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

Abstract

Previously, our research group obtained a set of calibration equations for being used by a device of electrical impedance tomography (EIT) and transform the impedance changes into a measurable volume signal in a group of healthy males. The mathematical adjustment of calibration equations were acceptable for respiration monitoring in clinical environment. For this case, the impedance variations were obtained from a set of EIT images that were reconstructed by an algorithm using a set of impedance matrixes (IEITM). Each element of IEITM depicts a set of impedance changes taken from the main arrangement of 16 electrodes. Now, our main challenge is to replace the EIT image by a 4-electrodes configuration to monitor breathing. For this purpose, we statistically compared the tetrapolar impedance changes obtained from IEITM and the volume determinations obtained by pneumotachometer (gold standard) in order to determine the optimal 4-electrodes configuration. Subsequently, for each configuration a set of 20 calibration equations were obtained. It was also compared those results determined by using EIT image. From the obtained results, it was evidenced that the best configurations were with electrodes 3-4 and 11-12 and the electrodes 4-5 and 12-13. The mean of R 2 of the 20 calibration equations determined by EIT image, the configuration of electrodes 3-4/11-12 and the electrodes 4-5/12-13 were 0.943±0.010, 0.848±0.062 and 0.690±0.122, respectively. The error (%) of volume determinations obtained by EIT, using EIT image, 3-4/11-12 and 4-5/12-13, respect those obtained by pneumotachometer were of 15±6%, 16±4% and 43±41%, respectively. From the statistical comparison of the errors, it is evidenced that volume differences obtained by EIT, using image and configuration of electrodes 3-4/11-12, not showed statistically significant differences. So, we concluded that the EIT image and the configuration 3-4/11-12 are exchangeable. So, it is possible to use this 4 electrodes arrangement for respiration monitoring.