The probability of system failures increases as the number of cochlear implants increases throughout the world. Whether a malfunction is a technical or physiological problem remains to be defined, particularly in very young children, while a psychogenic hearing disorder after implantation must not be excluded in adults. The battery of objective measurements used clinically at the Medizinische Hochschule, Hannover has provided useful diagnostic information for distinguishing possible causes of failure. In a normally functioning device, an electrical signal equivalent to the biphasic rectangular stimulation pulse can be recorded by measuring skin potentials from surface electrodes placed on the mastoid of the implant side and the forehead. The signal from the stimulated implanted electrodes is derived by applying a constant pulse rate. Signal averaging is not necessary. If no signals are observed, a non-functioning device should be suspected. If the device works normally, function of the auditory pathways can be examined by recording the electrically elicited stapedius reflex or electrically evoked brain-stem responses. In our experience with more than 450 cochlear implant patients, eight internal device failures occurred, while an additional three patients had either reduced or no hearing sensations due to a disorder of the auditory pathways.

Acoustic Stimulation↗

PubMed1994

[Effect of anesthesia on the intraoperative elicited stapedius reflex].

Evaluation of the intraoperative electrically evoked stapedius reflexes during cochlear implant surgery has two purposes: (1) The functioning of the device and the peripheral auditory pathways can be proven immediately and (2) The data of reflex threshold can be used for the prediction of later threshold (T)- and maximum comfortable (C) levels. This is especially useful for the later fitting of the speech processor in very young children. When trying to use the stapedius reflex data for the prediction of T- and C-levels it must be considered that during surgery the drugs used for general anaesthesia influence the values of the stapedius reflex. Depending on the drug, the stapedius reflex threshold can be increased or the reflex can even be totally blocked. This is not only due to relaxants but also to anaesthetics. To investigate this influence we first determined the acoustically evoked stapedius reflex threshold in normal hearing adults under general anaesthesia with 7 different anaesthetics without additional relaxation. It was found that especially with Dormicum and Brevimytal the stapedius threshold increased only very lightly or did not change at all. In a second investigation the electrically evoked stapedius reflex thresholds were obtained in adults who underwent a cochlear implant surgery using the same anaesthetics for anaesthesia. The intraoperatively evaluated reflex data were compared with postoperatively obtained data. It was found that both reflex thresholds were similar if evaluated in Dormicum or Brevimytal anaesthesia. This suggests that only with the use of the right anaesthetics the data of the electrically evoked stapedius reflex obtained intraoperatively can be used for predicting T- and C-levels.

Anesthesia, General↗

PubMed1993

A study of monopolar and bipolar stimulation modes with a modified Nucleus Mini-22 cochlear implant.

Explore the source record for details and available documents.

Cochlear Implants↗

PubMed1993

Stimulus-inadequate sensations in cochlear implant patients.

From August 1984 to April 1987 the Department of Otolaryngology at the Medizinische Hochschule in Hannover implanted the NUCLEUS 22 channel cochlear implant system (CI) in their first 56 adults. Since implantation, 27 (51%) patients have described undesirable sensations from their implant. These were defined as stimulus-inadequate sensations (SIS) and were classified into three types: 1) pain-like sensations; 2) high-frequency sensations; and 3) non-stimulation. Twenty-three patients were radiographically investigated by polytomography. All of the intracochlear electrodes were visualised and a correlation between SIS and the radiological findings was established. It was found that i) SIS similar to pain are caused by electrical stimulation of the mucous membranes and periosteum of the tympanic cavity; ii) the high-frequency SIS seemed to be due to non-physiological electrical stimulation of the basal ganglion cells; and iii) the reason for non-stimulation is probably damaged electrodes and fibrosis around the electrode. Conventional tomography is the method of choice for estimating the number and configuration of intracochlear electrodes.

Adolescent↗

PubMed1992

Experience with the cochlear miniature speech processor in adults and children together with a comparison of unipolar and bipolar modes.

Following the experience with nearly 150 patients with the Nucleus cochlear implant, a more sophisticated and lighter speech processor was tested successfully in terms of better speech understanding. In order to prepare further miniaturization, the standard bipolar stimulation mode was compared with an unipolar mode. It was found that unipolar stimulation needs less energy, without decreasing speech understanding. Preconditions for supplying very young children with a cochlear implant were the use of electrically elicited stapedius reflex thresholds, obtained intraoperatively, for the fitting of the speech processor and the setup of a special rehabilitation center, where children together with their mothers could be trained in hearing and understanding by special teachers and engineers for 12 weeks, distributed over the 1st postoperative year.

Adult↗

PubMed1992

[Correlation between electrically-induced stapedius reflex and discomfort threshold in cochlear implant patients].

