As it is suggested that cochlear damage by low frequency sound exposure is caused by the exhausting effect of inner ear metabolism, the authors investigated the effect of low frequency sound exposure on the cochlea by using EP, which is related intimately to the inner ear energy metabolism. Results were as follows: 1) Exposure of 80Hz & 120dB (SPL) caused DC-fall, but DC-rise of EP was not observed in our experiment. 2) The decline time course of EP by asphyxic anoxia delayed significantly by the exposure of 125Hz & 120dB (SPL). 3) In our experiment the decline time course of EP by asphyxic anoxia is supposed to be influenced through autonomic nervous system by exposure of the sound.
Auditory brain stem responses were recorded in 72 ears of 40 premature infants, who had no intracranial complications or neurological disorders, We examined the relation of the latency between wave I and wave I-V. Furthermore, the influences of asphyxia, apnea attack and hyperbilirubinemia to the latency of ABR were investigated. As the results, the latency of the wave I was not affected by these disorders. However the latency of the wave I was significantly elongated at 28-30 weeks of the conceptional age (C. A.), and it decreased from 35-36 weeks C. A to 41-42 weeks C. A.. This results may show that peripheral auditory organs grow into full development from around 35 weeks. The wave I-V latency was not affected by asphxia and hyperbilirubinemia. In premature infants, who did not develop apnea attack, the latency of wave I-V was almost constantly 5.0msec and showed no decrease during 31 to 42 weeks C. A. On the other hand, in premature infants, who had apnea attack, the latencies of wave I-V wave were significantly prolonged at 28-30 weeks C. A and decreased by 37-38 weeks C. A. At 37-38 weeks C. A, the latency of ABR showed no diffarence between apnea attack and non-apnea attack groups.
Hearing aid fittness on forty five hearing impaired patients over sixty years old were studied. The age distribution showed seven in the sixth decade, twenty-three in the seventh decade, and twenty-five in the eighth decade. The hearing impairment was classified into sensorineural hearing loss in 33 persons and combined hearing loss in 12. Three persons of sensorineural hearing loss were suffered from middle ear infection. Hearing aid was effective in all persons in the sixth decade, 92% in the seventh decade, and 74% in the eighth decade. The younger the persons used hearing aid the more effective and the longer hours in a day. Three out of forty-five complained of that hearing aid was less effective, and they used it few times in a week. The hearing aids were most frequently and effectively used during conversation between a person and a person in 94%, during shopping in 66%, watching TV and walking in a street in 600%. In a family, most of conversation with hearing aid were made to spouse. Outside of family, the neighbours were the most frequently made a companion of the hearing impaired with hearing aid. As a conclusion, the doctors should much more make contact with and explain of the function and limitation of hearing aid to the hearing impaired.
A 35-year-old woman with Kearns-Shy syndrome first noted a hearing loss at the age of 32, and the first hearing test was perfomed at age of 35. A pure tone audiometry showed a moderate sensorineural hearing loss in the right ear and a severe sensorineural hearing loss in the left. Békésy audiogram showed Jerger's type II pattern. Auditory brainstem responses were difficult to detct in the right ear because of involuntary movement, but latency and threshold of wave V showed fairly good relationship with the pure tone audiogram in the right. CM, SP and AP findings obtained by E. Co. G. showed the same relationship with the results of pure tone audiometry. After 10 months, her right hearing loss suddenly progressed and E. CoG. findings showed severe cochlear damage. It was determimed that the right cochlea might be damaged by Kearns-Shy syndrome.
We studied auditory brainstem responses (ABR) in 50 comatous patients (610 recordings). Findings of ABRs were classified in four groups and the results were as follows: 1. Normal responses (20 patients, 3 of them died (15%)) 2. Decrease in amplitude (8 patients, 3 of them died (38%)) 3. Prolongation of latency of the later components (5 patients, 3 of them died (60%)) 4. Absence of the responses or recognition of only an early component (17 patients, 16 of them died (94%)). Our findings suggest that ABR is a reliable diagnostic tool for predicting the outcome of comatous patients.
A simple auditory test has been developed to assist in determing whether a young hearing-impaired child can perceive spectral aspects of speech or only gross time/intensity acoustic patterns. This recorded tape-cards test required the child with optimum hearing aid to identify counted sequences and individual numbers. It was administered to 53 children (96 ears), 4-11 years old, with mean hearing levels (500, 1000, 2000Hz) at 75-133dB. As the results, scores were related to mean HL, and generally the scores were high for mean hearing levels better than 90dB and low for hearing levels poorer than approximately 113dB. Although a range from minimum to maximum was obtained for children with audiograms at 91-111dB. Their audiogram could be inadequate for diagnostic purpose of listening skills. The Japanese Auditory Number Test (JANT) is recommended for practical evaluation of listening skills and speech perception in young hearing impaired children to aid in the planning of an auditory training program.
Electro-cochleogram was recorded in the guinea pig by applying ultrasonic vibration signal (98.8 and 143.5kHz) to the cochlea. With the round window electrode, two different anoxia labile responses were recorded and identified to be SP and AP. CM was detected in the differentially recorded (SV-ST) responses from the basal turn but not from the second turn. This electrode placement revealed that the major generator of the potentials induced by ultrasound situated in the basal turn. Comparing the ultrasonic evoked response with the click evoked one, the former had a more prominent SP and steeper input-output function curve than the latter. However, no essential difference was found between them. We came to the following conclusions. 1) The guinea pig cochlea can perceive the “ultrasonic” vibration signal with frequency of far beyond the behavioural upper limit, and this seems to be an animal model of human ultrasonic perception (USP). 2) It was confirmed that there is no ultrasonicspecialized sensory cell in the cochlea but the cochlear hair cells in the basal turn take part in the USP in the guinea pig. 3) This model can be available for the further investigation of the USP.
The waves of ABR consist of several successive wavelets (fast waves) and positive slow wave. The fast waves cannot be used for objective audiometric tool because they are induced by an onset part of stimuli and lack for frequency specificity. The positive slow wave, however, is originated in a different way from the fast waves. In order to investigate the origin and the characteristics of the slow wave, experimental studies were performed in rats, and the following results were obtained. (1) The positive slow wave was elongated as the duration of a tone burst was increased. The elongated part might be more frequency specific than the fast waves because the former was more masked by a narrow band noise than the latter. (2) Depth electrode recordings demonstrated that the long durated negative potentials were obtained at the auditory nerve, the cochlear nucleus and the superior olivary complex, and positive potentials corresponding to these negative potentials could be recorded at the vicinity of the nuclei. This sustained negative potential was not observed in the inferior colliculus. Considering these results, the positive sustained potential of ABR might have its generators in the lower part of the auditory pathway such as the auditory nerve, the cochlear nucleus and the superior olivary complex.