In order to study the electrophysiological features of vibration syndrome, so-called white wax disease, 37 patients (74 ears) with white wax disease and normal hearing controls (19 ears) were examined by EcochG and ABR. In EcochG, N1-latency and N1-amplitude were measured and it was found that there was no significant differencies between the patients and controls. In ABR, I-V wave latencies were measured. Both IV wave latency and V wave latency of the patients increased as compared with those of controls, which suggested that there was some CNS lesion in patients with white wax disease. There were some neurootological reports suggesting the possibility of the existence of CNS lesion in white wax disease. The present report suggested its possibility which was proved electrophysiologically.
Intravenous injection of lidocaine is used to relieve tinnitus clinically. But the mechanisms of the relief of tinnitus is not yet clearly understood. There are few experiments to know the effect of lidocaine on the cochlea of animals. Since most of them aimed to show the changes of AP and CM as effects of lidocaine on the cochlea, they used much doses of lidocaine to affect the cochlea. This study was undertaken in order to elucidate the effect of this drug on the cochlea by recording the cochlear nerve spontaneous discharges which are related to tinnitus originated from the cochlea. Intravenous administration of lidocaine in the dose of 5mg/kg demonstrated no remarkable changes of the spontaneous discharge rate but that of 10mg/kg caused a temporary decresase of the spike rate of the nerve fibers ranging from 23% to 100%. It was a general tendency that decrease of spike rate in the fibers with higher spike rate was prominent in those with lower spike rate. It was concluded that intravenous administration of lidocaine acted on the cochlear nerve fiber in the way to suppress their discharge rate temorarily.
It is not yet well understood where are the acting sites of the lidocaine in the auditory system. Our previous study has shown that injection of lidocaine reduced the spontaneous discharge rate transiently in guinea pigs. This study was further aimed to elucidate the effects of lidocaine on the cochlear nerve by recording the single nerve action potentials which were evoked by electrical pulse applied to the cochlea through the round window membrane before and after intravenous injection of lidocaine. One minute after intravenous injection of lidocaine, the threshold of spikes responding to the electrical stimuli was twice as much as that of preinjection. It decreased linearly and took 36 min. for full recovery. Decrease of spontaneous discharge rate started about 10 seconds earlier than prolongation of latency of the spikes by the electrical stimuli after initiation of lidocaine injection. These results indicate that intravenous injection of lidocaine acts directly on the cochlear nerve and causes transient decrease of its excitability.
Our previous reports showed that the cochlear spontaneous discharge rate and the excitability of the nerve were decreased following injection of 10mg/kg of lidocaine to the guinea pigs with the normal cochlea. This study is aimed to know the effects of lidocaine on the impaired cochlea which was induced by injection of Aspirin. Aspirin impaires the cochlear functions and produces tinnitus and hearing loss clinically. Following injectcion of aspirin we injected 5mg/kg of lidocaine to the same guinea pigs to know the effects of lidocaine on the impaired cochlea. The cochlear spontaneous discharge rate was decreased significantly (p<0.01) following injection of 5mg/kg of lidocaine. But the minimum threshold to the tone stimuli was not changed. This dose, 5mg/kg, is the smallest among the doses which have been reported to be effective on the cochlea. Clinically tinnitus originated from the abnormal temporal pattern of interspike interval of cochlear spontaneous discharge may be relieved by intravenous injection of lidocaine which decreases the cochlear spontaneous discharge rate.
A 17-year-old girl complained of bilateral progressive deafness since age of ten. She could hear sound but could not understand speech. Pure tone audiometry showed that her hearing was fluctuating within a range of 40dB in both sides, and pure tone average was 68-86dB in the right ear, and 56-65dB in the left ear. In speech audiometry, maximum articulation score was 0% in both sides Békésy audiometry indicated type IV pattern, which seemed to be pathognomonic to a retrocochlear lesion. Reflex decay in acoustic-stapedial reflex test was positive. Audiotory brainstem response and action potential in electrocochleogram were not evoked even at the maximum stimulation level of 70dB HL. On basis of these findings, her hearing loss was suspected as of brain stem lesion due to unknown pathology.
Cockayne's syndrom in two siblings, a 11-year-old boy and a 7-year-old girl, is reported. Both children had the characteristic symptoms of Cockayne's syndrome, dwarfism, senile appearance, mental retardation, retinitis pigmentosa, calcification of bilateral basal ganglia, and sensorineural deafness. The results of auditory brainstem response audiometry demonstrated no response to 95dBHL click stimuli, and behavioral audiometries in different occasions revealed progressive hearing impairment. Both patients had fitted hearing aids, and showed developmental improvement in auditory behavior, vocalization, and language development. But after four year's follow up study, the boy showed poor activity because of progression of hearing and optic impairment. Our report suggested that in children with progressive hearing impairment, periodical evaluation and early fitting of hearing aid are important for better communication.
Hearing thresholds of COR audiometry in 59 young children with sensorineural hearing loss were compared with those of play audiometry in follow-up observation. Test frequencies were 500, 1000 and 2000Hz, and the intervals between the two tests were ranged from less than 1 year to more than 5 years. The test-retest agreement within the limits of ±15dB was achieved in 80% of the total 150 paires of thresholds. The agreement, however, decreased significantly (62.5%) when the COR audiometry was performed in young children aged less than 2 years. The difference between the average thresholds of the COR and play audiometry was only 0.2dB. The results suggested that insidious progression of deafness during the period of the tent-retest interval canceled the physiological development of hearing in infants and young children.
The most appropriate rise-decay time of tone pips for frequency-selective stimulation of auditory brain stem response (ABR) was studied using the pure tone masking technique in six adult cats. Auditory stimuli consisted of 500Hz, 1000Hz, and 2000Hz tone pips with five rise-decay times (0.5, 1, 2, 4, 8msec). ABRs were recorded using the tone pips as stimuli under masking by pure tones of various frequencies. Decrements in ABR amplitudes by pure tone masking with different frequencies were compared among five different tone pips at each frequency. The results indicated that the most appropriate rise-decay time of tone pips for frequency-selective ABR was 4msec at 500Hz, 1000Hz, and 2000Hz.
40Hz event ralated potential (40Hz-ERP) described by Galambos in 1981, has been considered as the useful method in predicting hearing threshold across the audiometric frequencies especially in adults. But, in some cases, the detection of the responses near threshold is rather difficult, because of its wave morphology. In order to solve these problems, synchrony measure method (SM), one of the phase spectral analysis described by Fridman in 1984, was applied for the automatic detection of 40Hz-ERP. The sensitivity of the SM was demonstrated in 14 normal adults 40Hz-ERP responses with different intensities (50, 30, 20, 10, 0, and -10dBSL) of ipsilateral stimuli, SM, especially component synchrony measure of 40Hz, is useful for 40Hz-ERP detection in normal adults.