The time related changes of distortion-product otoacoustic emissions (DPOAEs) were examined with compound action potential (CAP) and endocochlear potential (EP) using 18 guinea pigs with surgically induced endolymphatic hydrops. DPOAEs, CAP and EP were suppressed with the postoperative time but there was a significant difference in suppression time course among these acoustic phenomena. Significant reduction in the amplitude of DPOAEs at 4 and 6kHz was already noticed at the 1st postoperative week, whereas DPOAEs at 8kHz first exhibited the suppression at the 12th week. EP recorded at the basal turn of cochlea revealed that the potential decline was already started at the 2nd week. The CAP threshold was within normal limits at the 2nd week and slightly elevation at lower frequencies (2 to 6kHz) was first recognized at the 4th week. The suppression of the DPOAEs amplitude was improved by the oral administration of isosorbide. These results indicate that the suppression of DPOAEs is a phenomenon directly related to the endolymphatic hydrops and DPOAEs are possibly the most sensitive test to detect the presence of the hydrops.
Evoked otoacoustic emissions (EOAE) were recorded from 39 ears with Meniere's disease, and the relationship between hearing thresholds, especially at a low-frequency range, and the “main frequencies”, at which the maximum power of the emissions were shown on the frequency spectra, or their changes by osmotic diuretics was mainly investigated. No obvious correlation was found between hearing thresholds at a low-or mid-frequency range and the EOAE main frequencies. In most of the ears in which EOAE main frequencies were changed by administration of osmotic diuretics, their hearing thresholds at a low-frequency range showed normal or nearly normal after administration of the diuretics. In some ears with normal or nearly normal hearing at a low-frequency range, the EOAE main frequencies changed after administration of the osmotic diuretics or before vertigo attack, even though the hearing thresholds did not change. These results suggest that some changes which could not be detected by conventional pure tone audiometry but by EOAE measurements, might occur in the cochlea by osmotic diuretics or before vertigo attack in normal or nearly normal hearing ears with Meniere's disease. It is, therefore, considered that the EOAE measurements might be useful to evaluate such changes in early stage of Meniere's disease.
Otoacoustic emissions (OAEs) are assumed to be the byproducts of power amplification of the acoustic wave on the basilar membrane. This power amplification has been called the cochlear amplifier. But there was no convincing evidence for the cochlear amplifier. The present study reports a computational model of OAEs, assuming that there is no cochlear amplifier. The slow component of evoked OAE (EOAE) was assumed to be explained by a second harmonic of Bragg reflection in a human cochlear model. The amplitude of distortionproduct OAE (DPOAE) at 2f1-f2 was estimated by computing the summation of the two primary wavelets. There was a good agreement between the theoretical predictions and the experimental results for the level behavior of DPOAE. However, the non-monotonicity in the frequency ratio function of the experimental DPOAE data was unaccountable in this meodel.
In the cases of sensorineural hearig loss, there is a good relation between hearing threshold in 1kHz and detection threshold of a slow component in evoked otoacoustic emissions (EOAE). There are same relations between EOAE and sudden deafness, and we recognized that in the cases of sudden deafness in which prognosis was good, detection threshold of EOAE was improved faster than hearing threshold. In these cases hearing become normal level. In these cases, better detection threshold of EOAE means a better prognosis of sensorineural hearing loss.
Evoked otoacoustic emissions (EOAEs) are needed to be stable from the influence of other factors to establish as an objective test of cochlear function assessment. The healthy ears of the patients with unilateral sudden deafness (SD) treated with hyper baric oxygen therapy were examined as a model of temporary middle ear conductive loss. Also the ears of healthy sides of acute unilateral facial palsy cases treated with the administration of ATP, vitamin B complex and steroids were examined as an another model. Their clinical course were studied to assess the influence on EOAEs. The minimum detectable levels of EOAEs were stable during 4 sequential weekly measurements in normal hearing subjects. Also systemic administration of the drugs in the acute cochlear deafness had no effect to EOAEs not only in a long term but in a short term. On the contrary, the minimum detectable levels of EOAEs were elevated largely in the cases with middle ear conductive loss with non-type A tympanogram. We concluded that EOAEs are an adequate test for the objective assessment to follow up cochlear function during the clinical course of acute cochlear deafness without temporary middle ear conductive loss.
