Calculation of the Faradaic Impedance of the Electrode–Tissue Interface Improves Prediction of Behavioral T/C Levels in Cochlear Implant Patients

BACKGROUND: Fitting of cochlear implants is a labor-intensive process, and therefore automated fitting procedures are being sought. The objective of this study was to evaluate if decomposition of the complex impedance of the electrode–tissue interface could provide additional parameters that show improved correlation with the behavioral T/C levels. METHODS: A new method for decomposing the complex impedance of the electrode–tissue interface was developed and tested in 18 patients in a prospective study in a tertiary otologic referral center. RESULTS: The averaged near-field Faradaic resistance (R(F)) calculated in study subjects shows a very strong correlation (R (2) = 0.80) with the behavioral C levels and can be used for automated fitting in most patients. The standard deviation for the T levels and the C levels calculated for each of the electrode contacts in all study subjects is in the range of 10-15 CL and 15-20 CL, respectively. These higher values of the standard deviations are caused by a few outliers who require that additional parameters have to be added to the metric equation, allowing for the automated prediction of the T/C levels. CONCLUSION: A new method for deriving information from the electrode impedance measurements shows excellent correlation of the Faradaic resistance with the behavioral T/C levels in most patients and can be very useful for fitting cochlear implants based on objective measures. Since some patients still show discrepancies between the predicted T/C levels based on the R(F) calculation, additional parameters have to be added to the metric equation, allowing for automated prediction of the T/C levels.