Acoustic impedance measurements were performed on 400 ears of 188 normal neonates using the 1722 middle ear analyzer (Grason-Stadler) with a 220-Hz probe frequency. Most of the data were obtained while the neonates were asleep without anesthesia. The measurement could not be accomplished in only thirteen percent of all the ears. Sixty-five percent of the tympanograms showed an atypical AD type configuration, namely a large, smooth notched curve without a steep peak. Sixteen percent showed a double peak, and this percentage became less after the second week of life. The types of tympanograms were not correlated with the birth weight of the neonates. A clear stapedial reflex was obtained in only three percent.
Simultaneous bilateral recordings of ABR in cats were performed using binaural and monaural stimulation following the section of the eighth nerve and the auditory ascending cross pathway (cochlear nucleus-superior olivary nucleus level). The results were as follows: 1) Waves 1 and 2 seem to represent the potentials of the ipsilateral cochlear nerve and cochlear nucleus. 2) Waves 3, 4 and 5 seem to represent the potentials of the contralateral brainstem evoked potentials. 3) Wave 3 is related to the contralateral superior olivary nucleus, wave 4 to the contralateral superior olivary ascending pathway and wave 5 to the contralateral inferior colliculus. 4) In order to locate the lesions, ABR should be evaluated whether there is the response to binaural or monaural stimulation or not.
The endocochlear dc potential was recorded in normal and Kanamycin pretreated guinea pigs after Nitromin administration. In Kanamycin pretreated guinea pigs, whose Pryer reflex had already disappeared, endocochlear dc potential did not decrease at all. On the other hand, in Kanamycin pretreated guinea pigs, whose Pryer reflex remained within normal threshold, endocochlear dc potential decreased as in normal guinea pigs. These findings suggest us that organ of Corti may play an important role in the diminution of endocochlear dc potential after Nitromin administration. Kanamycin may affect on the permeability of the capillary wall for Nitromin in the cochlea. This hypothesis should be investigated in the future.
The inner hair cells isolated from the surrounding supporting cells, were observed under scanning electron microscopy (SEM). The inner hair cells arranged in one row inside of the Corti tunnel. The cuticular plate of this cell was oval, providing the stepwise-arranged sensory hairs on its surface. The portion between cuticular plate and cell body was slightly invaginated inward the cytoplasm. This invagination existed throughout the whole cell body. We would like to term it “subcuticular sulcus” according to its morphology. The cell body of the inner hair cell is not rounded, but it looks like oval shape, having a long axis parallel to an arrangement of spiral organ. Although it was said that there were the inner pharangeal cells in the inter-cellular space between the inner hair cells, SEM observations showed that they jointed each other directly in the several portions of cell body. Furthermore, SEM observation reviewed the degenerated inner hair cell with atrophic or hypertrophic cell body, and with normal sensory hairs. Those SEM findings were discussed briefly.
Out of 71 cases of familial deafness visited Kitasato University Hospital Otology Clinic, 50 cases (22 families) were transmitted by Mendelian dominance and were diagnosed as sensori-neural deafness with unknown cause. They were 19 males and 31 females, aged from 2 to 44 years. Clinical observations were performed on these 50 cases by obtaining pure tone audiograms, and the results were as follows. 1) Thirty-one cases showed high-tone loss, 13 cases showed flat or basin-shaped, and there was no low-tone deafness. 2) The threshold of high-tone was not always high in aged patients. 3) Twenty out of 29 cases under 19 years old showed good agreement with symmetry law of hereditary deafness (Langenbeck), but aged patients were devided evenly into symmetry and asymmtry group. 4) The progression of deafness did not take a certain pattern but in various ways, and the authors stressed that serial observations on each case or family might be much help in the estimate of prognosis of familial deafness.
In order to get the detailed diagnostic information from the tympanogram, we devised a new tympanometric system, in that the frequency of the probe tone changed continuously from 45Hz to 5000Hz. This system was applied to 11 subjects with normal hearing and normal ear drum. The curves of the tympanogram varied from a V-shaped in low frequencies of the probe-tone to an inverted V-shap in higher frequencies showing a W-shape in mid-frequencies, as the frequency of the probe tone was shifted. The frequency that provoked the pattern change of V to W in the tympanogram was different from subject to subject, and varied from 1400Hz to 2200Hz. Additional model experiment suggested us strongly that the stiffness of the middle ear was one of the most decisive factor in determining the frequency in which the tympanogram pattern changed its V-shape to W-shape. It was also observed that the asymmetry of the tympanogram appeared as the frequency of the probe tone increased. Several causes of this asymmetry were discussed. Further study should be performed, that is, application of this system to make a differential diagnosis for the ossicular discontinuity or the ossicular fixation.
Band-limiting experiments were performed at six test signal frequency (0.5, 1, 2, 4, 6 and 8kHz) for simultaneous, forward and backward masking. Masked threshold for a masker noise spectrum level 30dB SPL was examined as a function of the bandwidths of the bandpass, lowpass and highpass masker. The results were as follows: 1) For all test signal frequencies, the masked threshold increased with masker bandwidth at a rate of 3dB/oct and the upward spread were obtained for supracritical masker bandwidths in simultaneous masking. 2) The data for forward masking were different from the data for simultaneous masking in that the slope for subcritical bandwidths were less steep and the data for backward masking were much flatter. Despite this difference, a transition in slope could be identified at approximately the same band width for two types of nonsimultaneous masking. 3) The masker bandwidth in that the same suppression effect was obtained as a function of test signal frequency for nonsimultaneous masking were liner and proportional to critical band. These data suggested that suppression effect was possibly due to interaction of auditory filter output. 4) For backward masking, the most striking features of suppression effects were the large decrease in threshold for supracritical masker bandwidths and for intermediate intensity, and the greater suppression area of the lower frequency band than higner frequency band. These data showed also that there was much greater suppression for lower frequency band in backward masking than in forward masking. 5) These differences were consistent with hypothesis that suppression effect in forward masking was primarily determined by cochlear processes and that suppression effect in backward masking was dominated by central processes, possibly dorsal cochlear nucleus.
Auditory brain stem responses evoked by monoaurally delivered clicks were recorded in 195 ears of 103 normal neonates. The mean threshold of ABR in neonates was 25dB relative to the average subjective threshold of normal hearing adults. The latency of each peak and the inter peak latency between wave I and wave V were significantly longer than those of normal adults. The normative data including upper tolerance limits of these latencies were presented. The latencies of ABR waves in a premature infant and a brain-damaged infant were elongated comparing with these normative data. In some normal neonates, ABR were recorded every month up to 10 months after birth. There was a trend for latencies of all peaks to shorten with development, and this phenomenon was particularly pronounced for the later waves of ABR. The limited variability of ABR in normal neonates was confirmed. We believe these normative data will be useful to evaluate the hearing-functions of high-risk infants.