The purpose of this study was to determine action sites of Salicylate by recording the acoustically evoked action potentials (APs) and the electrically evoked compound action potentials (CAPs) through the round window membrane of the guinea pigs. The acoustically evoked APs were recorded from a wire electrode placed on the round window membrane and the electrically evoked CAPs were recorded from a glass electrode inserted in the auditory nerve. Changes of amplitude in the APs and the CAPs were compared in guinea pigs before and after intravenous injections of 400mg/kg of salicylate. The suppression ratio of acoustically evoked APs at low sound intensity was significantlly greater than that of electrically evoked CAPs at low and high current levels. The findings of this study indicate that salicylate decreased the excitability of both the cochlear nerve fibers and the hair cells.
The effect of methamphetamine on auditory system was studied on guinea pigs by estimating Pinna reflex thoresholds and ABR wave changes. Methamphetamine was administered intraperitoneally to guinea pigs, and the time course of Pinna reflex threshold, latencies of waves of I, II, III, and IV, and interpeak latencies of wave I to IV, of wave I to III, and of wave III to IV of the ABR were measured respectively. The results were as follows; 1. The decrease of Pinna reflex threshold was the greatest at 30 and 66 minutes after the administration of methamphetamine. 2. The wave latencies of ABR were decreased up to 240 minutes after the administration, and the decrease of interpeak latencies of ABR was similar to the decrease of wave latencies. But, the amplitude and the threshold revealed no significant differences before and after administration of methamphetamine. These results suggest that methamphetamine has the effect of decreasing latencies of firings in both the spiral ganglion and the midbrain auditory tract. In other words, methamphetamine effects pheripheral system (spiral ganglion) as well as the central nervous system generally regarded as an effector organ.
Intraoperative auditory nerve monitoring has increasingly been used to onhance hearing preservation (HP) in the cerebropontine tumor surgery. We analyzed auditory monitoring data from 36 patients who underwent HP procedure for acoustic neurinoma, cerebropontine meningioma and epidemoid tumor during the period from 1987 to 1990. Thirty two records of intraoperative auditory brain stem response (ABR) and 18 compound action potentials (CAP) were obtained. At the end of the HP procedure, measurable waveforms were preserved in 23 of 32 patients in whom serviceable hearing was also preserved. Measurable waveforms were lost in 9 patients, but serviceable hearing was preserved in 5 of 9 patients. This fact appears inappropriate to consider ABRs as the monitoring method. CAP provided actual real-time auditory monitoring, but the placement of the electrode and maintaining contact with the auditory nerve during surgery were troublesome.
We studied directional hearing ability in 14 patients with lesions in the acoustic nerve and brain stem, and the results were compared with that of ABR's abnormality. Directional hearing ability was measured by the interaural time difference (ITD) discrimination test using a self-recording device. In five patients who discriminated ITD within 2msec., the ABRs showed unilateral abnormalities with normal I and II waves. The discrimination thresholds in these patients were from 272 to 1268μsec, and they were significantly higher than that in the control group. In nine patients who had ITD discrimination defects, the ABRs showed bilateral abnormalities or unilateral abnormalities with only low I waves. These results showed that in human the bilateral cochlear and superior olivary nuclei are important for discriminating ITD.
Intra-Uterine Sound (IUS) has been known to have an effect to soothe crying neonates. This effect has already been adopted for auditory screening of the newborns. We developed a new equipment which automatically records the response of the neonates. When the baby begins to cry, the equipment provides IUS and records his or her movement. If amplitude of the movement is markedly reduced, it is considered as responded. Forty-seven healthy newborns and 11 neonates with some perinatal disorders were examined. Each baby was tested for 12 hours and then recording was continued for another 12 hours without IUS. Among 47 healthy babies overall response rate to the IUS was 46.3% and pseudo response (spontaneous cessation of crying) rate was 24.2%. Ratio of the response rate to the pseudo-response rate was calculated for each subject. Forty-six among 47 showed the ratio greater than 1.0. A ratio of 1.6 was presumed to be an appropriate indicator for auditory screening. Among 11 babies with perinatal disorders 7 showed the ratio less than 1.6. These 7 babies were evaluated to have normal hearing by the follow-up study and they were considered to have been inadequately developed to continue crying. Developmental stage and general condition of each subject must be taken in account for the evaluation of this screening test.
We selected the Japanes words in terms of their acoustical characteristics, in order to test the close hearing abilities about children of three years and older, with the whispered voice test by pointing pictures. The results obtained were as follows: 1) Six words of group A can be heard with a clue of the acoustical characteristics at the frequencies of 2000 to 6000Hz, mainly 4000Hz. Six words of group B can be heard with a clue of that at the frequencies of 500 to 2000Hz, mainly 1000Hz. 2) Whispered voice test by using the words of group A and group B, is beneficial to screen children for low frequency hearing loss or high frequency hearing loss with normal hearing levels at another frequencies. 3) An adult male who has voice with a formant of lower frequencies is suitable for an examiner of whispered voice test.
Comfortable levels and uncomfortable levels were measured in eight adults with normal hearing, using speech sounds and pure tones as the test sounds. The comfortable levels and uncomfortable levels to the speech sounds corresponded well to those to pure tones at 1000Hz or less. The comfortableness and uncomfortableness against the levels phoneic power of speech was estimated by the subjects. In seven subjects with sensorinural hearing loss, comfortable levels and uncomfortable levels to the speech sounds given through a speaker were the same as those through a hearing aid. These results provide the useful informations to determine the gain and maximum output levels of a hearing aid appropriate for hearing of speech sounds.
