Electrical impedance of the cochlear implant lubricants hyaluronic acid, oxycellulose, and glycerin.

Hyaluronic acid (Healon), oxycellulose (hydroxypropyl methylcellulose), and glycerin are lubricants used in cochlear implant surgery for atraumatic deep insertion of the electrode array into the scala tympani. The electrical impedances of these three lubricants were measured to assess possible effects on intraoperative evoked response measurements, such as the electrically evoked stapedius reflex and auditory brain stem response. The impedances of hyaluronic acid, oxycellulose, and saline were very similar and independent of frequency (20 Hz to 1 MHz). Glycerin had an excessively high impedance at low frequencies. A film of hyaluronic acid or oxycellulose around the electrode array immersed in saline did not have any measurable effect on the impedance; a film of glycerin resulted in a strongly reactive polarized layer. However, neither the far-field current spread nor the impedance between stimulated electrodes was affected by any of the lubricants applied as a thin film. This suggests that none of these lubricants affect intraoperative responses, when applied as a thin film.

Detection of the binaural interaction component in the auditory brainstem response.

In humans, the binaural interaction at the brainstem level has been studied for over 15 years. The binaural interaction component (BIC) is obtained by subtracting the summed auditory brainstem response (ABR) in the monaural stimulus mode from the ABR obtained in the binaural stimulus mode. By nature of this subtraction process, the signal-to-noise ratio of the difference waveform is poor, requiring an objective detection criterion to decide whether a significant BIC is present. In this study, the effectiveness of two analysis methods was compared. The first method is the "3 SD' method, which is based on a signal-to-noise evaluation. The second method is a template matching method, in which templates are derived from normal hearing subjects' responses and individual responses are cross-correlated with these templates. The templates were allowed to shift over a range of -0.8 to 0.8 ms in search of the maximum correlation coefficient. Thirty-nine subjects with normal hearing and five patients with a unilateral profound hearing loss participated in the study. ABRs were obtained with rarefaction and condensation clicks at a rate of 15/s and a level of 70 dB nHL. Latencies of the ABR waves I, III and V for all normal hearing subjects and for the normal ear of the patients were within the normal range. The efficiencies of both methods, defined as the number of normal hearing adults with a significant BIC plus the number of patients without a significant BIC divided by the total number of subjects, were determined. The results show that the "3 SD' method is superior to the template matching method: the efficiencies were 95% and 70% respectively, when responses to rarefaction and condensation clicks were taken together. With the "3 SD' method, a significant BIC is demonstrated in almost all normal hearing subjects (97%). However, the "3 SD' method also falsely indicated a significant BIC in one patient. These results suggest that the BIC may have clinical value in studying binaural interaction in humans.

Air-bone gap in patients with X-linked stapes gusher syndrome.

It is often possible to elicit the stapedius reflex in patients suffering from recessive X-linked progressive mixed deafness syndrome with stapes gusher. The presence of an air-bone gap in the audiogram and the ability to elicit the stapedius reflex are conflicting. Measurements were performed on two patients who were suffering from this syndrome, to establish whether the hearing loss was of the mixed or purely sensorineural type. It was argued that, owing to congenital malformations, the audiovestibular system might act as a more than normally efficient transducer, to convert skull vibrations into inner ear fluid motions, leading to bone conduction thresholds that are better than expected. The results of tone and speech audiometry, stapedius reflex measurements, and brainstem evoked response audiometry in this study showed a pattern similar to that generally seen in patients with purely sensorineural hearing loss. This supports the hypothesis that the air-bone gap in the audiogram does not have the usual significance of a conductive hearing loss component.

The Usher syndrome type 2A: clinical findings in obligate carriers.

Ten obligate carriers of Usher syndrome type 2A from 5 different families with 2 affected persons all underwent audiologic, vestibular and ophthalmologic examinations. They had a sensorineural hearing loss which was in excess of that expected for their age at all of the frequencies (0.25-8 kHz) tested, however, only a 10 dB (average) excess in hearing loss at 0.25-0.5 kHz proved to be significant. The speech discrimination scores obtained conformed with the hearing thresholds. Tympanometry, acoustic reflex and brain stem auditory-evoked potential findings were generally normal. Some vestibular abnormalities were found in a minority of the carrier sample, but not beyond the level of false positivity. Ophthalmologic findings were essentially normal, although in 5 carriers there was a subnormal electrooculography (EOG). These findings are not sufficient specific for carrier detection.

Hearing aid fitting of preschool and primary school children. An evaluation using the insertion gain measurement.

This report presents the results of a group comparison between insertion gain measurements and the calculated Articulation Index (AI) in preschool children (n = 35), primary school children (n = 60) and adults (n = 40). Only patients with bilateral sensorineural hearing loss, successfully fitted binaurally with hearing aids, were included. Patients with an asymmetrical hearing loss or an abrupt high frequency loss were excluded. No statistically significant differences were found between the group results of the preschool children and the primary school children. The results showed that the overall level of insertion gain was 7 dB higher in the total children group (primary school and preschool children) than in the adult group and the AI was approximately 0.1 higher in the children group. Additionally, the measured insertion gain was compared to the desired gain resulting from prescriptive rules: it is concluded that for children the so-called half gain rule is appropriate, while for the adults the measured insertion gain lies between the values prescribed by the half gain rule and the one-third gain rule.

X-linked progressive mixed deafness with perilymphatic gusher during stapes surgery.

Stapes gusher is a rare and usually unexpected complication of stapes surgery. This complication will inevitably be encountered during stapes surgery in all affected males with the X-linked, progressive mixed deafness syndrome. The opportunity of studying eight affected males in a large Dutch family with audiometry, vestibulometry, and polytomography was used to identify specific features. Awareness of these features will assist the otologist in recognizing new cases preoperatively.

Perilymphatic gusher and stapes surgery. A predictable complication?

The cases of 3 patients who had 'perilymph gushers' following stapes surgery are reported. The similarities in their clinical histories and examinations are discussed. All 3 were males and had progressive mixed deafness presenting in early childhood. Polytomography revealed anomalies in both the vestibule and internal auditory meatus in 1 patient; the stapedial reflex was unexpectedly large in all 3. Further preoperative evaluation of these features in other patients and patients affected by the X-linked deafness syndrome is indicated in order to assess the validity of the above criteria.

Peripheral and central myelinopathy in Cockayne's syndrome. Report of 3 siblings.

Three siblings with Cockayne's syndrome are reported. Sural nerve biopsies revealed segmental de- and remyelination with onion-bulb formation. Disturbed visual and brain-stem auditory evoked responses indicated demyelination of the central nervous system. The peripheral and central myelinopathy increased with age, suggesting a progressive disorder. Our observations support the theory of Cockayne's syndrome being a leukodystrophy.