Chromosomal localization of a gene responsible for vestibulocochlear defects of BUS/Idr mice: identification as an allele of waltzer.

Mice of the bustling mutant strain BUS/Idr have vestibulocochlear defects. bus/bus homozygotes, but not heterozygotes, are hyperactive and display an abnormal behavior such as circling, head bobbing and head tilting. To characterize BUS mice further, the auditory brain-stem response of the mutant was examined. In +/bus heterozygotes as well as control animals, the auditory brain-stem response was developmentally first recorded as early as 11 days of age and heterozygous and normal adults showed typical auditory brain-stem responses with five peaks in a threshold of 40-45 dB SPL. In contrast, bus/bus homozygotes showed no auditory brain-stem response at any age in response to stimuli up to 130 dB SPL, indicating that they are deaf throughout life. Linkage analysis revealed that the responsible gene, originally designated as bus, maps on chromosome 10, 1.09+/-0.9 cM distal to D10Mit127 and D10Mit59, and 0.72+/-0.51 cM proximal to three markers, D10Mit48, D10Mit112 and D10Mit258, at a site indistinguishable from that of the Albany waltzer, v(A/b). The results of allelism tests between BUS and Albany waltzer indicated that bus is allelic with v(Alb). From these data, we propose here that the bus mutation could represent another allele of waltzer, now designated v(bus).

Proposal of a new method for narrowing and moving the stimulated region of cochlear implants: animal experiment and numerical analysis.

We have proposed the tripolar electrode stimulation method (TESM) for narrowing the stimulation region and continuously moving the stimulation site for cochlear implants. The TESM stimulates the auditory nerve array using three adjacent electrodes which are selected among the electrodes of an electrode array within the lymphatic fluid. Current is emitted from each of the two lateral electrodes and received by the central electrode. The current received by the central electrode is made equal to the sum of the currents emitted from the lateral electrodes. In this paper, we evaluate whether or not TESM works according to a theory which is based on numerical analysis using an electrical equivalent circuit model of the auditory nerve fibers. In this simulation, the sums of the excited model fibers are compared to the compound action potentials (CAP's) which we obtained through animal experiments. To identify the main parameter while maintaining the amplitude of the CAP (the sum of the fired fibers), we assumed the presence of some parameters from the radial current density profile. In the case of the width value among the parameters being kept constant, the amplitude of the CAP was almost constant; thus, the number of the fired fibers was also almost constant. The width value equals the distance between the points at which the profile of the radial current density of the electrode array and the line of the radial threshold current density of the electrode array intersect. It is possible to determine the measure of the stimulation region or site by controlling the width value and the ratios of the currents emitted from the lateral electrodes. As a result, we succeeded in narrowing the stimulation region by controlling the sum of the currents emitted from the two lateral electrodes. Also we succeeded in continuously moving the stimulation site by modifying the currents emitted from the two lateral electrodes.

Effects of tinnitus on posture: a study of electrical tinnitus suppression.

We investigated the effects of tinnitus on postural responses using posturography. Thirty-three tinnitus patients (19 female and 14 male) ranging in age from 33 to 67 years (mean age, 53) were selected randomly at our outpatient clinic. Nobody complained of dizziness. Posturographic examination was given before and after 30-minute electrical stimulation. Items tested were envelope area, area (root mean square), total length, total length-area, mean amplitude of lateral body sway (mx), and anteroposterior sway (my). Those parameters did not improve in patients without tinnitus relief. Two postural measures (envelope area and mx) showed significant improvement in patients with tinnitus relief. These effects appeared only on positions involving restricted visual feedback. In a comparison of postural measures in patients with and without tinnitus relief, all parameters except total length and mx improved significantly in patients with eyes open. Our study showed that aside from the auditory system, tinnitus can affect balance, implying that tinnitus may be a factor in increasing unsteadiness in patients with tinnitus.

Effects of greater occipital nerve block on tinnitus and dizziness.

