Feasibility of the implantable microphone for the totally implantable hearing aid was investigated in 4 patients with middle ear cholesteatoma at the second stage of the staged intact canal wall tympanoplasty. Electret condenser microphone coated with acrylic resin was inserted in the tympanic cavity, and the test sound was fed through an earphone into the external ear canal. Sound pressure registered in the tympanic cavity was lower by 20-30dB than that in the ear canal below 5.5kHz; at higher frequencies, it decreased further. Although implantation of microphone in the tympanic cavity has problems such as, 1) possible change in functional features after implantation, 2) lower in sensitivity compared to implantation under the canal skin, and 3) interference by intrinsic noise in the tympanic cavity, it also has advantages in preventing extrusion and in avoiding accidental loud noise induced by touching around the ear canal.
The screening audiometrical study was performed on 1346 employees of a brewery factory. The test result revealed that there was an increased threshold at 1000Hz or/and 4000Hz in 325 out of 1346 employees (24.1%). After screening audiometry, these 325 cases received conventional audiometry. Audiograms from these cases mostly showed a gradually high tone loss or c5 dip type as frequently observed in industrial deafness. As an intense noise level was observed in several plants out of 12 consisting of this brewery factory, it was concluded that the hearing loss in these 325 cases seemed to be due to industrial noise in this brewery factory. Most cases with hearing loss were the employees who have worked over 30 years under noisy condition.
For the purpose of evaluating hearing level of handicapped children, we have carried out comparative studies of evoked response audiometry (ERA), conditioned orientation reflex audiometry (COR) and behavioral observation audiometry (BOA). Fifty-five handicapped children (mainly cerebral palsy and mental-motor retardation) at Hokkaido Prefectural Rehabilitation Center For Handicapped Children, Sapporo Unit varying from 4 months to 6 years and 4 months of age were selected for this study. Subjects were classified by 3 groups (group 1-success in COR, group 2-results of COR equivalent to BOA response, group 3-failure in COR). The children of group 1 were significantly elder compared with those of group 2 and 3, but there was no difference between diseases. In group 1, COR threshold was almost 10±20 (±1 SD) dB higher than ERA threshold, but significantly correlated together. In group 2, COR threshold was almost 35±20dB higher than ERA threshold, however, significant correlation was maintained. ERA threshold was correlated with BOA threshold rather than COR threshold. In group 3, BOA threshold was much higher than ERA threshold and there were no correlation between both thresholds. Even in handicapped children, BOA and COR were useful as evaluating their hearing threshold and usually, its threshold correlated with ERA threshold.
For glycerol test, 500ml of 10% glycerol solution was given intravenously to prevent glycerol-induced hemolysis and the other side effects. However, to shorten the test procedure and to avoid the side effects we administered only 200ml of glycerol intravenously to 17 ears with Meniere's disease, 4 ears with syphilitic labyrinthitis, one with contralateral delayed endolymphatic hydrops. Pure tone audiometry and sampling of blood were performed before and 30, and 60 minutes after intravenously administration of glycerol. From the blood samples, the concentration of glycerol and serum osmolality were investigated. We performed both 200ml and 500ml glycerol tests separately in 17 ears with endolymphatic hydrops. Only 2 ears out of 17 ears showed different test results. There were also no statistical differences between the 200ml and 500ml methods in terms of improvement in pure tone threshold between 125Hz and 8000Hz. There were some differences in the blood concentration of glycerol and in serum osmolality when 200ml or 500ml of glycerol was used intravenously or 50g orally. Only two of 22 patients who were given 200ml of glycerol showed side effects as nausea and headache. Of 22 ears with endolymphatic hydrops who underwent 200ml glycerol test, 11 ears (50%) were regarded as positive. Klockhoff and Lindblom's original method and the other reported methods require more than 3 hours for glycerol test. This long test duration made some patients tired. Oral administration also gave them much more side effects than our 200ml method.
The sensitivity of the following 3 methods for detecting amplitude-modulation following response (AMFR) was evaluated: (1) visual analysis of waveform cofiguration, (2) phase spectral analysis and (3) spectral amplitude analysis (response determination by S/N ratio calculated from spectral amplitudes). AMFR was examined in 10 adults with normal hearing while wake and during sleep, and in 10 young children with normal hearing during sleep. The stimulus was a 1000Hz, 50dBnHL sinusoidally amplitude-modulated tone with a modulation depth of 95%. The modulation frequency was varied from 20 to 200Hz in 20Hz steps. Response was determined by each of the 3 methods and the results were compared. Phase spectral and spectral amplitude analyses were far more sensitive than visual analysis. The results of phase spectral analysis were correlated to those of spectral amplitude analysis, but the detectability of phase spectral analysis was slightly better than spectral amplitude analysis. These results suggest that the combined application of phase spectral and spectral amplitude analyses was proved as useful for detecting response in AMFR with greater sensitivity.
