Feasibility of long-term monitoring of multi-frequency and multi-segment body impedance by portable devices

Available devices for multisegment bioelectric impedance spectroscopy (BIS) do not allow monitoring the body composition without interfering with the subject's activities. In this study, we evaluated the feasibility of unobtrusive multisegment BIS with small portable devices by presenting and testing a DSP-based prototype specifically designed to minimize weight, size, and power consumption of BIS systems. The prototype consists in 1) a tetrapolar electrodes setup; 2) an analog board with a transconductance amplifier which injects the stimulation current and an instrumentation amplifier which senses the associated voltage drop; and 3) a digital board with a digital signal processor for data processing, for system calibration and for generation of the stimulating waveforms. To optimize the design, the prototype employs square-wave stimulating waveforms, easier to be generated compared to sinusoids. The performances of the prototype were tested by monitoring BIS in the arm, trunk, and leg on a group of 20 volunteers (ten males and ten females) during a 40-min experimental protocol which included postural changes. Results demonstrated the capability of our prototype to follow impedance changes due to the redistribution of fluids after postural changes and to detect gender differences likely associated to the diverse composition and size of body segments in males and females.