Effects of chronic electrical stimulation on spiral ganglion neuron survival and size in deafened kittens.

We have studied spiral ganglion cell (SGC) survival and soma size in neonatally pharmacologically deafened kittens. They were implanted with a four-electrode array in the left cochlea at 100 to 180 or more days of age. Eight animals were chronically stimulated approximately 1000 hours over approximately 60 days with charge-balanced, biphasic current pulses; three were unstimulated controls. Using three-dimensional computer-aided reconstruction of the cochlea, the SGC position and cross-sectional area were stored. SGC position was mapped to the organ of Corti by perpendicular projections, starting from the basal end. The basal region of the cochlea was divided into three 4-mm segments. SGC survival (number per 0.1 mm of the length of the organ of Corti) and soma size for stimulated cochleae were compared statistically with implanted but unstimulated cochleae. There was no evidence of an effect of electrical stimulation on SGC survival under this protocol and with this duration. On the other hand, the cell size on the stimulated side was significantly larger than the control side in the middle segment (4 to 8 mm from the basal end). SGCs undergo a reduction in size after prolonged auditory deprivation; however, these changes may be partially moderated after chronic intracochlear electrical stimulation.

Effects of intracochlear factors on spiral ganglion cells and auditory brain stem response after long-term electrical stimulation in deafened kittens.

Using an animal model, we have studied the response of the auditory brain stem to cochlear implantation and the effect of intracochlear factors on this response. Neonatally, pharmacologically deafened cats (100 to more than 180 days old) were implanted with a 4-electrode array in both cochleas. Then, the left cochlea of each cat was electrically stimulated for total periods of up to 1000 hours. After a terminal (14)C-2-deoxyglucose (2DG) experiment, the fraction of the right inferior colliculus with a significant accumulation of 2DG label was calculated. Using 3-dimensional computer-aided reconstruction, we examined the cochleas of these animals for spiral ganglion cell (SGC) survival and intracochlear factors such as electrode positions, degeneration of the organ of Corti, and the degree of fibrosis of the scala tympani. The distribution of each parameter was calculated along the organ of Corti from the basal end. There was a positive correlation between SGC survival and the level of fibrosis in the scala tympani, and a negative correlation between SGC survival and the degree of organ of Corti degeneration. Finally, there was a negative correlation between the 2DG-labeled inferior colliculus volume fraction and the degree of fibrosis, particularly in the 1-mm region nearest the pair of electrodes, and presumably in the basal turn.

Factors contributing to phoneme recognition ability of users of the 22-channel cochlear implant system.

A study was carried out to determine which factors contributed to the vowel and consonant recognition ability of recipients of the 22-channel cochlear implant system. On the basis of the statistical analysis, no isolated factor showed a strong correlation with vowel recognition score. On the other hand, negative correlations were found between patients' consonant recognition scores and postoperative psychophysical percepts such as threshold levels and maximum comfortable loudness levels. However, multiple regression analysis also showed that the combination of lower threshold levels, a larger number of usable electrodes, and wider dynamic ranges contributed to higher consonant recognition scores.

Dimensions of the scala tympani in the human and cat with reference to cochlear implants.

The width, height, and cross-sectional area of the scala tympani in both the human and cat were measured to provide dimensional information relevant to the design of scala tympani electrode arrays. Both the height and width of the human scala tympani decreased rapidly within the first 1.5 mm from the round window. Thereafter, they exhibit a gradual reduction in their dimension with increasing distance from the round window. The cross-sectional area of the human scala tympani reflects the changes observed in both the height and width. In contrast, the cat scala tympani exhibits a rapid decrease in its dimensions over the first 6 to 8 mm from the round window. However, beyond this point the cat scala tympani also exhibits a more gradual decrease in its dimensions. Finally, the width of the scala tympani, in both human and cat, is consistently greater than the height.

The blood vessels in Reissner's membrane of the rat.

Blood vessels on Reissner's membrane were electron-microscopically found in 24 out of 30 rats of the Wistar strain. The vessels were noted in the upper turns, mainly in the third turn of the cochlea. They originated from radiating arterioles in the upper spiral ligament and took straight courses radially down to the spiral limbus, and further to the modiolus, running along the surface of the scala vestibuli side of the membrane. Their diameter was approximately 4 microns. Bifurcated blood vessels were occasionally detected in 3 out of the 24 rats that possessed the vessels in the membrane. From the morphological point of view the blood vessels in Reissner's membrane may possibly have some function in the inner ear of the rat.

