Changes over time in electrical stimulation levels and electrode impedance values in children using the Nucleus 24M cochlear implant

Objective: The present study was designed to evaluate changes in psycho-electric parameters, i.e. threshold levels, comfortable levels, dynamic range, and electrode impedance values during the 1st year post-implantation, in children using the Nucleus 24M cochlear implant system. Methods: The maps of 25 pre-lingual children programmed with ACE strategy in Monopolar 1+2 mode were examined at five time points: connection, 1, 3, 6, and 12 months post-initial stimulation. Maps and electrode impedance values were analyzed according to three cochlear segments: basal, medial, and apical. Results: Significant elevations of thresholds, comfortable levels, and dynamic range were found during the first few months of implant use. Specifically, threshold increased and dynamic range widened until the 3 months visit, whereas comfortable levels continued to increase until the 6 months visit, thereafter levels stabilized. Electrode impedance values decreased significantly from connection to the 1-month visit thereafter a stabilization of values was evident. In addition, thresholds and comfortable levels were found to be significantly lower in the apical segment, whereas dynamic range and electrode impedance values did not differ among the cochlear segments. Conclusions: Significant changes in psycho-electric parameters and electrode impedance values were evident during the first 6 months of implant use. Given the important role of an optimal map for speech perception, frequent programming sessions during the first few months of implant use are essential.