Lung ventilation monitoring by electrical bioimpedance technique using three different 4-electrode thoracic configurations: Variability of calibration equations

Our research group proposes the use of electrical bioimpedance (BE) technique to monitor the ventilatory pattern. The objective of this study was to obtain a set of calibration equations in a group of males (M:23) and females (F:22) and analyze the variability of their mathematical adjustments (R2). All equations are aimed to adjust the impedance changes (IC) due to ventilation and transform them into a measurable volume signal. The IC were obtained by three 4-electrode configurations, where, the current injection electrodes were placed in different points around the sixth intercostal space and the voltage detection electrodes were placed in different points around the second intercostal space. All impedance determinations were validated by a pneumotachometer (gold-standard). The calibration equations were obtained from a multivariate analysis of the proportionality coefficients of volume and impedance signals; and the anthropometric parameters of each group of volunteers. The obtained results evidenced that just two sets of equations determined by one configuration had a high mathematical adjustment of 66% and 70% in the group of males and females, respectively. From the validation of these equations, errors of 22%±3% and 15%±3% in the group of males and females, respectively, were evidenced. The variability of errors was significant, however, the analysis of differences between them was not. We conclude that the variability of calibration equations depends on the variability of anthropometric parameters and the amplitudes of impedance changes which are determined by the anatomic spots where the electrodes were placed.