Wrist-wearable bioelectrical impedance analyzer with contact resistance compensation function

Abstract

Bioelectrical impedance analysis (BIA) is used to calculate the body fat percentage of a human by applying a small amount of alternating current through a human body and measuring the impedance. As the electrode size of a BIA device becomes small, the measurement error of impedance becomes large due to the contact resistance between the electrode and human skin. Most commercial BIA devices, therefore, utilize electrodes large enough to ignore the effect of contact resistance, e.g. 35×40 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> × 4EA. We propose a novel method for compensating the contact resistance by performing a 4-point and a 2-point measurement alternately such that body impedance can be accurately estimated even with a considerably smaller size of electrode (8×8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> × 4EA). Also, we report a wrist-wearable BIA device with single-finger contact measurement and analysis results of user data acquired from 148 volunteers: the correlation coefficient of body fat percentage was 0.903 and the SEE (Standard Error of Estimate) of body fat percentage was 3.07% when compared with InBody 720 (whole-body composition analyzer), which was found to be at the same level of performance as commercial portable upper-body BIA device.