Water-plethysmography or optical volumetry ?

Objective and precise methods are necessary for early, noninvasive detection of chronic venous insufficiency (CVI). Slight oedema of the legs usually are one of the first objective signs of venous diseases. Several techniques of foot volumetry have been described in the literature. In order to get a precise and reliable method for quantifying therapeutic effects in patients with CVI, we constructed a new water-plethysmograph based on the displacement of water (Archimedes' principle). The aim of the present study was to evaluate the reproducibility of measurement of this device, and to compare it with a commercially available optical volumeter. The precision of the two devices was assessed with a waterproof artificial leg of constant volume in order to exclude a possible influence of biological variations in volume. Performing several series of 20 consecutive measurements with both devices, we evaluated a standardized procedure to optimize the precision of the two methods. In repeated measurements, we found a CV (coefficient of variation) of 0.27% for the optical volumeter, whereas a CV of 0.18% was observed for the water-plethysmograph. Measurements of the volume of a human leg showed similar results, but the two CVs were slightly higher due to the biological variation of leg volume. In conclusion, the results suggest that measurements both with the water-plethysmograph and the optical volumeter are highly reproducible and can detect even small changes in leg volume.