A new model of extracochlear prosthesis has been developed for the profoundly deaf whose auditory nerves are still alive. Simple tests carried out using our extracochlear stimulator in order to investigate what kinds of sensation were elicited by the electrical stimulation. Pt-Ir electrode was attached to the promontory and a return electrode was placed on the earlobe. First, the current threshold was obtained and then two time-sequential patterns were displayed successively to get the time resolution of the auditory nerves. For this test, twenty patients who were profoundly or slightly deaf were subjected. From these simple tests, it was ascertained that the thresholds and the sensations varied according to the subject. Sensations produced by the stimulation were categorized into two groups. One of them was the sensation like a sound, the other was like a vibration, pain or prickly sensation. Not only auditory nerves but also facial and glossopharyngeal nerves were probably stimulated in this tests. As concerns discrimination between two time-sequential patterns consisting of double pulse series, three patients could clearly distinguish them when the time difference of the double pulse was slightly changed. Signal processing method which transmits both the pitch and the second formant frequency using time-sequential pattern is one of approaches for the extracochlear prosthesis.
Measurement of the distortion product otoacoustic emissions (DPOAE) was carried out in the guinea pig. Frequency ratio of the iso-intensity (60dB SPL) primaries was fixed to 1.2, and f2 was swept from 16kHz to 0.5kHz. Distortion product (DP) audiogram was obtained as a DP level plot against f2 frequency. Normal guinea pigs with intact tympanic bulla showed a normal DP audiogram trace above 2kHz. Perforation of the bulla significantly elevated DPOAE level around 1kHz and depressed it around 4kHz. The initial DP audiogram could be retrieved by plugging the hole. This change was interpreted as an effect of large downward shift of the middle ear resonant frequency which was measured by the middle ear analyser (MEA). The effect of the middle ear dynamics upon the DPOAE measure can not be over-estimated especially in the small experimental animals, because their small middle ear cavities have large contribution to determine the overall middle ear transfer functions.
The usefulness of canal simulator for determining suitable characteristics (frequency response and maximum output level) of custom in-the-canal hearing aids (ITCs) was studied in 37 patients (40 ears) with moderate sensorineural hearing loss. The results are summarized as follows: 1. In the patients with flat or gradual high frequency loss, the best fit frequency responses of custom ITCs can be determined by selective amplification methods. 2. In the patients with low frequency loss or abrupt high frequency loss, the best fit frequency responses of custom ITCs must be selected by the simulator, and then a trimmer of tone control was needed to be equipped to the ITCs. 3. The maximum output levels of ITCs were recommended to be decided by the simulator under surrounding noises. 4. Wide range adjustability of canal simulator appeared to be needed for many different kinds of hearing losses.
Eighty-two cases of malingering in the last 10 years were studied using electrocochleography or auditary brain stem response. In comparison with the former 5 years and the later 5 years, the cases of maringering increased twofold, and the objective hearing tests were performed 1.5 times. The cases over 70 years of age were also increased. The usefullness of electrocochleography and auditary brain stem response were newly recognized. Especially the detection threshold at 1 and 0.5kHz CM showed satisfactory results in the low tone area.
Ase et al. reported qualitative difference between wave I produced by ipsilateral stimulation and wave I delivered by contralateral stimulation using bone conducted ABR. In this study an attempt has been made to determine whether or not such a difference could be elicited from the examination of compound action potential that has been generated from bone conducted electrocochleography (ECochG), based on subjects with normal hearing. The results show a definite difference of the threshold, the latency-intensity function and the input-output function between the ipsilateral stimulation and the contralateral one. Increased threshold, prolonged latency and decreased amplitude of AP were among the characteristics found in the ECochG which was obtained from the contralateral stimulation. These differences between the two stimulations might have been explained not only by the interaural attenuation factor of less than 10dB, but also by the conduction time from the contralateral mastoid to the inner ear examined. Furthermore, radiated aerial sounds emitted from a bone conduction vibrator may not be ignored as one of the factors responsible for this difference. Appliciation of this study for ears with conductive hearing loss requires further assessment that includes the distortion of signals, the difference of sound energy emitted to the right and the left ear canal. the phase difference, the masking effect on air conduction as well as those factors noted in this report.