Input-output functions for the slow component of evoked otoacoustic emissions (EOAEs) were studied on six normal ears with typical slow and fast components. The slow component was found to saturate at the stimulus level of about 60 dBpeSPL and at the response level of about 25 dBpeSPl. Computer simulation of EOAEs was then performed to reproduce the data using an active nonlinear model of the cochlea. The followings were inferred from the simulation: (1) irregularity of the damping of basilar membrane in a few arrayed sections such as 1.5 times higher than surrounding sections was enough to produce realistic EOAEs and (2) the saturation of EOAEs came from the nonlinearity of the active feedback mechanism of the cochlea.
We had examined pure-tone audiometries, Bekesy audiometries, tympanometries, DPOAEs of sixtythree personnels (sixty-two men and a woman) of National Defense Agency to investigate the efficacies of DPOAE as a screening method of noiseinduced hearing loss. They shoot large and/or small caliber weapons frequently. The sound pressure level of these weapons was so large that frequently their thresholds of hearing levels increased markedly at high frequency but slightly at middle or low frequencies. Their amplitudes of DPOAEs were reduced in not only high frequency but also in middle or low frequencies. This suggested that DPOAE can detect the inner ear damages caused by impulsive noise earlier than conventional hearing tests. We concluded that DPOAE measurement is efficient as a screening method of noise induced haring loss.
We observed that DPOAEs ware hardly detectable in Mongolian gerbils anesthetized with pentobarbital. On the other hand, when ketamine was used as an anesthetic, DPOAE level were generally high. The different effects of these anesthetic agents on DPOAEs became unclear when the tympanic bulla was opened. This strongly suggested that the effects might be modified by middle ear pressure. To elucidate mechanisms of the effects of these anesthetics on DPOAEs, the experiment was designed as follows; 1) investigation of ketamine effects on DPOAE in comparison with pentobarbital effects, 2) observation of the effects of middle ear pressure application on DPOAEs, 3) examinations on the influence of muscle relaxant on DPOAEs. Comparing the pentobarbital effects and effects of pressure application to the middle ear on frequency characteristics of DPOAEs, we concluded that 1) the pentobarbital administration caused negative middle ear pressure in Mongolian gerbils; 2) the generated pressure strongly suppresses DPOAEs conduction through the middle ear, thus; 3) proper selection of anesthetic agents is very important in gerbil experiments including OAE measurements.
One hundred-forty infants under 4 years old suspected of hearing loss were measured transient evoked otoacoustic-emission (TEOAE) without sadation and the results were discussed. The signal processor for ABR was converted to TEOAE measurement and stimulus was a 1.5kHz short tone burst. TEOAEs in 203 ears of 226 were easily detected the good responses in normal hearing ears without middle ear abnormalities. Though 2 cases judged as “unevaluatable” in ABR showed responses with high reproducibility in TEOAE, the response FFT in ILO-88 and following examination revealed their high tone sensorineural hearing losses. So it is the important factor in audiological evaluation of TEOAE for not only the strength and reproducibility of the responses but also the FFT analysis in TEOAE. TEOAE measurement in infants was easy, speedy and noninvasive. Moreover, the response of TEOAEs was clearly obtained with accuracy. We conclude that TEOAE is suitable examination for detection of hearing impairment and is a useful auditory screening in infants.
Twenty two members of a high school Kendoteam were examined for their hearing and evoked otoacoustic emissions (EOAE) in order to ascertain the previously-reported relationship between dip type hearing loss and continuous EOAE (C-EOAE). The measured noise level during kendo practice of kakarigeiko or a facer, “Mehn” was around 100 dBLAeq. The incidence of micro-dip positive ears in all subjects was 77.2%. The incience of C-EOAE positive ears in all subjects was 54.5%, whereas it was 67.6% in the ears with micro-dip, and 10% in the ears without. There was a significant relationship between micro-dip and C-EOAE (Q=0.90). In addition to our previous result of brass band surveys in a junior high school, the present study suggested that the C-EOAE possibly expresses a disposition of inner ear susceptibility. It was expected that EOAE measurement is useful for predicting the inner ear susceptibility to noise-induced hearing damage. Further investigation is, however, needed for verification of micro-dips as an initial sign of noiseinduced hearing damage.