Japanese-language results for the speak strategy from Cochlear Pty Limited.

Recognition of speech sounds with a new speech-coding strategy, Speak, was compared with that of the Multipeak (Mpeak) strategy. Results of consonant, word, and sentence tests on 10 postlingually deaf subjects demonstrated that the performance of the Speak strategy significantly exceeded that of the Mpeak strategy under both quiet and noise conditions. Information transfer ratios for consonant features were improved by 20% to 40% with the Speak strategy under the noise condition. Thus, the Speak coding strategy can provide better speech sound perception than the Mpeak coding strategy.

Advanced necrotizing external otitis treated by suboccipital craniectomy.

Necrotizing external otitis is a destructive infection caused by Pseudomonas aeruginosa. It may spread to surrounding soft tissue, cartilage and bone from the skin of the external canal and cause cranial nerve palsy. Most of the disease occurs in elderly diabetics and is accompanied by high mortality in an extended case in spite of intensive antibiotic therapy. A case of advanced necrotizing external otitis with palsies of VI to XII cranial nerves was presented. The patient, 69-year-old male, took a favorable course after complete debridement by suboccipital craniectomy followed by intensive antibiotic therapy. This procedure was performed by co-operation with a neurosurgeon. Characteristics of the pathology, criteria for the diagnosis and method of treatment are discussed; the authors stress the importance of early diagnosis and necessity of complete meticulous debridement on the extended case with multiple nerve palsies.

Cochlear and fast electrical responses to frequency modulated tones: a frequency specific stimulus.

Some characteristics of "the fast response" to frequency modulation were explored here by examining (1) CM and AP in animal experiment and (2) BER in human study. CM to frequency modulated tone showed frequency change and amplitude change, the latter of which is probably due to frequency characteristics of the sound conductive system of the ear. Compared with AP to tone burst, latency and amplitude of AP to FM tone depends less on stimulus intensity. AP to FM tone is suspected to be a result of new excitement of the restricted area stimulated by shifted frequency. The result of analysis on human BER is well consistent with the result of AP study in animal experiment, and latency curves of BER were to some extent linear to a log scale of shifted frequencies. Thus, FM tone is possibly a frequency specific stimulus.

Speech perception with multi-channel cochlear implant of short duration pulse strategy.

A multi-channel cochlear implant (Nucleus type) was implanted in a 40-year-old female Japanese patient who became totally deaf after meningitis. The formant-based speech processing strategy was used, but a narrow pulse width of 22-42 microseconds was required because of intermittent difficulty in controlling the pulse amplitude. The patient was tested with a speech tracking test and could recognize 24 bunsetsues (the minimum meaningful unit of the Japanese sentence) per minute using the cochlear implant plus lipreading and 14.3 bunsetsues for the lipreading alone after 3.5 months' training. The patient was also able to understand usual conversational sentences spoken a little slowly. Scores of vowel and consonant tests reached 70% and 54% respectively for the cochlear implant alone, and 100% and 73% for the cochlear implant plus lipreading. This study has also shown that cochlear stimulation with very narrow pulse widths can be used, and restore speech comprehension ability for the Japanese.

The inferior collicular potential in acoustic and electrical stimulation of the cochlea: an experimental study of guinea pig.

We made experiments of the inferior collicular potentials in acoustic and electrical stimulation for the purpose of studying fundamental issues for cochlear implantation. Guinea pigs with normal Preyer's reflex were used for this study. The results were as follows: (1) in acoustic stimulation relatively wide and large waveforms were gained but in electrical stimulation sharp and narrow ones were gained, (2) in acoustic stimulation the input-output curve of latency and amplitude was biphasic but in electrical stimulation it was monophasic. For this reason, in acoustic stimulation by click, when the intensity is low (under 80 dB SPL) stimulus site would be comparatively low frequency fibers. When the intensity is high (over 80 dB SPL) the stimulus site would shift to high frequency fibers. Therefore, many more neighboring fibers start responding. This results in biphasic input-output curves of latecy and amplitude. By electrical stimulation, however, it would be possible to stimulate only a restricted area among the bipolar electrode. Therefore, as the intensity increases, the response amplitude increases and becomes saturated at a constant level. This results in monophasic input-output curves of latency and amplitude.