Electrically elicited stapedius reflex thresholds are an objective criteria for the fitting of speech processors in very young children. Reflex thresholds generally fit well within the upper third of a subject's individual dynamic range, the difference between electrical threshold of hearing, (T) and maximum comfort (C) levels and can be used to predict ultimate behavioral maximum comfort levels. In acoustically elicited stapedius reflexes a saturation of impedance amplitude can be registered at approximately 110 dB, which is 90% of the dynamic range. Assuming a similar relationship for the electrically elicited stapedius reflex there would be two values within the dynamic range which could be used for extrapolation of the threshold level. In the present study, the electrically elicited stapedius reflex was examined in 16 deaf patients who had received 22-channel Clark/NUCLEUS cochlear implants. Using an apical, a medial and a basal electrode pair, different stimulation positions within the cochlea were tested. The contralateral reflexes could be elicited in 11 patients (69%). A saturation of the reflex amplitude was recordable in 10 subjects, at least in one of the electrode pairs. The reflex saturation in all cases was located close to the uncomfortable loudness level within the subjects' dynamic ranges (at 95% dynamic). This finding is comparable to acoustic matter. As a result, these data together with reflex threshold data suggest a means for predicting to predict the threshold levels.

Acoustic Impedance Tests↗

PubMed1991

Comparative speech recognition results in eight subjects using two different coding strategies with the Nucleus 22 channel cochlear implant.

This study was designed to compare the results of several speech tests administered to eight subjects who used two types of speech-coding strategies with the Nucleus 22 channel cochlear implant. The subjects had an average experience of 40 months with the F0F1F2 coding strategy implemented in their previous wearable speech processor. Three subjects were good performers (showing significant open-set understanding without lip-reading) and five were moderate performers (not able to do speech-tracking by auditory means alone). All subjects were evaluated again after 1 month and 6 months of experience with the MULTIPEAK coding strategy of the miniature speech processor. The test materials included vowel and consonant identification, monosyllabic words, everyday sentences and numbers in noise. All eight subjects showed an improvement on more than three of five measures. The group of moderate performers showed a larger improvement in vowel (+16%) and consonant (+17%) identification scores than the group of good performers. For the open-set sentence test, the better patients were able to increase their score from 52% to 80% correct; two of the moderate performers did not improve. Six subjects achieved significantly higher scores at moderate signal-to-noise ratios (up to 10 dB S/N) in the (Freiburger) number test. Results of information transmission analysis are also discussed.

Acoustic Stimulation↗

PubMed1990

Electrically elicited stapedius reflex in cochlear implant patients.

Electrically elicited stapedius reflexes were examined in 25 deaf patients who had received a 22-channel Clark/NUCLEUS cochlear implant. Using an apical, a medial and a basal electrode pair, different stimulation positions within the cochlea and different stimulation modes were examined. For threshold determination, 10 reflexes were averaged with reflexes recorded on the nonoperated side. Reflexes were elicited in 19 of the 25 patients (76%); a saturation of reflex amplitude could be recorded in 14 (56%) subjects. In two additional cases, a reflex could be obtained by increasing the bipolar stimulation width (changing the stimulation mode). In comparison with different stimulation positions within the cochlea, the stimulation of apical electrodes produced more distinctive reflexes and required lower current levels. An increase in the bipolar stimulation width also decreased the intensity required for stapedius reflex threshold. Our data suggest that stapedius reflex evaluation may be a useful tool for speech processor fitting.

Adult↗

PubMed1989

[Suppression of tinnitus by electric stimulation in cochlear implant patients].

The use of electrical stimulation for the treatment of tinnitus was evaluated on 38 cochlear implant patients suffering from chronic tinnitus. In answer to a questionnaire 29 (76%) of the subjects reported a reduction of the tinnitus while using their speech processor; 15 even noted complete suppression. Sixteen patients used a processor delivering subthreshold current for 2 weeks. A placebo trial followed. Reduction of tinnitus was found in only 3 (19%) of the patients; however, 13 (81%) mentioned a substantial decrease of tinnitus when using their own device with above-threshold stimulation. The fact that tinnitus was also reduced on the contralateral side suggests that the acoustic masking effect must be the main determining factor rather than electrical stimulation. Therefore, the best therapy for the deaf seems to be the improvement of their hearing ability.

Adult↗

PubMed1988

[Psychophysical data and speech comprehension after 2 years with the Clark/Nucleus prosthesis].

Psychophysical data such as threshold and comfort levels indicate an extensive preservation of auditory nerve fibers. Changes of these data can point to increasing damage of nerve fibres due to long-term electrical stimulation or to obliteration of the cochlea when an intracochlear system is used. Unfavourable levels indicate negative influence on speech comprehension. The psychophysical data and the speech comprehension of 10 patients fitted with a Clark/NUCLEUS cochlear implant in the last 2 years have been analysed. During this period of time the threshold and comfort levels remained almost stable, whereas speech comprehension is still increasing, though to a lesser extent, after 2 years with the implant. These results indicate that the patients suffer neither an increasing destruction of auditory nerve fibres nor severe intracochlear changes.

Auditory Threshold↗

PubMed1988

[Changes in the hearing and discomfort thresholds in patients with the Clark/nucleus inner ear prosthesis].

The Nucleus 22-electrode cochlear implant should be fitted individually for both pitch and loudness. Loudness is related to the charge delivered, and is usually controlled by current amplitude. In special cases the loudness may be influenced by stimulation mode and pulse width. 3 examples demonstrate optimal fitting with low current intensities, using these possibilities. In addition the threshold level and comfortable level date were analysed over a 2-year period. No significant changes were found, indicating that electrical stimulation caused no damage to the remaining auditory nerve fibres.

Adult↗