Impact of modulating phase duration on electrically evoked auditory brainstem responses obtained during cochlear implantation.

Objective To investigate the effect of increasing phase duration (pulse width, T-pulse) using a biphasic pulse composed of an initial anodic active phase followed by a balancing cathodic phase on the electrically evoked auditory brainstem responses (eABRs) recorded at the time of cochlear implantation. Design eABRs recorded during 188 surgeries for cochlear implantation from 1999 to 2006 in a single center were retrospectively reviewed by two independent observers. All patients were fitted with a NEURELEC cochlear implant (CI) device, initially DIGISONIC(®) then DIGISONIC SP(®) (2004-2006). Result Immediately following cochlear implantation, stimulation by the CI resulted in reliable wave III and V eABR waveforms (mean wave III latency 2.23 ± 0.38 ms SD and wave V latency 4.28 ± 0.42 ms SD). Latencies followed an apical to basal gradient (0.32 ms increase in mean eV latency and 0.12 ms for eIII latency). With increasing phase duration, wave III and wave V latencies significantly decreased in association with a shortening of the eIII-eV interwave gap, while amplitudes of both waves increased. Conclusion The impact of increasing phase duration on latency and amplitude of brainstem responses in a large set of patients implanted with NEURELEC CIs was reported.

Dexamethasone eluting electrodes for cochlear implantation: Effect on residual hearing.

OBJECTIVE: The aim of this study was to compare a cochlear implant electrode array loaded with dexamethasone (DXM) with a conventional passive electrode array for the preservation of residual hearing in gerbils. METHODS: Thirty Mongolian gerbils (Meriones unguiculatus) were implanted with an eluting electrode loaded with DXM (1 and 10%) on one side and a conventional passive electrode on the other side. Hearing thresholds were determined by tone bursts auditory brainstem responses at 4-6 weeks post-implantation and 1-year post-implantation for older gerbils. RESULTS: After 4-6 weeks post-implantation, residual hearing was statistically more preserved with electrode arrays loaded with DXM, regardless of concentration, for the frequencies 16 000 Hz (P = 0.0008), 4000 Hz (P = 0.0038), 1000 Hz (P = 0.0349), and 500 Hz (P = 0.0030). After 1 year, the difference in favor of the DXM+ electrode array was found statistically significant only for the frequency 16 000 Hz (P = 0.0103) but against it for the frequencies 1000 Hz (P = 0.0368) and 500 Hz (P = 0.0010). CONCLUSION: Electrode array with prolonged release of DXM improved short-term preservation of residual hearing after implantation for the frequencies 500, 1000, 4000, and 16 000 Hz in gerbils. The long-term results at 1 year confirmed these data for higher frequencies, but must be verified for the lower frequencies of 500 and 1000 Hz.