The origin of the negativity of the EP in anoxia is still in dispute, but the most reasonable explanation seems to be the K+ dominated diffusion potential theory. To confirm the validity of this theory, the perilymphatic space was perfused with solution with various K+ concentrations in 38 guinea pigs and the effect upon the negative EP in anoxic cochlea was examined. Although perfusion of the scala vestibuli with K+ Ringer solution ([K]: 154mM) did not exhibit any effect, the potential was elevated to 0mV when the scala tympani was perfused with the same solution. When the K+ concentration in perfusate was reduced, the elevation of the potential became less remarkable and the steady level of the EP during perfusion was closely related to K+ concentration in perfusates. The result obtained in the present study strongly suggests that the negative EP is the result of the K+ dominated diffusion potential.
This study was performed in order to explain the eneration of the so-called W-notching in tympanograms. The sound pressure changes in the ear anal were investigated along the frequency changes the probe tone using the so-called sweep freque y tympanometric system which was developped in is department. The sound pressure measured in e ear canal was increased in low frequency range d the peak of the curve of the sound pressure ange was shifted to higher frequency, as the air essure increased in the ear canal. These changes resulted in producing W-notching in tympanograms. In addition these changes can be explained by the theoretical point of view that the impedance of the middle ear increases in low frequencies and its resonant frequency shifts to higher frequency as the air pressure increases in the ear canal and the stiffness of the middle ear becomes high. The model experiment was carried out to analyse the relation between the frequency at which W-notching occured and the resonant frequency of the middle ear. This revealed that W-notching appeared at rather lower frequency than the resonant frequency of the middle ear. This is consistent with the clinical reports by Alberti or Colletti.
Eight cases with sudden deafness due to industrial noise produced by the rock drill were studied using the transtympanicelectrode technique of electrocochleography. The results obtained were as follows: All the cases showed a very rapid increase of AP amplitude with increasing click intensity in the intensity region. All the cases showed lack of the flat part (L-part) as seen in normal hearing subjects and a majority of the cases showed a higher AP output potential than those of normal hearing subjects. AP threshold were lower than that of pure tone audiogram. The amplitudes of cochlear microphonics at 4kHz and 0.5kHz were relatively well preserved. Summating potential was approximately normal value and auditory brainstem response showed normal findings. These electrocochleographical findings were persisting for a long period of time in these patients.
Measurements of psychophysical masking and suppression were performed as a function of bandwidths of the 1st masker (bandpass noise, duration 600ms and rise-fall time 10ms) and the 2nd masker (bandpass noise or white noise, duration 15ms and rise-fall time 5ms) level (N0) as a parameter. The center of the 1st masker was fixed at 2kHz and its level was fixed at 30dB SPL. The sinusoidal signal (2kHz, duration 15ms and rise-fall time 5ms) was always immediately preceded to (in the backward masking) or immediately followed by (in forward masking) the 1st masker. The signal and 2nd masker were presented simultaneously. Also the simultaneous masking was studied as a function of the 2nd masker (white noise) level. The results were as follows: 1) The amount of masking measured was about 15dB/N0=10dB in a given 2nd masker (white noise) level for simultaneous masking. These data suggested that there were much greater spatial summation at the higher masker levels. 2) At the higher 2nd masker (white noise) levels masking became increasingly prominent in subcritical band widths for backward and forward masking. The masking effect was decreased at supracritical band widths of the 1st masker. 3) At the lower 2nd masker (white noise) levels suppression became increasingly prominent at supracritical band widths of the 1st masker for backward and forward masking. 4) The suppression effect at the 1st masker bandwidth 4kHz, level differences between 1st and 2nd masker, from 10dB to 30dB increased for the forward masking, but level differences between 1st and 2nd masker, from 30dB to 50dB were increased rapidly for the backward masking. 5) The masking processes and relation between masking and suppression processes were well esta bushed for a theoriged treatment. The values of measurement were consistent with theoretical calculation.
Glycerol test for endolymphatic hydrops was erformed in 36 patients with Meniere's disease. 1) Various criteria have been used for evaluate he amount of hearing improvement as a “positive” lycerol test. We used a 20 or 30dB improvement s the limit (total amount of hearing improvement t all frequencies from 250Hz to 4kHz). The 20 B improvement was thought to be satisfactory and mple to use as a criterion for improvement. 2) The glycerol test was positive in about 50% the cases of Meniere's disease. 3) The glycerol test was diagnostic in 78% of e patients with Meniere's disease during verti nous attacks and significant hearing loss.
Three cases of psychogenic deafness in a 7-year-old and two 11-year-old girls have recently been seen in Tokai University Hospital. Two of them developed sensorineural deafness of flat type on pure tone audiograms after their mastoid processes were accidentally struck by a baseball bat or a corner of a table, but organic changes of the temporal bone were all ruled out. Because of descrepancy between pure tone thresholds and perceptive ability of conversation, psychatric investigation and assessment of auditory acuity by means of ASR and AR were performed in all three cases, and the results indicated that these children were found having a state of conflict with parents, and having psychogenic deafness. In practical point of view, ABR and AR were proved as useful for threshold determination and diagnosis of psychogenic deafness in children, and for differential diagnosis between psychogenic deafness and traumatic sensorineural deafness.
The authors designed a computerized digital filter using PDP 11/60 computer in order to increase the detectability of SVR. The methods were as follows: 1) Spectral analysis: averaged power spectrum and instantaneous spectrum of EEG were statistically estimated. 2) Digital filtering: the non-recursive digital bandpass filter using the fast Fourie transform was designed in order to detect SVR. 3) Averaging: both non-filtered and digital filtered EEG were averaged up to 100 times, and during these procedures, the avaraged EEGs of every 25 times were recorded successively, and these two modalities of averaged EEG were compared morphologically. The results were as follows: 1) Averaged power spectrum had its peak at around 3 to 5Hz, when the acoustic stimuli were clearly perceived. On the other hand, it had its peak at around 9 to 11Hz, when the acoustic stimuli were not applied to the subject. Instantaneous spectrum had its dominant energy at the delta and theta frequency bands, and was most prominent at around 300-400msec after stimuli, when the acoustic stimuli were clearly perceived. 2) The most effective pass-band of the nonrecursive digital filter in order to detect SVR was 3 to 9Hz. And SVR was closely related to damping oscillation. 3) During the whole procedure of averaging, responses were detected at some averaged sequences, on the other hand, no response was obtained at other sequences, which might be due to the variations of the background EEG, or the habituation to the acoustic stimuli. 4) The detectability of the digital filtered SVR in adults and infants were increased in comparison with the non-filtered SVR. 5) The application of this digital filter is thought to be effective in obtaining the reliable SVR.