Metrological characterization of a combined bio-impedance plethysmograph and spectrometer

In this paper, the design and characterization of a device, able to analyze the electrical bio-impedance in the frequency domain and its variations with time, is presented. The whole system design, that employs a tetra-polar electrode configuration, a specifically developed printed circuit board, and a data acquisition card connected to a PC, is presented. The measurement system is controlled through LabVIEW virtual instruments. Different reference resistors and RC networks, with impedance values lying in the physiological range of bio-impedances, have been used for assessing the systematic and random uncertainty contributions, and to derive the calibration curves necessary to correct the systematic effects of the developed instrument. The obtained results show that it is possible to achieve excellent metrological performances with the proposed system, that is suitable to be developed in a low-cost and portable version. Two possible applications of the instrument are shown, i.e. cardio-respiratory activity monitoring and bioelectrical impedance spectroscopy.