Tetrapolar Low-Cost Systems for Thoracic Impedance Plethysmography

Bioelectrical impedance analysis applied to the pneumographic investigation is a technique for monitoring the breathing activity through the measurement of variations in the trans-thoracic electrical impedance. In this paper we present, a low-cost re-configurable measurement system. The system is based on a 4-electrode voltamperometric technique and a network of inertial sensors for correction of arms motion artifacts. The trans-thoracic impedance is acquired via an ad hoc programmed LabVIEW software. A correction algorithm, based on the correlation between the acquired signal and the motion artifact, is proposed. A preliminary metrological assessment of the system is performed to evaluate the accuracy and sensitivity of 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.