One hundred seventy six infants (296 ears) under 4 years old suspected of hearing loss in the outpatient clinic and 72 full-term neonates (106 ears) and 22 pre-term neonates (37 ears) were subjected to the measurement of evoked otoacoustic emission (EOAE). The measurement was completed without sedation in 85.8% of all inpatients. Good response in EOAE was obtained in 57.8%, 90.6%, and 89.2% in outpatient, full-term, and pre-term neonate ears, respectively. There were 37 false positives and 4 false negatives in outpatients, suggesting the need of the technical improvement and the standerization of response criteria. Further analysis on the false negative cases along with consideration of the sociomedical benefits will be required for the clinical application of EAOE infants as an audiological screening.
The evoked otoacoustic emissions (EOAEs) were recorded from 55 patients, who had been clinically diagnosed as Meniere's disease before this study, in order to determine the usefulness of EOAEs for diagnosis of Meniere's disease. EOAEs were elicitted using Otodynamic Analyzer ILO88 before and after glycerol administration and the relationship between the change in hearing level and in parameters of EOAE (TEP, Repro) was investigated. The results were as follows: 1) Although there are several reports suggesting that EOAEs could not detect the change in hearing level at low frequency area less than 500Hz, we could detect the difference in EOAEs in such frequency area in Meniere's disease. 2) There was a statistically significant difference in EOAE parameters between before and 3 hours after glycerol administration. 3) The change in hearing level and EOAE parameters in each case was not always parallel after glycerol administration. From these rerults, we concluded that the detection rate of Meniere's disease could be improved by adding EOAEs as one of the parameters in Glycerol test.
Distortion-product otoacoustic emissions (DPOAEs) at three F2 frequencies (1, 2and 4kHz) were recorded from 43 ears with idiopathic sudden deafness (ISD). The potential of DPOAEs as a clinical test to predict the hearing prognosis of ISD was investigated. At the first visit within 2 weeks after onset, DPOAEs were detected in several ears with hearing loss of 40dBHL or more at the corresponding frequencies to F2. In most of these ears, hearing at the DPOAE-detected frequencies was recovered to 30dBHL or less after treatment. The incidence of DPOAEs, however, was low in the ears with severe hearing loss and in mid-frequency range, and there were many ears in which hearing was recovered even though DPOAEs were not detected. Moreover, DPOAEs were not detected or their output was not increased before hearing was changed during the course of hearing recovery. From these results, it was considered that the prognosis seemed good in the ears with DPOAEs at an early stage of ISD, but that there were many problems and limitations for clinical application of DPOAE testing with respect to accurate and reliable prediction of prognosis.
Distortion products otoacoustic emissions (DP-OAE) were measured in normal and sensorineural hearing impaired patients with and without tinnitus in 0.5, 1, 2, 4, 8kHz (f2/f1=1.21, L1=L2=75dB SPL). In subjects with pure tone thresholds better than 25dB in 4kHz, 4kHz DP-OAE amplitudes of tinnitus sufferers were significantly lower than tinnitus free subjects. These results suggested the possibility of objective assessment of tinnitus with DP-OAE.
The speech perception performance of recipients of 22 channel cochlear implant was compared with that of patients using hearing aid. Subjects were post-lingually deafened adults including 31 patients using hearing aid and 48 recipients of cochlear implant. Speech perception test consisted of 5 bowels, 50 monosyllables, and 500 Japanese words. These test materials were heard by tape recorder. The means and standard deviations of the percentage giving the correct answer using a new coding strategy, SPEAK, were 84.8±15.0% for vowels, 34.0±17.5% for monosyllables, and 31.6±22.4% for words, and was better than those using F0 F1 F2 or MPEAK coding strategy. This speech perception ability in recipients of cochlear implant corresponded to that in patients using hearing aid with hearing level of 80-85dB. This improvement of the coding strategy indicated that it is reasonable to extend cochlear implant to post-lingually deafened adults obtaining poor benefit from hearing aid.