We analyzed relationships among tinnitus relief, dizziness, and results of vertical autocorrelation studies of head movement to investigate the effect of greater occipital nerve block on the sensory and motor system in 2 patients with abnormal head movement. Tinnitus improved in 14 (52%) of 28 tinnitus patients after occipital nerve block. The percentage of patients reporting tinnitus improvement (54%, or 7 patients) among 13 patients without a history of trauma was not significantly higher than among 12 patients with trauma (33% or 4 patients). However, tinnitus improvement in patients with dizziness but without trauma was more frequent than that reported by nontraumatic tinnitus patients without dizziness (p<.05). Vertical autocorrelation results while stepping in place were better in patients with tinnitus relief than in those not reporting tinnitus relief (p =.001). Dizziness improved in 8 of 13 patients (62%) with trauma, similar to improvement in 8 of 14 patients without trauma (57%). Improved word perception test results in the presence of noise suggested that improvement in tinnitus and dizziness after occipital nerve block was related to improved attention.

Simple in-office closure of small intractable tympanic membrane perforations after myringoplasty.

Perforations produced following myringoplasty are very difficult to close by ordinary cautery or patching even if they are small. Therefore we decided to close these intractable perforations with a skin graft from the cartilaginous ear canal. Our method is an in-office operation under local anesthesia. After the removal of epithelium from around the perforation a skin graft was placed by the over-lay method. A total of 11 patients were treated, of which 81.8% (9/11) demonstrated successful closure in the initial surgery and two re-perforations were successfully closed by a second and third operation, respectively. The technique used in this surgery is relatively easy and appropriate for in-office operations. The method's advantages include decreased invasiveness with minimal anesthesia and no requirement for ear canal packing or fixatives, and cosmetic benefit. This method also can be applied to perforations caused by chronic otitis media, traumatic perforations, and perforations after inserting tubes.

Preliminary study of improved perception of words with the same sound but different intonation in tinnitus patients following electrical stimulation of the ear.

The present study aimed to explain how tinnitus relief following electrical promontory stimulation affects detection of changes in pitch frequency. To determine the effects of tinnitus relief on the auditory system. Japanese words with the same sound but different intonation were used to verify the effects of tinnitus relief on pitch detection in tinnitus patients Eight out of 11 patients experienced relief of tinnitus following treatment. The averaged number of the ratio in 8 patients with relief of tinnitus, 0.58, was significantly higher (p < 0.02) than that in 3 patients without relief, 0.15. In comparison with averaged hearing level, there was no significant difference in averaged hearing level between 8 patients with relief of tinnitus (52.4 dBSL; SD: 11.4) and 3 without relief of tinnitus (58.0 dBSL; SD: 14.7) (p > 0.68). No significant difference in age between patients with and without relief of tinnitus was observed.

Improved word perception in tinnitus patients following electrical stimulation of the ear: a preliminary report.

The present study showed that there were close relationships between tinnitus relief and improved word perception by means of a grammatically correct but non-sense Japanese word perception test. Fourteen out of 20 patients reported tinnitus relief and improvement in hearing. Nine out of the 14 patients were thought to be significantly improved in word perception. Improved word perception was observed in 7 out of 10 patients whose ears tested were opposite to ears treated while in 2 out of 10 patients whose ears tested were the same as ears treated. Improved word perception was observed in 5 patients at one segment, 2 patients at two segments and 2 patients at three segments. Improved word perception was observed in one patient at the first segment, 5 patients at the second segment, 5 patients at the third segment and 5 patients at the fourth segment. There were no significant differences in hearing level nor age in patients with and without relief of tinnitus.

Improved word perception following electrical stimulation of the ear in hearing-impaired patients without tinnitus.

Improved word perception in hearing-impaired patients following electrical stimulation of ears was shown by means of a grammatically correct but non-sense Japanese 4-segment sentence perception test. Improved word perception was reported in 15 out of 20 patients without tinnitus following electrical stimulation of ears. In 11 out of 15 patients, the number of incorrect words significantly decreased, showing that electrical stimulation of ears improved word perception. Improved word perception was observed in 5 out of 8 patients whose tested ears were contralateral to treated ears while in 8 out of 12 patients whose tested ears were the same as treated ears. The present study suggests that electrical stimulation of ears improves word perception in hearing-impaired patients without tinnitus.

