Tidal volume monitoring by a set of tetrapolar impedance measurements selected from the 16-electrodes arrangement used in electrical impedance tomography (EIT) technique. Calibration equations in a group of healthy males

摘要

Previously, our research group obtained a set of calibration equations for being used by an electrical impedance tomograph (EIT). All equations transform the impedance changes into a measurable volume signal in a group of healthy males. The performance of EIT, using these equations, was acceptable for respiration monitoring. The EIT impedance changes were obtained from a set of 16-electrodes placed around the thoracic box at level of the sixth intercostal space. Each cycle of impedance measurements is ordered in a matrix (IEITM). Each IEITM's element depicts a configuration of 4-electrodes. Now, our main challenge is to replace the ELT's 16-electrodes by a 4-electrodes configuration. We analyzed the impedance changes obtained from each element and the volume determinations obtained by a pneumotachometer (gold standard) in order to determine the optimal 4-electrodes configuration. For each selected configuration a set of 20 calibration equations were obtained. The best results were obtained by using two 4-electrodes configurations. Both consisting in two adjacent electrodes for current injection and two electrodes for voltage detection.