Tetrapolar low-cost systems for thoracic impedance plethysmography

Bioelectrical impedance analysis applied to pneumographic investigation is a technique for monitoring the respiratory activity through the measurement of variations in the trans-thoracic electrical impedance. In this paper, a low-cost reconfigurable measurement system is presented. The system is based on a 4-electrode volt-amperometric technique and a network of inertial sensors for correction of arms motion artifacts. The trans-thoracic impedance was acquired via an ad-hoc programmed LabVIEW software. A correction algorithm, based on the correlation between the acquired signal and the motion artifact, was proposed. A preliminary metrological assessment of the system was performed to evaluate the accuracy and sensitivity to patient breath monitoring. Results show a high accuracy in a 100 Ω range of measurement. The proposed algorithm allows for the estimation of the thoracic impedance with a maximum error of 30% and to neglect the phase shift between the breath and the movement signals.