Evaluation of the tripolar electrode stimulation method by numerical analysis and animal experiments for cochlear implants.

We have proposed the Tripolar Electrode Stimulation Method (TESM) which may enable us to narrow the stimulation region and to move continuously the stimulation site for the cochlear implants. We evaluated whether or not TESM works according to a theory based on numerical analysis using the auditory nerve fiber model. In this simulation, the sum of the excited model fibers were compared with the compound actions potentials obtained from animal experiments. As a result, this experiment showed that TESM could narrow a stimulation region by controlling the sum of the currents emitted from the electrodes on both sides, and continuously move a stimulation site by changing the ratio of the currents emitted from the electrodes on both sides.

Proposal of a new auditory nerve stimulation method for cochlear prosthesis.

The stimulation electrodes of cochlear implants are covered by a lymph liquid with high electrical conductivity, which causes the transmitted information to be reduced by channel interaction. Even if this problem were solved, the stimulation regions may be discrete; therefore, there may be regions in which the electrode array cannot stimulate selectively. To solve these problems, we proposed a new auditory nerve stimulation method which we call the tripolar electrode stimulation method for cochlear implants. Our method stimulates using 3 adjacent electrodes selected from among the electrodes of the electrode array. The center electrode receives the currents emitted from the electrodes on both sides. We conducted animal experiments using this method. On the basis of the results we obtained, we concluded that our method may succeed in narrowing the stimulation region and continuously moving the stimulation site.

Surgical results of tympanoplasty with hokudai-shaped partial and total ossicular replacement prostheses.

The surgical results of tympanoplasty using a ceramic partial ossicular replacement prosthesis (PORP) or a ceramic total ossicular replacement prosthesis (TORP) were analyzed. The present study included 25 ears in 22 patients who underwent tympanoplasty between December 1986 and September 1994 and were followed up for more than 6 months postoperatively. Because the ceramic prosthesis was extruded from 2 of the 25 ears, the surgical results in the other 23 ears were analyzed, Surgical results were assessed according to a criterion that permits comparison with data from around the world. The criterion considers a postoperative airbone gap within 20 dB as a success. According to this criterion, the success rate was 90.9% for PORP, 50.0% for TORP, and 69.6% in total. These results are comparable with those found at other centers.

Thyroplasty type I with ceramic shim.

To prevent side effects from a silicone shim in Isshiki thyroplasty type I, we used a ceramic shim in 10 patients with unilateral recurrent laryngeal nerve paralysis. No published reports have described the use of ceramic in this type of surgery. According to the degree of glottic insufficiency, ceramic shims of various heights were inserted into the fenestration made in the thyroid ala. All patients experienced subjective improvement of voice postoperatively. Laryngoscopies in most cases showed that glottic insufficiency improved postoperatively. In the postoperative examination, the maximum phonation time improved an average of 3.7 s, and the mean flow rate improved an average of 331 ml/s. We have analyzed the relationship of these improvements to the degree of glottic insufficiency and have compared our results with those of other investigators.

An experience of the usage of electrical tinnitus suppressor.

An electrical tinnitus suppressor based on the use of an extracochlear stimulator has been developed at Hokkaido University, Sapporo, Japan, and was implanted in 2 male and 2 female patients. Tinnitus improved in all patients because the auditory nerve was able to be stimulated at home whenever patients wanted treatment. Additional benefits reported after electrical stimulation of the cochlea included sound sleep, relaxation in all cases, and improved hearing acuity in Cases 1, 2, and 4. Minimal temporary complications, including habituation and ear drum perforation, were observed.

A portable digital speech-rate converter for hearing impairment.

