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.

Relationship between NRT measurements and behavioral levels in children with the Nucleus 24 cochlear implant may change over time: preliminary report.

OBJECTIVE: Response from spiral ganglion cells to electrical stimulation via the Nucleus 24 cochlear implant can be measured using the neural response telemetry system. The purpose of this study was to assess, in children, the correlation between the neural response threshold and the behavioral levels used for cochlear implant programming process. METHODS: The neural response telemetry test was administered to 23 children (mean age at implantation: 4 years) with the Nucleus 24 cochlear implant. Four intra-cochlear electrodes (electrodes 5, 10, 15 and 20) were tested. The neural response threshold at 3, 6, 9 and 12 months post-implantation was compared with the behavioral threshold and the maximum comfort level estimated during the same periods: a Pearson's correlation test was performed for each tested electrode. RESULTS: On apical electrodes, the correlation with the behavioral threshold remained significant from 3 to 12 months post-implantation (r ranging from 0.696 to 0.909, P<0.05), and the correlation with the maximum comfort level was also significant throughout the study period, except on electrode 15 at 9 months (tendency to significance). On basal and intermediate electrodes, statistical correlations were found only at some points of time; nonetheless, at 12 months post-implantation, a significant correlation with behavioral levels could be clearly demonstrated both on electrode 15 (r=0.914--0.778, P<0.05) and on electrode 10 (r=0.845--0.720, P<0.05). CONCLUSIONS: This preliminary study suggests that the correlation between the neural response threshold and behavioral levels may improve from the base towards the apex of the cochlea. However, a significant correlation can be demonstrated for all tested electrodes at 12 months post-implantation. During the first months post-implantation care must be exercised when interpreting neural response telemetry measurements: a positive test does not necessarily mean that the stimulus delivered to the acoustic nerve will be centrally processed with the result of an auditory perception.

Correlation between electrical auditory brainstem response and perceptual thresholds in Digisonic cochlear implant users.

OBJECTIVES: To examine the relationships between psychophysical perceptions and the electrically evoked auditory brainstem responses (EABRs) in multichannel cochlear implant (CI) users and to determine the effectiveness of EABRs in electrode failure. DESIGN: A descriptive study reported the EABR characteristics while the different electrodes were activated. Characteristics of the EABR and of the perceptual measures served as compared variables in a correlational study. SETTING: The study was carried out in the audiology clinic of an otolaryngology department at a university hospital. PATIENTS: The subjects consisted of nine consecutively selected habitual Digisonic DX1OR multichannel CI users. Seven patients were postlinguistically deafened adult patients; two were congenitally deaf children. MAIN OUTCOME MEASURES: Ipsilateral recordings were performed using a previously published method. Morphology, latency, and amplitude measures of the EABR recordings were described, computed, and compared with the literature data for EABRs obtained while activating other types of CI and for acoustically evoked ABRs. Correlations between EABRs and behavioral perception thresholds were analyzed using the parametric Pearson's correlation test. RESULTS: EABRs allowed the authors to detect failure of no. 10 electrode integrity in one child. Perceptual threshold measures were found to be highly significantly related to the EABR threshold across subjects and electrode position (n = 31, r = 0.98; P < 0.001; linear regression equation: perceptual threshold = 1.06 EABR threshold + 0.76). The latencies and amplitudes were found to be similar to those described in the literature. CONCLUSIONS: EABRs may be used to estimate settings for the Digisonic DX10 CI even in a pediatric population, although they cannot entirely replace behavioral measurements, especially in children. The EABR can be employed for electrode dysfunction diagnosis. Further studies are needed to determine whether recordings of EABR quality could contribute to the evaluation of functional prognosis during the rehabilitation.

[Value of auditory evoked potentials of the brain stem in patients with a Digisonic cochlear implant]. / Intérêt des potentiels évoqués auditifs électriques du tronc cérébral chez les patients porteurs d'un implant cochléaire Digisonic.

We report our techniques of electrically elicited Auditory Brainstem Responses (eABR) in Digisonic DX 10 cochlear implanted patients and summarize the theoretical interests of objectives measures in pre-, per- and post-operative periods of the cochlear implantation process. This report demonstrates the major interest of eABR during rehabilitation with a cochlear implant. EABR allowed us to detect the lack of device integrity in one electrode in one patient. The quality of electrically elicited responses can contribute to appreciate the electrophysiological responses during electrical stimulation. We found a very strong correlation between the objective thresholds (obtained by means of eABR) and subjective ones (obtained by means of behavioral methods); this is of major interest in the pediatric populations.

