Jun-Ichi Suzuki

Evidence for a primary cortical origin of a middle latency auditory evoked potential in cats

The origin of the scalp-recorded auditory evoked potential, Pa, was examined in cats anesthetized with chloralose-urethane and immobilized with gallamine triethiodide. This potential is a prominent positive wave which peaks approximately 12--15 msec following click stimuli. Mapping revealed that Pa is distributed on the scalp in the region overlying cortical area AI, contralateral to the stimulated ear. The cortical potential recorded from AI was a surface-positive wave, restricted to the anterior portion of AI. Laminar analysis of the cortical evoked potentials demonstrated the existence of a dipole generator at that area. The onset of this potential coincided with the onset of the scalp-recorded Pa. Comparison of the scalp and the cortex-recorded potentials showed that both the amplitude-intensity function and the amplitude-rate function for the scalp-recorded potential closely paralleled those recorded from AI. Acute and chronic lesion studies showed that extirpation of AI (particularly the anterior part) almost completely abolished the Pa response. This evidence indicates that the scalp-recorded Pa of cats is generated almost entirely from the anterior part of the contralateral AI.

Role of the otolith organs in generation of horizontal nystagmus: effects of selective labyrinthine lesions

Selective labyrinthine lesions were made to study the origin of excitation in the labyrinth during off-vertical axis rotation. Plugging the semicircular canals abolishes the response to rotation about a vertical axis, but optokinetic after-nystagmus (OKAN) and the sustained horizontal nystagmus induced by off-vertical axis rotation (OVAR) are maintained. After cutting the nerves of the lateral semicircular canals, neither horizontal OKAN nor the continuous horizontal nystagmus associated with off-axis rotation can be induced, although vertical OKN, OKAN and vestibular nystagmus are intact. This supports the theory that labyrinthine activity responsible for the nystagmus induced by OVAR arises in the otolith organs and couples to the oculomotor system through the velocity storage mechanism.

Effects of Rise Time on Simultaneously Recorded Auditory-Evoked Potentials from the Early, Middle and Late Ranges

The view that the effects of stimulus rise time are qualitatively different for early brain stem components, middle latency components and late vertex components of the auditory-evoked responses was reexamined. The amplitudes and latencies of the brain stem response (Jewetts wave V), middle latency components Na and Pa, and vertex potentials P1, N1 and P2, evoked by tone burts of various rise times, were analyzed. Increases in rise time were associated with smaller peak amplitudes and longer peak latencies for all of the components measured. These effects were comparable in magnitude for all the components. The results are interpreted in terms of a delayed and less synchronized neural discharge from the cochlea as rise time is extended.

Brain stem response audiometry at speech frequencies.

Auditory-evoked brain stem response (BSR; wave V) was studied, using tone pips at three speech frequencies (500, 1 000 and 2 000 Hz) as stimuli. The tone pips consisted of 5-ms rise-decay times without a plateau. BSR recordings were made in 10 normal subjects and in 16 subjects with impaired hearing. In the normal subjects, BSR thresholds ranged from 10 to 20 dB SL at these three frequencies. In the subjects with impaired hearing, BSR thresholds corresponded well to conventional pure-tone thresholds at each frequency in cases of low- as well as high-frequency hearing loss. In all subjects with impaired hearing, the BSR thresholds were higher by as much as 25 dB than the pure-tone thresholds. The mean differences between these two thresholds at 500, 1 000 and 2 000 Hz were 11.3 +/- 8.0, 10.9 +/- 6.2 and 10.9 +/- 7.3 dB, respectively. Thus, we conclude that the BSR is useful for objective assessment of hearing thresholds at each of these speech frequencies.

Clinical Evaluation of the Auditory Evoked Brain Stem Response

A clinical evaluation of the auditory evoked brain stem response (BSR) has been performed in eleven artificial, and twelve pathological cases of conductive hearing loss, and also in seven patients with deafness from Menieres disease. The latency of wave V of the BSR was plotted as a function of auditory stimulus intensity (of clicks from 10 dB to 85 dBHL) to produce latency-intensity (L-I) curves for subjects with hearing losses, and compared to those from a normal population. L-I curves from conductive hearing losses of both artificial, and pathological cases showed characteristic horizontal shifts to the right (in dBHL); thresholds determined by BSR audiometry were within 15 dB of the thresholds obtained by standard audiometry (4 kHz) in 83 f of these cases. L-I curves from Menieres patients were within the normal range at high stimulus intensities but showed a marked deviation from normal at low intensities; thresholds estimated by BSR audiometry in Menieres disease were usually lower than those determined by standard audiometry (4 kHz). The results indicate that BSR audiometry can be useful in the evaluation, differentiation, and threshold determination of peripheral auditory pathologies.