A real-time hand-sized portable device that slows speech speed without changing the pitch is proposed for hearing impairment. By using this device, people can listen to fast speech at a comfortable speed. A combination of solid-state memory recording and real-time digital signal processing with a single chip processor enables this unique function. A simplified pitchsynchronous, time-scale-modification algorithm is proposed to minimize the complexity of the DSP operation. Unlike the traditional algorithm, this dynamic-processing algorithm reduces distortion even when the expansion rate is only just above 1. Seven out of 10 elderly hearing-impaired listeners showed improvement in a sentence recognition test when using speech-rate conversion with the largest expansion rate, although no improvement was observed in a word recognition test. Some subjects who showed large improvement had limited auditory temporal resolution, but the correlation was not significant. The results suggest that, unlike conventional hearing aids, this device can be used to overcome the deterioration of auditory ability by improving the transfer of information from short-term (echoic) memory into a more stable memory trace in the human auditory system.

Surgical Method for Implanted Tinnitus Suppressor.

A surgical method of fully internal tinnitus suppressor is presented. The surgical approach for the placement of the electrode is very simple and causes less injury to the cochlea. This surgical approach is quite similar to the exploratory tympanotomy. The unit is located at the seat which is drilled in the mastoid bone just behind the external ear canal. The stimulating electrode is introduced to the middle ear beneath the skin of the ear canal on the posterior bony wall. The tip of the electrode located on the promontory is secured by the fascia The primary coil is contained in the Behind-the-Ear case.

Cochlear pathology following chronic electrical stimulation of the auditory nerve: II. Deafened kittens.

The present study examines the effects of long-term electrical stimulation of the auditory nerve on cochlear histopathology and spiral ganglion cell survival in young sensorineural deafened cats. Eight kittens were deafened using kanamycin and ethacrynic acid, and implanted with bipolar or monopolar scala tympani electrodes. Following recovery from surgery the animals were unilaterally stimulated using charge balanced biphasic current pulses for 450-1730 hours over implant periods of up to four months. Charge densities varied from 0.6-0.9 microC.cm-2 geom. per phase for monopolar electrodes to 12-26 microC.cm-2 geom. per phase for the bipolar electrodes. Electrically-evoked auditory brainstem responses (EABRs) were periodically monitored during stimulation to confirm that the stimulus levels were above threshold, and to monitor any change in the response of the auditory nerve. Following completion of the stimulation program cochleae were prepared for histological examination. EABRs exhibited relatively stable thresholds for both stimulated and implanted, unstimulated control cochleae for the stimulus duration. While the growth in response amplitude as a function of stimulus current remained stable for the bipolar control and monopolar stimulated cochleae, the five cochleae chronically stimulated using bipolar electrodes exhibited a moderate to large increase in response amplitude. These increases were associated with a more widespread fibrous tissue response which may have altered the current distribution within these cochleae. Implanted control cochleae exhibited significantly less tissue response within the scala tympani. Importantly, we observed no statistically significant difference in the spiral ganglion cell density associated with chronic electrical stimulation when compared with unstimulated control cochleae. While the present study supports the safe application of cochlear implants in young profoundly deafened children, it does not corroborate previous studies that have reported electrical stimulation providing a trophic effect on degenerating auditory nerve fibres.

[Electroconduction system for implantable tinnitus suppressor].

The purpose of this study was to introduce the electroconduction system for an implantable tinnitus suppressor. This system is a modification of the extracochlear implant system, which was developed at Hokkaido University. This system consists of a stimulator and two coils. One of the coils is implanted inside the temporal bone and its size, including the current limiter, is 9 mm long, 6.4 mm wide and 6 mm thick. Another is contained in the plastic case which is used for hearing aids. The efficacy of conduction depends on the wave frequency. The most effective frequency was about 30 kHz. The maximum current required to relieve tinnitus is 100 microA when using this system. The heat emitted from the coil inside the case is so minimal at an intensity of 100 microA as to be negligible systemically. The electromagnetic coupling system works well for more than 4 months in saline.