A 15-year-old woman with systemic lupus erythematosus developed left lateral medullary syndrome and right internuclear ophthalmoplegia in 1987. Investigations revealed prolonged APTT, false positive serologic test for syphilis and elevated serum Ig-G, The clotting time of a 1:1 mixture of the patient's plasma and normal plasma was prolonged more than that of normal plasma alone, using the 1:5 diluted phospholipid reagent. These findings suggested that lupus anticoagulant (LAC) was responsible for development of thrombosis of the brainstem. The symptoms and signs were markedly improved by Prednisolone. In 1989, she had sudden profound sensorineural hearing loss (SNHL) in her right ear. Serologic test for syphilis was false positive and serum Ig-G was elevated again. These results and the presence of LAC imply that SNHL could be induced by thrombosis associated with LAC, although APTT was in normal range. The masking effect of daily administration of steroid from 1987 was assumed.
Hearing thresholds in 60 noise-exposed workers in a factory were measured using a high-frequency audiometer ranging from 8 to 18kHz as well as a standard one. Sixtysix per cent of the test subjects exhibited a typical dip at 4kHz (C5) and the threshold levels above 8kHz were much influenced by the degree of c5 dip. In the subjects with a C5 dip of 35dB or less, two dips or more were revealed above 8kHz with a minimal threshold shift at other frequencies. When C5 dip was 40 to 50dB, the number of a dip was single and a significant hearing loss was observed at other frequencies. In case of C5 dip of 50dB or more, the hearing was further deteriorated above 8kHz without a dip. When the hearing was a high tone loss without C5 dip in a standard audiogram, the hearing levels above 8kHz were also deteriorated with a gradual elevation of the threshold toward 18kHz. These results seems to indicate that there are chronological changes in hearing of the patients with noise induced hearing loss.
This present study is to investigate the discrimination of silent interval in hearing impaired children for the speech sound /iQta/ (normal speech sound and bandpass filtered speech sound) and the pure tone (1kHz, 2kHz), and to examine the time difference limen of silent interval. Results as follows (1) On the speech sound (/iQta/), the time difference limen of silent interval was 10-16ms (normal speech sound) and 16-20ms (bandpass filtered speech sound) in hearing impaired children, during 8-12ms and 12-18ms in normal hearing children respectively. (2) On the pure tone, the time difference limen of silent interval was 14-16ms (1kHz) and 14-18ms (2kHz), during 12-16ms and 12-16ms in normal hearing children respectively. (3) Hearing impaired children (HS1, 4) showed a tendency of increasing time difference limen than normal hearing children. On the other hand, in hearing impaired children (HS2, 3, 5), the time difference limens of normal speech sound were close upon one of normal hearing children, It is suggested that as the result of appropriate auditory learning, their hearing impaired children's auditory temporal information processing ranking is the same as normal hearing children for a given input information.
The dipole tracing of auditory evoked potentials (AEPs) was tried in 8 adults with normal hearing. The location and vector obtained by our maneuver (dipole tracing method by Nakajima, Honma 1987) showed numerous modalities. The dipole tracing of auditory brainstem response (ABR) were focused on the wave I, III and V because of their high amplitude and good reproducibility. As for slow vertex response (so called auditory evoked cortical response; SVR), P2 component (which has its peak latency at around 200msec) was investigated. AEPs were recorded with 16 electrodes placed on the scalp in according with international 10-20 method. Reference electrode was placed on the bilateral mastoid tips which were shunted. And 16 AEPs were analysed and the location and the vector of the aimed component of AEP were displayed three-dimensionally. Compared with waves I and III, wave V was usually located upward. However, waves I and III was easily influenced by artifacts and shifting of the baseline because of the small amplitude. The direction and location of the dipole with P2 component of SVR gradually changed. We could compare the locations and directions of the dipoles relatively. Since there are many parameters which influence the locations and directions of dipoles, we have to refine these parameters.
There are numerous clinical investigations on the course of hearing impairment in Meniere's disease. However, no consensus of hearing deficit can be drawn from these literatures as to the wide variations in their reports. There may be two reasons for this; firstly diagnostic criteria for Meniere's disease is equivocal and resulting in an inaccurate diagnosis, and secondly, frequencies and severeness of the disease may vary depending upon the selected patients' condition. Retrospectively the extent of hearing deteriolation was studied in 48 patients with Meniere's disease, all of whom had been followed for a period of 10 years or longer. Among these 48 cases, the hearing acuity of 25 cases were disturbed bilateraly. Moreover, in 43% of all ears hearing threshold in the speech range were less than 60dB at the final examination. Severe condition was observed in some patients bilaterally affected at the initial stage of the disease or in some patients who had early onset of the disease. Although some researchers mentioned that the early deteriolation of the hearing acuity and a halt in labyrinth functional loss and stabilization occurs in 2 to 5-10 years from the onset of the disease, deterioration of the hearing acuity in some patients occured after more than ten years had passed from the onset of their disease. However, a wide variety of the course of hearing impairment were observed in these patients. We have to follow the course of each patient carefully, and treat them adequately in an appropriate time.