Click-evoked otoacoustic emissions (CEOAEs) and distortion product otoacoustic emissions (DPOAEs) were examined before and after increased or decreased middle-ear pressures in 4 guinea pips. A polyethylene tube was inserted through the auditory bulla, and middle-ear pressure was changed by pushing or drawing a syringe connected to the tube. CEOAEs were measured at about 70dBSPL using the ILO88, and DPOAEs were measured at f1=3.3kHz 65dBSPL and f2=4kHz 60dBSPL using home-made instruments. After increased middle-ear pressure, both total echo powers (TEPs) in CEOAEs and DPOAE amplitudes at 2 f1-f2 were decreased inversely in proportion to increased pressure. On the other hand, DPOAE amplitudes disappeared, even after minimum decreased middle ear pressure. TEPs also disappeared, except in one ear, after decreased middle-ear pressure. We conclude that both CEOAEs and DPOAEs can easily be deteriorated after middle-ear pressure changes, especially with negative middle-ear pressure, and that we need to estimate carefully both CEOAEs and DPOAEs in animal experiments.
An experimental study on recording of four kinds of auditory evoked responses, EcochG-ABR-MLR-SVR, on the sequential axis logarithmic time scale to elucidate the information of the auditory pathway. The subjects were young adults with normal hearing. EcochG was recorded at the promontory of the middle ear cavity-ipsilateral mastoid, and other three kinds of them were recorded at the vertex-ipsilateral ear. The sequential recording of EcochG and other three ere proceeded by the Micro-Vaxll minicomputer. The stimulus sounds were click, tone pip and tone burst with 770msec intervals. Analysis time was 500msec. Pass-band of filter was 0.8-3000Hz. The results were as follow: 1) The sequential recording of logarithmic time scale was able to display the components of auditory evoked responses without spoiling their characteristics. 2) In the case of obscure wave I of ABR, the sequential recording was possible to dicipher ABR correctly by using AP of EcochG instead of wave I of ABR. 3) This recording technique provides us the auditory electro-physiological aspects by the auditory pathway from the level of the inner ear to the auditory cortex.
Sequential recording of auditory brainstem response (ABR), middle latency response (MLR), and slow vertex response (SVR) was studied for stimulus, modality, interstimulus interval and location of recording. The responses were assessed using logarithmic time scales. The results were as follows: 1) With extending stimulus risetime, the early and middle components of auditory evoked potentials increased in latency. 2) With extending stimulus resetime, the early component decreased in amplitude. 3) With extending stimulus duration up to approximately 40ms, the wave P2 of SVR increased in amplitude. 4) The waves N1 and P2 of SVR increased in amplitude under randomly stimuli in comparison with the waves under lineary stimuli.
In Japan, the elderly population is increasing and age-related hearing loss is becoming more important problem. To cope with this situation, further study is necessary, such as more effective preventive method against presbycusis, more suitable rehabilitation with hearing aids, and so on. Investigation of present status of age-related hearing loss is the first step for this purpose. The Hearing Research Group (fiscal year 1993-1995), which belongs to the Research Project on Aging and Health in the Ministry of Health and Welfare of Japan, investigated the present status of age-related hearing loss of people 75 years or more. Pure tone audiometry performed in 77 males and 88 females revealed that age-related hearing loss tended to be more progressive at higher frequencies. The average and distribution of hearing level at six frequencies were reported in various age groups.
An effect of ossicular chain problems on bone conduction mechanism was studied using an bone conducted electro-cochleogram (BC-ECochG) to assess its clinical application. Patients having either congenital ossicular anomalies or otosclerosis were selected for this study. Latency of AP of BC-ECochG was found to be prolonged in the ears with disrupted ossicular chain, while the latency was noted to be shortened in the patients with stapes fixation. The difference of AP latency observed in this series may be explained by the fact that the amount of energy reaching the inner ear varied depending on the type of conductive hearing impairment of each individual. The other important factor for the latency discrepancy may be a phase relationship to the response that may be altered from the onset of the click. Given the fact that there is a wide variation in measurement of bone conducted sounds from person to person, a further study on accumulate data of the subjects with conductive disorder would be of great value in assessing the clinical application of BC-ECochG.