Factors affecting the in vivo precision of bioelectrical impedance analysis.

The influence of factors which affect the in vivo precision of bioelectrical impedance measurements was investigated in two young female volunteers. Measured impedance increased consistently with time with the subject lying supine, although the effect could be eliminated by rising between measurements. Electrode placement had a relatively large effect, while moving the electrodes such that the volume of conducting tissue was reduced caused the impedance to decrease. Cleaning the skin with alcohol, moving the arm away from the body, and eating a large meal caused impedance to increase systematically. However, drinking a litre of water and varying the depth of respiration had no observable effect.