Correlations between the electrically evoked action potential (EAP) parameters and the psychophysical measures in pre-lingually deaf implanted patients

Objectives: Pre-lingually deafened adolescents represent a unique population in that EAP parameters can be compared to reliable psychophysical measures in congenital deafness. The aim of this study was to characterize EAP parameters in pre-lingually deafened adolescents receiving a HiResolution Bionic Ear implant with respect to the psychophysical levels used for cochlear implant (CI) fitting. Methods: Fifteen subjects were enrolled in this study (mean age at the time of implantation 16.98.4 years). M levels were set at the most comfortable level while T levels were automatically fixed at 10% of the M levels. EAPs were obtained intra-operatively, at first fitting and at 2 weeks, one month, 3, 6, 9 and 12 months after CI connection at three electrode locations (15, 9 and 3) by utilizing biphasic pulses with 32 ms phase duration presented at 30 Hz with an alternating polarity. Results: Mean EAP thresholds obtained at first fitting and 12 months after CI connection were 18059 and 18958 CU respectively for the apical electrode, 21344 and 19061 CU for the intermediate electrode, and 22571 and 21064 CU for the basal electrode. M levels increased during the first three months and stabilized thereafter. Mean ratio of EAP thresholds to M levels at 12 months were 58, 53 and 61% for the apical, intermediate and basal electrodes. Conclusions: EAP measures were very stable over time and showed low variability among subjects and across electrodes. EAP thresholds could be utilized to set M-levels in pre-lingually deaf patients receiving a HiResolution Bionic Ear implant with an acceptable degree of reliability.