Minoru Takeyama

The Effect of Crossed Olivo-cochlear Bundle Stimulation on Acoustic Trauma

To investigate whether the crossed olivo-cochlear bundle (COCB) functions in a protective manner, albino guinea pigs were exposed to sounds of varying intensity (110-130 dB SPL, 3-30 min) with or without electric stimulation of COCB, and the threshold shifts of the compound action potential (CAP) were examined. A statistically significant protective effect was observed in animals exposed to stimuli of intermediate intensity which induce threshold shifts of 50 to 55 dB on average. No protective effect was observed in the groups exposed to greater or milder stimuli. These results are discussed in the light of the available literature.

The Hearing of the Patients Treated with Hemodialysis: A Long Term Follow-Up Study

Sensorineural hearing loss is frequently found in the patients under the treatment with hemodialysis, but the responsible etiological factor(s) still remains controversial. The purpose of the present study was to determine by a long term follow-up study whether hemodialysis per se or other factors induce sensorineural hearing loss. Thirty-seven patients with the observation periods of 4 years or longer were selected for the analysis. Hearing tests were performed soon after the initiation of hemodialysis and every 3 to 12 months thereafter. Significant hearing loss was found in 16 cases (31 ears) at the first test. Although 3 cases (5 ears) of the initially normal group and one case (2 ears) of the group with already existing hearing loss exhibited significant hearing loss, the change in the hearing level was quite minimal in remaining 67 ears during the observation period. Although the cochlea in patients under the treatment with hemodialysis is susceptible to various insults, we conclude that hemodialysis per se does no harm to the cochlea and the hearing can be maintained at the pre-hemodialysis level in the majority of the cases.

Pathophysiology and Prognosis of Sudden Deafness with Special Reference to the N1 Latency

Electrocochleography (ECochG) was performed in 84 patients with sudden deafness which were classified into 3 groups according to the ECochG findings, i.e. the unchanged N1 latency, the prolonged N1 latency and the absence of N1 response. The cause of hearing loss in the first group was thought to be strial, postsynaptic or mild cochlear damage and that in the second to be vascular, sensory or neural damage. The first group showed a better prognosis than those of the other two.

The Effect of Furosemide on the Endocochlear Potential in Ears with Experimentally Induced Endolymphatic Hydrops

The endocochlear potential (EP) was measured in 38 guinea pigs with experimentally induced endolymphatic hydrops at the 3rd, 6th, 12th and 24th postoperative weeks, and the effects of furosemide (FUR, 50 or 80 mg/kg) on the EP were examined. A time-related reduction of the EP from the normal value and increased susceptibility to FUR were disclosed in the hydropic animals. Furthermore, 24-week animals given 80 mg/kg FUR showed a significantly slower recovery rate of the EP than the other groups, indicating impairment of the strial function progressive with post-operative time. The negative component of the EP was considered to be unimpaired until at least 12 weeks after the surgery.

Electrophysiological Aspects of Surgically-Induced Endolymphatic Hydrops

Endolymphatic hydrops, a characteristic finding in Meniere’s disease can be induced in guinea pigs by surgical obliteration of the endolymphatic duct and sac. Since the reports by Harada [1], Naito [2], and Kimura [3], this hydropic animal has frequently been used as an animal model of Meniere’s disease. The purpose of the present paper is to summarize the results of our 10-year study on these animals [4–9] and to review the recently published articles by other investigators. In the present study, endolymphatic hydrops was induced in 136 albino guinea pigs by obliterating the endolymphatic duct and sac. The presence of the hydrops was histologically confirmed in a majority of the cases (Fig. 5.1). The endolymphatic potential (EP) was recorded through the round window and the recording electrode for other cochlear potentials was placed at the round window. The sound stimuli were clicks generated by a 90 μs rectangular pulse and tone bursts of 0.5–16 kHz with a 1 ms rise-fall time and a 10 ms duration. Similar methods were used in the majority of the reports reviewed in the present paper. Therefore, the methods or the conditions of the experiments used elsewhere will be described only when they differ from ours.

Studies with electrocochleography and auditory brainstem response in Ramsay Hunt syndrome.

Eighteen cases of Ramsay Hunt syndrome were examined with electrocochleography and auditory brainstem response. Hearing was normal in 4 cases, while the other 14 exhibited sensorineural hearing loss ranging from mild to moderate in severity. Although the I-V interwave latency in all cases was within or slightly outside of the normal limits, the N1 latency was significantly prolonged in 8 cases proportionately to the degree of hearing loss at 4 and 8 kHz. The histopathological findings reported so far have indicated that the main lesion in this syndrome is in the internal auditory canal (2, 3, 4, 5). The results obtained in the present study, however, clearly show that the main site responsible for the hearing loss is not in the retrocochlear region, but in the cochlea. The possible mechanism of the cochlear involvement in this syndrome was discussed.

Evaluation of eustachian tubal functions in patients with otitis media with effusion

Eustachian tubal function in patients with otitis media with effusion (OME) was qualitatively evaluated. Following observation of middle ear pressure, draining function of the Eustachian tube was tested by introduction of specially prepared dye into the middle ear and subsequent inspection of the nasopharyngeal opening of the tube for dye during application of swallowing. Obtained were followings:1. In cases of children, Eustachian tube may be reversibly functioned by equalizing the negative middle ear pressure to the ambient pressure. Draining function was considerably improved in 82.9% of cases. On the contrary, equalization of pressure difference may not provide the improvement of the Eustachian tubal function in cases of adults. Improvement in draining function was achieved only in two cases out of 34. These suggest that tubal dys-function is usually constituted by temporary functional disturbance of tubal opening and closing mechanism caused by persistent middle ear negative pressure in children, whereas Eustachian tube muscles are mainly involved in adults.2. Application of swallowing induced two different types of pressure change in the middle ear;(1) the positive pressure change followed by negative change (observed in 25% of cases), (2) just the negative pressure change (75%). Negative pressure dominant change may be considered to mainly contribute to the development of OME