with strain gauge plethysmography and the veins were imaged with ultrasound in the following positions: supine, sitting with both legs horizontal, sitting with one leg suspended, and supine with one leg raised. Cross-sectional areas of the imaged veins were calculated from the measured diameters. Hydrostatic change in the venous pressure was assumed when calculating the venous elastance.

RESULTS

The maximal increase in the calf area was up to 1 cm2. The large veins accounted for approximately 30% of the total volume shift of the calf except in cases where the subjects had one leg suspended. Then, the contribution of the large veins was less than 20%. The estimated elastance of the large veins was 80 +/- 14 mmHg, which may be regarded as substantial.

CONCLUSIONS

The study suggests that there is a distinct difference in the filling of the small and the large leg veins. The small veins may be the principal contributors to the total compliance of the calf when the venous pressure is above 30 mmHg.