For evaluation of recruitment by ECochG-CM, electrocochleography was performed in 10 ears with recruitment which was found by ABLB test and self-recording audiometry, in 6 Meniere's disease patients and 4 acoustic neuroma patients. 10 ears with normal hearing were used for control. Short tone bursts with frequency of 1, 2, 4kHz were employed as acoustic stimuli to evoked ECochG-CMs and clicks were used to measure ECochG-AP. The results were as follows. 1. Elevation of CM detection thresholds was seen in all cases with recruitment. It is considered that the presence of recruitment implies cochlear deafness. But one case with acoustic neuroma revealed lower CM detection thresholds than audiometric thresholds. This means that the existence of retrocochlear deafness is not proven from psychological audiometric test. 2. At higher stimulus levels, the input-output curves of 1kHz-CM in cases showing recruitment were similar to the curves obtained from normal control. It is supposed that this finding has relevance to the recruitment on ECochG-CM. On the other hand, the AP input-output curves in cases with Meniere's disease indicate no recruitment. For assessment of recruitment input-output curves of both CM and AP are thought to be necessary.
A temporal factor in word discrimination ability of the hearing-impaired was clinically evaluated by classifying the word discrimination characteristics for variable speed speech using variable-speech-rate audiometry. The results of the study were compared with the speech reception threshold (SRT) and the speech discrimination score obtained from the standard speech audiometry authorized by the Japan Audiological Society. The subjects were 73 ears in 49 patients with sensorineural hearing impairment. The word discrimination characteristics were classified into three categories, A, B, C, according to the difference between the performance-intensity curves for normal speech rate and for 1.5 times normal speech rate. 30ears which were slightly affected by the fast speech were classified into group A. 17ears which were greatly affected by the fast speech were classified into group C. Group B consisted of 26ears which were between A and C. Since there was no close relation between SRT, speech discrimination score and the results of this audiometry, the results of this audiometry can not be estimated by the results of the standard speech audiometry. It was concluded that this examination was useful for evaluation of a temporal factor in word discrimination ability.
Currently, the promontory stimulation test (PST) is the most frequently used electrical stimulation method to confirm the level of electroneural hearing. However, since it requires to place a needle through the tympanic membrane, it is a difficult procedure to perform in infants. The recently developed silver ball electrode for infants by Med-E1, on the other hand, can perform electrical stimulation by just placing a silver ball electrode close to the tympanic membrane. By using this method, we compared it with the traditional needle electrode and evaluated the hearing of the better ear, and thus examined the possibility of clinical applications. The results of this investigation revealed that in the deaf ear, both the needle electrode and the silver ball electrode could induce a sound sensation, but the latter needed a higher electric current. Also, as with the previously reported needle electrode studies, the positive ratio was lower in the better ear. From the results, it was concluded that this method could be used to evaluate electroneural hearing in the clinical field.
Bekesy sweep audiometry and DPOAE were measured in 18 volunteers with normal hearing level. Microdips were observed in 10 subjects on Bekesy, and in 12 subjects on DP-gram. Most microdips occurred at frequencies higher than 3kHz on Bekesy, while on DP-gram at frequencies between 2 and 4kHz. The distribution of the dip frequency differed between Bekesy and DP-gram. In 10 subjects who demonstrated microdips at the first examination, a few subjects exhibited microdips at the second examination. These data suggest the presence of subclinical micro-cochlear dysfunction in volunteers with normal hearing level.
In recent years, much information is available concerning the relationship between EOAE and DPOAE and the differences in the nature of these emissions, but they have never been compared each other. The differences between recordings of DPOAE and EOAE are related to factors such as the stimulus tone, recording method, and evaluation method. We presumed that these differences made comparison of the two emissions difficult. In order to obtain simultaneous recordings of the two otoacoustic emissions and evaluate them by the same method, we developed a new procedure and assessed the effect of stimulus intensity on DPOAE and EOAE. The subjects were 5 volunteers (10 ears) with normal hearing aged 25 to 43 years. The stimuli were two synchronized short tone bursts (f1 and f2) and their rise, decay, and plateau time duration were 1 msec. EOAE data were collected with stimuli presented at a rate of 4/sec and were averaged for 250 of stimuli. The stimulus frequencies were constant (f1=2.0 and f2=2.4kHz) and the stimulus intensity was varied over the range from 0 to 70dBnHL by 10dB increments. We investigated the EOAE and DPOAE spectra under two conditions of stimulus intensity (L1 and L2), which were 1) L1 equalled L2 and 2) L1 remained constant at 30dBnHL. The results were as follows: The DPOAE spectrum was found in the averaged waveform at the same time as EOAE. These spectra were recorded clearly at a stimulus intensity ranging from 30 to 40dBnHL when L1=L2 and over a range of 30 to 40dBnHL when L1=30dBnHL. The DPOAE spectrum had almost the same modality as a function of stimulus intensity as the EOAE spectrum in this study.