A new method for lower limb volume measurement - Laser plethysmography: Comparison with two commonly used methods

Objective: (1) To assess agreement between laser plethysmography (LPG) and mercury strain-gauge plethysmography (MSGP) measurement of calf volume vari ation. (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 vo lume and volume changes in volunteers; randomisation of the leg measured an d of the order of measurement, evaluation of between-method correlation and limits of agreement. Setting: Hopital Civil, Strasbourg. Participants: Seventeen healthy volunteers. Main outcome measures: Measurement of relative volume change by MSGP and LP G before and after venous occlusion by means of a thigh cuff inflated to 20 mmHg (triangle V20) and 60 mmHg (triangle V60); 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 coeffic ients (r = 0.89 and r = 0.91 for Delta V20 and triangle V60, respectively) but also to an important dispersion of between-method differences (wide lim its of agreement). There was a high degree of agreement between LPG and wat er 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 reprodu cibility were obtained. Comparison with water volumetry gave good agreement . Evaluation of reproducibility on healthy volunteers is required for compl ete validation of the device.