Postimplantation changes of electrophysiological parameters in patients with cochlear implants

To evaluate the postoperative changes of the basic electrophysiological and psychophysical parameters in cochlear implant (CI) patients: the impedance of the electrode contacts, the electrically-evoked compound action potential (ECAP) thresholds and the T/C levels.

Retrospective case review in a quaternary otologic referral centre.

Data on the impedance of the electrode contacts, the ECAP thresholds and the T/C levels were collected in 20 consecutive CI patients divided into 2 groups. Group 1 comprised 10 prelingually deaf children implanted before the age of 18 months, and group 2 comprised 10 postlingually deaf adults (average age of 58 years). All patients were users of the Nucleus 24RECA (Freedom, Contour advance off-stylet electrode) CI.

(1) The mid-portion and the apical electrodes showed a decrease in the impedance values between the 1st and the 6th postoperative months and stabilization in the later course. Impedance of the most basal electrodes grew during the first postoperative months and stabilized later on, but remained higher than the impedance of the mid-portion and the apical electrodes. (2) The neural response telemetry threshold values tended to decrease within the first 3 months after surgery to reach a plateau afterwards. (3) The behavioural threshold levels remained generally stable, except for the basal electrodes where a decrease could be observed. The hearing comfort levels showed an increase during the first 6 months of the implant use and remained stable afterwards.