Effect of Electrode Design on Impedances in CI Patients
23 April 2019 (online)
The trauma during the insertion of a cochlear implant electrode is thought to trigger soft tissue production that ultimately leads to an increase in impedances over time. Therefore one would expect to see a rise of impedance values in the postoperative period that is more pronounced with thick and traumatic arrays compared to thin and atraumatic ones.
To test this hypothesis we compared the impedance values of the three Nucleus arrays, the slim straight (522), slim modiolar (532) and contour (512) electrodes over time using database readouts of 800 CI patients.
Our results demonstrate a significant increase of impedance values between the postoperative measurement and the first fitting. Between the first fitting and the 3-month-visit there is a sharp decrease to a slightly higher than postoperative level in all arrays. The impedance values for the contour electrode were shown to be significantly higher postoperatively, but not at the first fitting. However there was a significantly larger increase towards the 3-month-visit compared to the “slim” electrodes.
The drop in impedance values after the first fitting is most likely due to the electrical stimulation between the first fitting and the 3-month visit. It is unclear why impedances of the contour electrode are higher from the beginning. A steeper increase of impedance values due to insertion trauma may be inhibited by the administration of intraoperative cortisone. Yet, a significant increase is present for the more traumatic Contour electrode compared to slim electrodes.