[Estimation of surviving auditory nerve by electrically evoked auditory brainstem response (FABR)--comparison between extra-cochlear stimulation and intra-cochlear stimulation].

This study investigated the possibility of using electrically evoked auditory brainstem response (EABR) for predicting surviving spiral ganglion cell populations. EABR recordings were made from six kanamycin induced deaf cats by the round window monopolar stimulation (RW) and the scala tympani bipolar stimulation (ST). On completing the electrical stimulation, each animal was sacrificed and prepared for histological examination. The spiral ganglion cell populations were estimated by classifying them into four groups (0-25%, 25-50%, 50-75%, 75-100%) as a percentage of survival cells under magnification. EABR thresholds and input-output function of amplitude were compared with microscopic findings of surviving spiral ganglion cell populations. The results were as follows: 1) The rate of amplitude growth in response to increased stimulus intensity of electrically evoked potentials from ST was gradual, but that of RW was steep. 2) The vestibular potentials were elicited by RW, and at a lower stimulus intensity the RW waveform began to become distorted by the myogenic potentials. 3) EABR threshold was a poor predictor of surviving spiral ganglion cell populations. 4) There was a correlation between surviving spiral ganglion cell populations and the slope of the input-output functions of ST EABR. However, there was no correlation between that of RW EABR and the slope.

[Effects of chronic electrical stimulation on cochlear nuclear neuron size in deaf kittens].

It is now well recognized that normal afferent innervation is necessary for development of the auditory pathway. This study investigated the effect of chronic electrical stimulation of the auditory nerve on the size of cochlear nucleus somata of neonatally deafened kittens. Four kittens were deafened by using kanamycin and ethacrynic acid at 10 days of age and implanted at various ages with an active intracochlear implant in the left side and a dummy implant in the right side, and chronically electrically stimulated from ages 98-142 days for approximately 1000 hours at twice the EABR threshold. After chronic stimulation or after an equivalent period in the controls, the animals were injected with 2-deoxyglucose (2DG) and stimulated electrically for 45 minutes, then processed for autoradiography. Then the sections were stained for Nissle substance, and the cross-sectional areas (CSSA) of approximately 33,000 neuron somata in the cochlear nuclei were measured with an image-analysis system. Soma sizes in regions with 2DG uptake were compared with those without the uptake. The CSSA of 2DG-labeled regions was usually significantly larger than that of the unlabeled regions, but there were no significant right-left differences. Thus, chronic electrical stimulation of a restricted sector of the cochlea is correlated with a larger soma size in the corresponding region of the cochlear nucleus.

[Changes of the threshold level in patients with 22-channel cochlear implant].

Psychophysical responses of the patients to electrical stimulation were examined in order to clarify long-term effects of the cochlear implant in 9 patients who had received a 22-channel cochlear implant. Measured items were the minimal threshold level (T-level), the maximum comfortable level (C-level), and the dynamic range between T- and C-level. Measurements were repeated for each electrode every three months over more than 6 months. Following results were obtained. 1) The changes of the T-level were classified into four types as follows, a type with no change, a type with gradual decrease, a type with decrease in two to three months followed by gradual increasing threshold and a type with gradual increasing just after surgery. Even in a last type, the maximum increase in the T-level did not exceed 200 microA and, in most cases, these changes were stabilized within a few months after implantation. 2) The dynamic range gradually increased. It was obvious in both in the middle and apical electrodes, while such increased threshold was not observed in the basal electrodes. 3) In some cases, a few basal electrodes could not been used since they caused uncomfortable sensation or those dynamic ranges became below a certain extent. As a result, it was suggested that the electrical stimulation had not induced serious degeneration of the ganglion cells and the auditory nerve fibers. The reduction in the number of usable electrodes might be due to the surgical trauma to the intracochlear tissue. Therefore, exposing of the scala tympani should be minimal in order to avoid the damage of the cochlea.

[Comparison of speech perception with cochlear implant and hearing aid--analysis according to speech strategy and hearing level].