Risk factors for recurrent and residual cholesteatoma in children determined by second stage operation

OBJECTIVE To clarify the risk factors for the development of recurrent and residual cholesteatoma in children. METHODS We studied 84 ears of 83 children aged 10 years or younger who underwent a second stage operation 1 year after primary surgery with a canal wall reconstruction procedure, and analyzed the clinical risk factors for recurrent and residual cholesteatoma. RESULTS Recurrent cholesteatoma was detected in 21 ears (25%) and residual cholesteatoma was noted in 35 (42%) of 84 ears. With respect to recurrent cholesteatoma, significant risk factors were determined to be male gender, pars flaccida type of cholesteatoma and the association of otitis media with effusion either in the side affected by cholesteatoma or on the opposite side. On the other hand, congenital type of cholesteatoma was a significant negative risk factor. With respect to residual cholesteatoma, the only risk factor was a posterosuperior type of cholesteatoma. Residual cholesteatoma was sometimes found even when the surgeon had declared complete removal of the cholesteatoma matrix at the time of primary surgery. CONCLUSIONS High incidence of recurrent and residual cholesteatoma was noted at the second stage operation. Occurrence of recurrent cholesteatoma is closely related to eustachian tube dysfunction. Thin and highly proliferative cholesteatoma matrix in children may be responsible for high occurrence of residual cholesteatoma. Therefore, planned staged surgery is preferable to single stage surgery for the treatment of pediatric cholesteatoma.

Development of an Implantable Hearing aid Using a Piezoelectric Vibrator of Bimorph Design: State of the Art

A new, implantable hearing aid has been developed. An ultraminiature electret microphone placed under the skin of the external ear canal transduces sound waves into electrical impulses that are amplified with battery power. The amplified electrical impulses are fed into a piezoelectric vibrator directly in contact with the stapes. The vibrator transduces the electrical impulses into mechanical vibration with minimal consumption of electrical energy. Direct coupling of the vibrator to the stapes allows a high degree of fidelity in the perception of sound. The developmental process and the structure and function of each component are described together with clinical problems. Preliminary and tentative implantation of this new device during middle ear surgery indicated that it would be beneficial to patients who have suffered hearing loss from middle ear disease and whose condition does not lend itself to surgical correction.

Mastoid pneumatization in children with congenital cholesteatoma: An aspect of the formation of open‐type and closed‐type cholesteatoma

Objectives: To clarify mastoid pneumatization in children with congenital cholesteatoma and compare their clinical characteristics. Study Design: The mastoid pneumatization of 34 children with congenital middle ear cholesteatoma, of 34 age‐matched children with unilateral acquired cholesteatoma, and of 17 age‐matched control children without middle ear diseases was studied. Methods: The sizes of the mastoid cells were measured from 1.5‐mm sliced semiaxial sections of a temporal bone computed tomography scan. The sum of the two areas from the two images, one showing the lateral semicircular canal and the other, 3 mm below this, was defined as the area of the pneumatized mastoid cells. Results: The mastoid cells in ears of children with congenital cholesteatoma were poorly pneumatized compared with those of control children without middle ear diseases, but were better pneumatized compared with those of children with acquired cholesteatoma. In children with congenital cholesteatoma, the degree of pneumatization in the cholesteatoma side was significantly poorer than that in the opposite side. A well‐pneumatized mastoid was seen in ears with no episode of otitis media, in ears with the open‐type cholesteatoma, and in ears with ossicular anomalies. Conclusions: The presence of cholesteatoma matrix accelerates the inflammatory response when middle ear infections occur, and this probably leads to the suppression of mastoid pneumatization. The authors also propose the hypothesis that cholesteatoma in most congenital cases is the open type, and that middle ear inflammation may contribute to the formation of cystic and closed‐type cholesteatoma.

Binaural Interaction of a Beating Frequency-Following Response

Frequency-following responses to 500-Hz tone bursts presented to the left ear and 540-Hz tone bursts presented to the right ear were recorded from human subjects. Recordings were made both under monaural and binaural conditions. The responses summed over monaural conditions (for left and right ear stimulation) were larger than the responses obtained in the binaural condition. This binaural interaction shows that the frequency-following response reflects binaural processing probably occurring at or below the level of the inferior colliculi.

Cochlear ototoxicity of chlorhexidine gluconate in cats

SummaryChlorhexidine gluconate is a derivative of chlorhexidine and is a popular desinfectant with a strong bactericidal action that is widely used for preoperative sterilization in ear surgery. The purpose of this investigation is to ascertain the potential ototoxity of this agent. After topically applying chlorhexidine gluconate solutions to the middle ear cavities of 12 cats, we observed the excised cochleas using both scanning and transmission electron microscope studies. Either 0.05% or 2% chlorhexidine gluconate solutions were infused into the right ear of the test animal through one of two tubes chronically installed in the tympanic bullae. The left ears were utilized as controls and were infused with sterilized physiological saline. The solutions were administered once every other day for three separate infusions. Nine animals were decapitated 7 days after the third application, while the other three animals were sacrificed at 4 weeks. In the 2% chlorhexidine group, we found that hair cells in the organ of Corti had degenerated and had lost their hair bundles over a wide range. This pathology was more marked in the lower cochlear turns. In the animals sacrificed at 4 weeks, the injuries present seemed to have progressed. Even at a clinical concentration of 0.05%, chlorhexidine caused intracellular degeneration but with little surface damage. Our findings would suggest a cause of hearing loss when chlorhexidine is used clinically in the ear.