Normative findings of electrically evoked compound action potential measurements using the neural response telemetry of the Nucleus CI24M cochlear implant system.

One hundred and forty-seven adult recipients of the Nucleus 24 cochlear implant system, from 13 different European countries, were tested using neural response telemetry to measure the electrically evoked compound action potential (ECAP), according to a standardised postoperative measurement procedure. Recordings were obtained in 96% of these subjects with this standardised procedure. The group results are presented in terms of peak amplitude and latency, slope of the amplitude growth function and ECAP threshold. The effects of aetiological factors and the duration of deafness on the ECAP were also studied. While large intersubject variability and intrasubject variability (across electrodes) were found, results fell within a consistent pattern and a normative range of peak amplitudes and latencies was established. The aetiological factors had little effect on the ECAP characteristics. However, age affected ECAP amplitude and slope of the amplitude growth function significantly; i.e., the amplitude is higher in the lowest age category (15-30 years). Principal component analysis of the ECAP thresholds shows that the thresholds across 5 electrodes can be described by two factors accounting for 92% of the total variance. The two factors represent the overall level of the threshold profiles ('shift') and their slopes across the electrode array ('tilt'). Correlation between these two factors and the same factors describing the T- and C-levels appeared to be moderate, in the range of 0.5-0.6.

Comparison of two cochlear implant speech processors in better versus poorer performers.

The performance and subjective preferences for two different speech-processing strategies, the Speak strategy in the Cochlear Spectra 22 speech processor and the Multipeak (Mpeak) strategy in the Mini Speech Processor (MSP), are compared within two adult patient groups. Ten experienced cochlear implant (CI) users were selected for this study. One group of 5 CI users have significant open-set speech recognition, and the second group consisted of experienced CI users who have little or no open-set speech recognition on standardized tests (< 30% on sentence tests; < 10% on monosyllabic word tests). While only 4 of the 5 users in each group were available to complete this evaluation, suitable comparisons on the Speak and Mpeak strategies on test performance were possible within each patient group. The performance tests were necessarily different to suit each patient group; however, general trends of test scores and subjective evaluations of each speech processor are compared between these two groups. While the performance scores and subjective ratings consistently favored the Speak strategy in the first group of users, with good open-set speech recognition, the results within the second group were more variable. These findings have significant implications for individual patient and processor selection.

A comparison of neonatal evoked otoacoustic emissions obtained using two types of apparatus.

The transient evoked otoacoustic emission (TEOAE), generated by a click and recorded in the ear canal is influenced by many factors. Of these, the form of the stimulus, the characteristics of the microphone, amplifiers and filter are probably the major ones. In addition, the acoustical loading of the ear canal by the probe may interact with the TEOAE measurement. Data presented here were obtained from 64 babies tested on each of 3 days post partum. The differences in the TEOAEs produced by the ILO88 and POEMS instruments can be quite marked. The ILO88 TEOAEs consistently have larger high frequency components than do the emissions from the POEMS system. The ILO88 system also gives higher correlations between repeat recordings. Such differences point out the need for explicit standards in probe design.

External- and middle-ear factors affecting evoked otoacoustic emissions in neonates.

Babies without any of the known risk factors for hearing impairment were taken from normal maternity wards and tested daily for 3 days post-partum. Tympanometric and evoked otoacoustic emission data were obtained from 121 babies. Middle-ear pressure and middle-ear compliance values were obtained with a Grason Stadler Middle-Ear Analyser (GSI-33) using a 1000-Hz probe tone. All babies had their evoked emissions measured on the Programmable Otoacoustic Emissions Measurement System (POEMS) equipment. The middle-ear compliance, the proportion of normally shaped tympanograms, the middle-ear pressure and the proportion passing EOAE testing all improved over the 3 days. However, the statistically significant factors affecting the pass rate appeared to be only the middle-ear pressure (for a small number of babies) and the degree of obstruction of the external ear canal. Whilst both these factors play a part in determining emission pass/fail rates they do not fully account for the observed changes in pass rate. There are developmental and other mechanisms which must contribute to the increase in pass rate as the baby matures.