Clinical evaluation of higher stimulation rates in the nucleus research platform 8 system.

OBJECTIVE: The effect on speech perception of using higher stimulation rates than the 14.4 kHz available in the Nucleus 24 cochlear implant system was investigated. The study used the Nucleus Research Platform 8 (RP8) system, comprising the CI24RE receiver-stimulator with the Contour electrode array, the L34SP body-worn research speech processor, and the Nucleus Programming Environment (NPE) fitting and Neural Response Telemetry (NRT) software. This system enabled clinical investigation of higher stimulation rates before an implementation in the Freedom cochlear implant system commercially released by Cochlear Limited. DESIGN: Use of higher stimulation rates in the ACE coding strategy was assessed in 15 adult subjects. An ABAB experimental design was used to control for order effects. Program A used a total stimulation rate of between 12 kHz and 14.4 kHz. This program was used for at least the first 3 mo after initial device activation. After evaluation with this program, each subject was provided with two different higher stimulation rate programs: one with a total stimulation rate of 24 kHz and the other with a total stimulation rate of 32 kHz. After a 6-week period of familiarization, each subject identified his/her preferred higher rate program (program B), and this was used for the evaluation. Subjects then repeated their use of program A for 3 wk, then program B for 3 wk, before the second evaluation with each. Speech perception was evaluated by using CNC open-set monosyllabic words presented in quiet and CUNY open-set sentences presented in noise. Preference for stimulation rate program was assessed via a subjective questionnaire. Threshold (T)- and Comfortable (C)-levels, as well as subjective reports of tinnitus, were monitored for each subject throughout the study to determine whether there were any changes that might be associated with the use of higher stimulation rates. RESULTS: No significant mean differences in speech perception results were found for the group between the two programs for tests in either quiet or noise. Analysis of individual subject data showed that five subjects had significant benefit from use of program B for tests administered in quiet and for tests administered in noise. However, only two of these subjects showed benefit in both test conditions. One subject showed significant benefit from use of program A when tested in quiet, whereas another showed benefit with this program in noise. Each subject's preferred program varied. Five subjects reported a preference for program A, eight subjects reported a preference for program B and two reported no overall preference. Preference between the different stimulation rates provided within program B also varied, with 10 subjects preferring 24 kHz and five preferring 32 kHz total stimulation rates. A significant increase in T-levels from baseline measures was observed after three weeks of initial experience with program B, however there was no difference between the baseline levels and those obtained after five weeks of use. No significant change in C-levels was found over the monitoring period. No long-term changes in tinnitus that could be associated with the use of the higher stimulation rates were reported by any of the subjects. CONCLUSIONS: The use of higher stimulation rates may provide benefit to some but not all cochlear implant recipients. It is important to optimize the stimulation rate for an individual to ensure maximal benefit. The absence of any changes in T- and C-levels or in tinnitus suggests that higher stimulation rates are safe for clinical use.

Evaluation of streamlined programming procedures for the Nucleus cochlear implant with the Contour electrode array.

OBJECTIVE: The objective of this study was to evaluate streamlined programming procedures for the Nucleus cochlear implant system with the Contour electrode array. DESIGN: Phase 1 involved an examination of the clinical MAPs for the first 103 recipients implanted with the Contour electrode array in the Melbourne Cochlear Implant Clinic, to examine the ability to predict the entire MAP based on a smaller number of clinically determined T- and/or C-levels. In phase 2, a subset of the streamlined procedures was selected and clinically evaluated, using speech perception and subjective preference measures. In the first study, the clinical MAP was compared with a MAP based on interpolating across three behavioral T-levels and three behavioral C-levels in a group of newly implanted subjects. The second study investigated the use of a single interpolated profile as the basis to creating the entire MAP. Initial evaluation compared the clinical MAP with two streamlined MAPs, one in which the C-level profile was derived from interpolation across a subset of T-levels and one in which the T-level profile was derived from interpolation across a subset of C-levels. In this case, the interpolated profile was based on five behavioral measures. Subsequently, the use of either three or a single T-level measure as the basis for the interpolated T-level profile was evaluated. Eighteen subjects, who were experienced with the clinical MAP before enrollment in the study, participated in the initial evaluation. The subjects were selected to include a group whose RMS deviation from clinical MAP levels, as determined in Phase 1, was greater than that of the wider population. RESULTS: The Phase 1 analysis showed that as expected, larger differences were observed between the clinical and derived MAP levels as interpolation was applied across fewer measured electrodes and that the use of a single interpolated profile to create the entire MAP resulted in the greatest deviation. No significant group mean difference was found in speech perception scores for newly implanted subjects when mapped with the clinical versus the streamlined MAP based on three behavioral T- and three behavioral C-level measures. For some individual subjects, scores were higher with the streamlined MAP. Subjective reports from the comparative performance questionnaire were consistent with these findings. No significant group mean difference in speech perception scores was found in comparing the clinical MAP with the streamlined MAPs based on a single interpolated T- or C-level profile created from five behavioral measures. Individual effects were observed; however, there was no consistent finding across subjects. The use of three rather than five behavioral T-level measures in the procedure did not result in significantly lower group mean scores; however, significantly poorer scores were obtained for three of the 10 individual subjects. The use of a MAP based on a single behavioral measure did result in poorer speech perception scores when compared with the MAP based on five behavioral T-level measures. These findings were consistent with subjective results from the performance questionnaires administered to determine preference for program across a range of listening situations. CONCLUSIONS: Two streamlined programming procedures are recommended for use in the clinical setting: (1) interpolating across three measured T-levels and three measured C-levels and (2) interpolating across five measured T- or C-levels and using the interpolated profile for fitting of the alternative profile.