[Study of the ototoxicity of amikacin and netilmicin using provoked acoustic oto-emissions and high-frequency audiometry]. / Etude de l'ototoxicité de l'amikacine et de la nétilmicine au moyen des oto-émissions acoustiques provoquées et de l'audiométrie hautes fréquences.

To compare the ototoxicity of amikacin and netilmicin, tone audiometry, high-frequency audiometry, early auditory evoked potentials, and evoked otoacoustic emission testing were used to evaluate 30 patients (15 under amikacin and 15 under netilmicin). Ototoxicity was not significantly different in the two groups.

Evoked otoacoustic emissions: correlates between spectrum analysis and audiogram.

Correlations between spectrum analysis of evoked otoacoustic emissions (EOAEs) and hearing losses have been calculated in 150 patients with pure sensorineural hearing loss. Significant correlations were found. The greater the high-frequency spectral components of the EOAE, the better the high-frequency hearing. However the relationship is complex, and it does not seem possible to establish an audiogram knowing only the spectrum analysis of EOAEs.

Variability of the influence of a visual task on the active micromechanical properties of the cochlea.

The effect of a visual task on the active micromechanical properties of the cochlea studied by the evoked otoacoustic emissions (EOAEs) has been the subject of only one published study (Brain Research, 44 (1988) 380-383). In order to examine the reliability of this effect, a similar study has been run on 16 subjects. A significant decrease in EOAEs during a visual task was obtained for 3 subjects. The two subjects whose decrease was the most significant were tested again one month later and the same effect was found. This striking interindividual variability is discussed in terms of olivo-cochlear neuronal excitability.

Validity of bone conduction stimulated ABR, MLR and otoacoustic emissions.

The present study considers the validity of objective auditory investigation via bone conduction. Auditory Brainstem Responses (ABR) and Middle Latency Responses (MLR) were recorded in response to a bone vibrator stimulation with or without continuous bilateral air white noise masking. In all cases, such masking was found to result in an absence of recorded evoked potentials. It shows that under bone-conducted stimulation the evoked potential recorded is purely auditory, with no additional mechanical somatosensory component. In a further study, the feasibility of oto-acoustic emissions (OAEs) via bone conduction is demonstrated. These OAEs are, for a given subject, comparable to those found for air-transmission stimulation.

Are BAEP and MLR suited for the study of a hypothetic peripheral selective attention effect?

BAEPs and MLRs for clicks were recorded for situations of selective attention, ignoring stimuli and mental arithmetic. Certain studies have shown no attention effect on these evoked potentials, but several others have shown reduction of latency and increase in amplitude under selective attention. Our study finds no significant difference in latency or amplitude for BAEP waves I, III and V, nor in Na or Pa latency or NaPa amplitude for MLR. What we know anatomically of cochlear innervation, particularly efferent innervation, would seem to show that efferent projection is basically onto the outer hair cells which have been little if at all explored by BAEPs and MLRs under standard conditions. A study of outer hair cell functioning under various attention situations would be needed in order to find any peripheral selective attention effect.

Effect of stimulus intensity variation on brain-stem auditory evoked potentials: comparison between neonates and adults.

Brain auditory evoked potentials (BAEPs) were recorded from 40 adult subjects and 40 neonates at 80 and 60 dB (nHL) to compare the effects of stimulus intensity variation on waves I, III and V and on intervals I-III, III-V and I-V. The results show that the changes in latency for wave, I, I-III and I-V intervals are significantly greater in neonates than in adults. So the effects of stimulus intensity variation on BAEPs are different in neonates and in adults and a major effect is in the peripheral auditory mechanism.

Psychological factors affecting outcome of treatment after transcutaneous electrotherapy for persistent tinnitus.

We used transcutaneous electrotherapy to treat 27 patients with persistent tinnitus. Each patient was tested with the short form of the Minnesota Multiphasic Personality Index test (MMPI) prior to the commencement of treatment. The "unimproved" group of patients (n = 15) showed higher pretreatment scores for depression (P less than 0.05), psychasthenia (P less than 0.05) and schizophrenia (P less than 0.02). Our findings indicate that patients having significantly pathological scores on at least one of these three scales will fail to benefit from treatment. These findings also show that there appear to be psychological prognostic factors that can be used to evaluate patients receiving transcutaneous electrotherapy for persistent tinnitus.

Control by the evoked potential of the brain stem of the administration of dibekacine in premature infants.

The administration of dibekacine to 10 newborn carriers of a germ infection--or staphylococcus, was controlled for auditory tolerance. The auditory threshold was controlled by the evoked potential of the brain stem. Medication never caused the threshold to change. The evolution of latency in waves J1, J3 and J5 could not be seen except in wave 1 where latency decreased, as can be seen in other premature infants of babies born at term.