One hundred and sixty-eight patients with sudden deafness visiting Nagasaki University Hospital were examined by electrocochleography (ECochG). There is a very close relationship between detection threshold of cochlear microphonics (CM) and the hearing level at the final stage of the disease, irrespectively to the time of examination. It is likely that the detection threshold of CM is determined by the severity of impairment of hair cells at an early stage of disease. Therefore, CM responses also allow one to predict how much the hearing can be improved, no matter at what stage of the disease ECochG is performed.
The stimulated oto-acoustic emission (OAE) has peen investigated by stimulations of tone-bursts at frequencies between 1.0kHz and 2.0kHz because resonance frequencies of a mechano-acoustical characteristics of the recording system existed in this frequency area. In an effort to investigate the function of cochlear micromechanics in cochlear partitions in a wider range, we recorded OAE evoked by stimulations of tone-bursts at frequencies between 0.5kHz and 4.0kHz, and the emission cochleogram in this frequency area was investigated in 27 ears with normal hearing and type A tympanogram. The results obtained were as follows: (1) No clear OAE was evoked by the stimulation of tone-burst at 0.5kHz in all ears. However, clear OAEs were evoked by stimulations of tone-bursts at frequencies between 1.0kHz and 4.0kHz in almost all ears and the emission cochleogram in this frequency area was obtained in each ear. (2) The configuration of emission cochleogram in each ear showed the convex type, the high tone gradual loss type or the high tone abrupt loss type. The averaged emission cochleogram in 27 ears showed the configuration of the convex type with a peak at 2.0kHz. (3) The analysis of emission cochleogram could be used to investigate the function of cochlear micromechanics in cochlear partitions in a wider range, and therefore it could increase the usefulness of OAE as the clinical tool to investigate the cochlear function.
We reported that the ear with spontaneous OAE tended to prolong in an evoked OAE measurement. No subject with prolonged EOAE felt tinnitus during the examination. This prolongation of EOAE was ovserved easily by stimulation with same or higher frequency than SOAE frequency. The wave of EOAE synchronized with stimulating tone shortly after stimulation onset (-10ms), and later was transformed to synchronize with SOAE (12ms-). We supposed that this synchronization with SOAE was the prolonged EOAE. And it was speculated that the stimulation with higher frequency than SOAE oscillated the shorter point than SOAE point on the basilar membrane, and later gave the energy to oscillate the basilar membrane in phase with SOAE.
Consonant confusion study was performed in a patient with a Nucleus multiple electrode Cochlear implant. Discrimination between voiced and unvoiced was successful, but conausions occured in voiced plosives, voiced fricatives, nasals, and unvoiced plosives, respectively. Discharges of the cochlear implant electrodes for the japanese vowel-consonant-vowel sillables were digitally recorded. And discharge patterns for consonants were compared with their sound spectrograms. Discharges of electrode #20 were always observed in voiced consonants, but not in unveiced. They were thought to correspond to buzz bars in spectrograms. Recognition of voiced or unvoiced may be helped by discharges of electrode #20. In plosives, the confusions may be caused by poor electrode discharges at the plosive portion of spectrograms. In some voiced consonants, discharges were seen which did not have the corresponding components in their original spectrograms. In order to make the consonant discrimination better, a new speech processing strategy should be developed which have more fidelity to temporal and frequencial properties of consonants.
Binaural interaction (BI) in auditory 49-Hz steady state responses (SSR) was investigated in 13 adult subjects with normal hearing. Two kinds of SSR were recorded mostly during sleep. They were elicited with sinusoidally amplitude-modulated tones at 500Hz or with tone-pips of 2-1-2 cycles at the same frequency. Auditory brainstem response (ABR) and middle latency response (MLR) to the same tone-pips were also recorded at a stimulus interval of 115ms. BI was represented numerically in the ratio in amplitudes of binaurally evoked responses to summed monaural responses for the two ears. The mean values of BI measured from ABR, MLR (Pa component), SSR elicited with amplitude-modulated tones and with tone-pips were 0.945, 0.773, 0.898 and 0.871, respectively. Significant difference was found between the BI-values in MLR (Pa) and each of other 3 responses. Lack of significant difference in the BI-values between SSRs and ABR strongly suggested that ABR was the most important component in SSR during sleep.
