A New Method for Lower Limb Volume Measurement — Laser Plethysmography: Comparison with Two Commonly Used Methods

Abstract

Objective: (1) To assess agreement between laser plethysmography (LPG) and mercury strain-gauge plethysmography (MSGP) measurement of calf volume variation. (2) To assess agreement between LPG and water volumetry measurement of calf volume. Design: Pilot study to evaluate a method of measuring absolute lower leg volume and volume changes in volunteers; randomisation of the leg measured and of the order of measurement, evaluation of between-method correlation and limits of agreement. Setting: Hôpital Civil, Strasbourg. Participants: Seventeen healthy volunteers. Main outcome measures: Measurement of relative volume change by MSGP and LPG before and after venous occlusion by means of a thigh cuff inflated to 20 mmHg (zlV20) and 60 mmHg (/dV60); absolute volume of a 20 cm segment of lower limb measured by differential water plethysmography (two different volume water boots) and by LPG. Results: Comparison of LPG with MSGP led to fairly good correlation coefficients (r = 0.89 and r = 0.91 for δV20 and δV60, respectively) but also to an important dispersion of between-method differences (wide limits of agreement). There was a high degree of agreement between LPG and water volumetry: the correlation coefficient was 0.99 and limits of agreement were [− 6.7% 0.8%] but a significant bias was seen. Conclusions: Laser plethysmography is a new method for measurement of lower limb volume. When tested on inert material, very good accuracy and reproducibility were obtained. Comparison with water volumetry gave good agreement. Evaluation of reproducibility on healthy volunteers is required for complete validation of the device.