Correlation between NRT measurement and behavioural levels in patients with the Nucleus 24 cochlear implant

Aim of this study was to determine the relationship between the electrically evoked whole nerve action potential (EAP) and T- and C-level for subjects using the Nucleus 24 cochlear implant system. EAP thresholds were measured using the Neural Response Telemetry system of the Nucleus 24 device. Twelve Nucleus 24 cochlear implant users took part in this study. EAP thresholds were compared with the behavioural measures of T- and C-levels used to programme the speech processor. The EAP and the T- and C-levels were obtained, on the same day, 1 month after cochlear implant activation. EAP thresholds were seen to fall between the T- and C-level. On average, EAP thresholds fell at 72% of the map dynamic range. The majority of absent answers were found in three of the 12 patients, and out of a total of 195 activated electrodes an EAP was recorded in 169. These data show that Neural Response Telemetry is a valuable clinical tool in the Nucleus cochlear implant system, providing information concerning integrity of the implant and status of the peripheral auditory nerves.