Speech sound perception of 16 patients with Nucleus Cochlear Implant was investigated using videotaped materials specially designed for evaluation of the patients. For monosyllable sounds, the recognition in the conaition cochlear implant alone or of lipreading alone did not correlate to that of cochlear implant plus lipreading. For words, the recognition in cochlear implant alone condition highly correlated with that of the cochlear implant plus lipreading. The auditory and the visual informations were mutually complementary for monosyllable sound recognition, whereas the auditory signal provided major information for word recogonition, in that the visual signal seemed to be not only supplemental but more active in sematic identity.
Oto-acoustic emission evoked by bone conduction stimulation (BC-OAE) was investigated in 12 normal hearing ears with type A tympanogram and was compared with that evoked by air conduction stimulation (AC-OAE). The bone conduction stimulation was given at the forehead. The stimulus sounds were tone bursts at five frequencies between 1.0kHz and 4.0kHz. The results obtained were as follows: 1) The BC-OAE was obtained at all five frequencies in all 12 ears. 2) The frequency of BC-OAE was almost the same to the stimulus frequency. 3) The mean pseudothreshold of BC-OAE was lower than that of AC-OAE elicited from the ipsilateral ear at all five frequencies. 4) The intersubject variation of pseudothreshold of BC-OAE was smaller than that of AC-OAE. 5) The interaural difference of pseudothreshold of BC-OAE was less than 5dB in 80% of the recordings. 6) Emission cochleogram of BC-OAE in each ear showed the configuration of the convex type, the high tone gradual loss type or the high tone abrupt loss type. The averaged emission cochleogram showed the configuration of the high tone abrupt loss type. The intersubject variation of emission cochleogram of BC-OAE was smaller than that of AC-OAE. 7) The AC-OAE elicited from the contralateral ear could be evoked by the bone conduction stimulation due to the similar mechanism as the shadow hearing in psychoacoustic audiometry.
Glycerol test was performed in 182 ears with definite and suspected Meniere's disease in about 8 years. Intravenous administration of 10% glycerol (500ml) for 2 hours was adopted instead of oral administration. Various criteria of glycerol test have been proposed since Klockhoff and Lindblom pablished their first report in 1966. We used only pure tone audiometry and proposed an adequate criteria in our new method, and also discussed the difference between oral and intravenous administration of glycerol from view points of blood concentration of glycerol, serum osmorality and side effects. From our clinical observations, it was concluded that the intravenously administered glycerol test is greatly useful method for detection of endolymphatic hydrops. Moreover, in view of the criterion it was strongly recommended at least 10dB inprovement in pure tone threshold at two or more frequencies as the significantly positive test.
Auditory threshold shift for air conduction following various air pressure changes in the external auditory canal was examined. The obtained figure was named “tympanoaudiogram”. It was applied for normal subjects and patients with middle ear diseases. The results were compared with tympanogram. When artificial static air pressure (positive or negative pressures) was established in the ear canal of normal subjects, hearing attenuation was observed in low and middle frequencies. The curve was similar with the theoretical curve for increased stiffness of the tympanic membrane. Thus, 250Hz threshold curve as a function of air pressure change was similar with the shape of A type tympanogram. Tympanoaudiograms in the patients with congenital incudostapedial disconnection slowed an absolutely different pattern, although conventional tympanogram showed A or Ad types. Thresholds were elevated by +200mmH2O, however, marked threshold gains were measured by -200mmH2O in low and middle frequency tones. Differences in the threshold levels between +200 and -200mmH2O were 26 to 39dB in 250Hz. Further study should be performed to clarify the mechanism of these results. However, they indicate that this test can be of value in differential diagnosis of the ossicular diseases.