This study was carried out to compare the speech perception ability of patients using hearing aids with hearing levels of 81dB or more (55 patients) and those with cochlear implants (67 patients). The patients with hearing aids were divided into group A (hearing levels 81-90dB, 7 patients), group B (91-100dB, 11 patients), group C (101-110dB, 19 patients), group D (111-120dB, 7 patients), and group E (121-130dB, 6 patients). The patients with cochlear implants were using the strategies of F0F1F2 (14 patients), MPEAK (32 patients) and SPEAK (21 patients). Speech perception tests of monosyllables, words, and sentences under conditions of auditory plus vision were administered. The means and standard deviations of percentages giving the correct answer in F0F1F2, MPEAK and SPEAK were 45.2 +/- 14.7%, 45.7 +/- 14.6% and 62.6 +/- 15.9% for monosyllables, 44.8 +/- 18.9%, 56.3 +/- 15.0% and 73.4 +/- 15.5% for words, and 64.0 +/- 26.4%, 60.5 +/- 15.9% and 84.7 +/- 13.8% for sentences. In comparison with the results for patients with hearing aids, and speech perception for F0F1F2 and MPEAK was equivalent to that of group C, and that for SPEAK was better than that of group B but poorer than that of group A. In other words, the speech perception ability in conventional cochlear implant strategies--F0F1F2 and MPEAK--corresponded to that of patients with hearing levels of 101-110dB, but that in the new strategy, SPEAK, gave better results than 91-100dB.

[Image analysis of the inner ear with CT and MR imaging: pre-operative assessment for cochlear implant surgery].

Recent progress in magnetic resonance imaging (MRI) has made it possible to obtain detailed images of the inner ear by delineating the lymphatic fluid within the labyrinth. We analyzed CT scans and MR images in 70 ears manifesting profound deafness owing to inner ear lesions and compared their detective ability for inner ear lesions. The following results were obtained. 1) CT scan examination showed slight to extensive ossification of the labyrinth in six ears (9%), whereas MRI examination revealed low to absent signal intensity of the inner ear in nine ears (13%). Therefore, it was concluded that MRI is more sensitive in detecting abnormalities of the inner ear than CT scan. 2) MRI provided useful information as to whether the cochlear turn is filled with lymphatic fluid or obstructed. This point was one of the greatest advantages of MRI over CT scan. 3) Abnormal findings in either or both the CT scan and the MRI were detected in suppurative labyrinthitis occurring secondary to chronic otitis media, bacterial meningitis and in inner ear trauma. However, such abnormal findings were not detected in patients with idiopathic progressive sensorineural hearing loss, ototoxicity or sudden deafness. These findings should be taken into consideration in pre-operative assessment of cochlear implant candidates.

[Clarion 16 cochlear implant (System introduction and use experience in Japan].

The Clarion cochlear implant was developed in the USA and received FDA approval in August 1996. It consists of an implantable cochlear stimulator (ICS), speech processor with headpiece, and in addition, a clinician's programming system and portable cochlear implant tester. One of the features of the device is its stimulation-coding process for which two methods of continuous interleaved sampling (CIS) and compressed analogue (CA) are applicable. Regardless of which is used, stimulation can be provided over 8 channels. The device was used in 2 cases. Both patients were operated on in October 1996, and 16 electrodes in 8 pairs were mounted in the cochlea. Mapping, performed 3 weeks after the operation, showed good speech perception in both patients with only a cochlear implant in the "open-set" status. CIS was used as the stimulation-coding method. CA has yet to be applied.

[Testing of synthetic vowels in patients with 22 channel cochlear implant].

In the 22 multi-channel cochlear implant system, F0 information determines the frequency of electrical stimulation, and F1 and F2 information determine the number of stimulating electrodes. We performed tests using synthetic vowels on 16 patients who had undergone 22 channel cochlear implant surgery and 6 months' speech rehabilitation. Information transmission rates were calculated to analyze the response pattern. As a result, 1) the vowel recognition ability of patients with cochlear implant surgery correlated with the number of electrodes being used. 2) The value of vowel confusion decreased so as to be separated by a pair of stimulating electrodes, and the confusion in F1 information was regarded to be less than that for F2 information.

[Two cases of sensory neural hearing loss as a manifestation of HIV infection].

