Optimizing electrode sites for segmental bioimpedance measurements

Recent advances in the application of bioelectrical impedance analysis (BIA ) have indicated that a more accurate approach to the estimation of total b ody water is to consider the impedance of the various body segments rather than simply that of the whole body. The segmental approach necessitates def ining and locating the physical demarcation between both the trunk and leg and the trunk and arm. Despite the use of anatomical markers, these points of demarcation are difficult to locate with precision between subjects. The re are also technical problems associated with the regional dispersion of t he current distribution from one segment (cylinder) to another of different cross-sectional area. The concept of equipotentials in line with the proxi mal aspects of the upper land lower) limbs along the contralateral limbs wa s investigated and, in particular, the utility of this concept in the measu rement of segmental bioimpedance. The variation of measured segmental imped ance using electrode sites along these equipotentials was less than 2.0% fo r all of the commonly used impedance parameters. This variation is approxim ately equal to that expected from biological variation over the measurement time. It is recommended that the electrode sites, for the measurement of s egmental bioelectrical impedance in humans, described herein are adopted in accordance with the proposals of the NM Technology Assessment Conference S tatement.