In patients with HIV infection, oral and pharyngeal pathology frequently occurs, but there have been no reports on cases of deafness in Japan. Herein, the authors report two cases of sensory neural hearing loss in hemophilia A patients infected with HIV through factor VIII concentrates. Case 1 was a 16-year-old male with hemophilia A. He had been administered factor VIII concentrates starting at 6 months after birth. At 8 years of age, HIV antibodies were positive. He was diagnosed as having AIDS after suffering from pneumocystis carinii. He complained of right otalgia and slight vertigo during treatment for a relapse of the pneumocystis carinii. He underwent otological examinations at our department. The right tympanic membrane showed opacification and serous otorrhea was noted. Acute otitis media was diagnosed and tympanotomy was conducted. Afterwards, the right tympanic membrane developed a large perforation and sensory neural hearing loss occurred. Case 2 was a 49-year-old male with hemophilia A. He had been administered factor VIII concentrates from the age of 23 years. At 48 years of age, HIV antibodies were positive. The patient complained of sudden deafness in the right ear and slight vertigo. He underwent otological examinations at our department. The tympanic membrane was normal bilaterally, but sensory neural hearing loss was found in the right ear. It was presumed that acute otitis media directly involving the inner ear had caused a perceptive disorder in case 1 while a pattern of sudden onset of deafness was apparent in case 2.

[Direct observation of the tympanic cavity by the superfine fiberscope].

As a clinical test, direct observation of the middle ear should be ideally performed without any surgical intervention such as myringotomy. This paper reports a newly invented superfine fiberscope which makes it possible to insert through the eustachian tube, and direct views of the middle ear structures on normal subjects and patients. The patients were of a small cholesteatoma and traumatic dislocation of the ossicular chain. All of them were tested with local anesthesia in outpatient clinic. This superfine fiberscope was of great value in observing of middle ear structures as a diagnostic instruments, as that no surgical intervention was necessary in the procedure.

[Clinical study of photodynamic therapy for laryngeal cancer].

Photodynamic therapy (PDT) is an innovative treatment involving the use of a photosensitizer and low powered laser to selectively destroy tumor cells. In the head and neck, its application to laryngeal papilloma, metastatic tumor and oral cancer have been reported but our report on PDT for laryngeal cancer is the only clinical report in Japan. At present, we treat laryngeal cancer by PDT using argon and excimer dye lasers such as the HpD. In the present study, we assessed the utility and safety of PDT and investigated long-term prognosis after this therapy. The subjects were 12 patients with laryngeal cancer who underwent PDT between February 1988 and October 1993. Among them, ten with cancer of the vocal cords underwent PDT as the primary treatment and two underwent PDT because of recurrence after radiotherapy. Under local anesthesia, PDT was performed using a video endoscope (Pentax EB2000). The optimal dose from an argon dye laser was set at 200-500 mW/cm2 of continuous waves for 20 minutes and that from the excimer dye laser was set at 200 J/cm2 of pulse waves (3-4 mJ/pulse, 30-40 Hz). The argon dye laser used was the Fujinon PDT developed by Fuji Photo Optical Co., Ltd. The excimer dye laser used was a product of Hamamatsu Photonics Co., Ltd. 1) Effect of PDT The effect of PDT as a primary treatment for ten patients was classified as CR in eight and PR in two cases, the CR rate being 80.0%. When evaluated only for T1 patients, the results were classified as CR in eight and PR in one. The patient whose response was classified as PR had refused repeated PDT. CR was maintained for five and 13 months in the two patients who underwent PDT as a secondary treatment after radiotherapy. CR was obtained in 83.3% of all patients studied. 2) Duration of the effect of PDT and long-term prognosis The patients were followed up for 14 to 71 months. The longest duration of CR achieved by PDT monotherapy was 65 months. Among the patients who underwent PDT as a primary treatment, one developed local recurrence and underwent radiotherapy. However, the prognosis was uneventful in all other patients. CR after PDT monotherapy was maintained for 42 months in one T3 patient. Two patients with a history of previous treatment thereafter relapsed and underwent total laryngectomy. The larynx could be conserved in 83.3% of all patients. However, it could be conserved in 100% of patients who underwent PDT as a primary treatment.(ABSTRACT TRUNCATED AT 400 WORDS)