In 20 subjects of noise-induced deafness in whom hearing tests were conducted yearly for 10 years after they left their noisy workshop, changes in hearing were studied and the results were as followes. 1) Their hearing after leave from their noisy workshop showed a decline almost equal to changes with aging in terms of both frequency and average hearing loss. 2) However, among these 20 cases during the course of study one case had little change in hearing and the other showed further decline in hearing. 3) Various frequencies and the average hearing loss were studied in all the subjects. The results of the study showed that there is little difference of hearing in each subject, and that their hearing loss progresses gradually.
Auditory evoked fields (AEFs) were recorded in responses to vowel sounds and the A note of a violin from normal adults by means of SQUID magnetometer and the following results were obtained; (1) AEF over specific portions of the scalp has the morphology similar to that of auditory evoked potential. (2) Morphologies of AEFs are much sensitive to the measuring positions and AEF has rich information about the spatial distribution of generators in the brain. (3) Remarkable activities of equivalent current dipole generated by synchronous excitations of a set of neurons are found in or near the primary auditory cortex during the latency range of N1-P2 complex of slow vertex response. (4) AEF detection is much useful for the estimation of the location of generators in the brain.
The effects of vanadate (Na3VO4) on endocochlear DC potential (EP) and cochlear microphonics (CM) were studied at the basal turn of guinea pig cochlea and its distribution in the cochlea was observed with an electron probe microanalyzer (EPMA). The results obtained were as follows; 1. With perfusion of vanadate solution from the scala tympani, EP showed a transient overshoot and then a gradual decrease. 2. With the perfusion from scala vestibuli, EP showed a rapid decrease without an overshoot. The decrease of EP was time and dose dependent of vanadate perfusion. 3. With anoxic anoxia, negative EP was recognized and its negative potential level was decreased by longer perfusion. 4. Cochlear microphonic potentials showed a decrease in parallel with the decrease of EP. 5. By the histolagical study with EPMA, abundant accumulation of vanadate was recognized at the stria vascularis and also at the Corti's organ. 6. From the results obtained, it is concluded that vanadate inhibits the electrogenic pump at the stria vascularis and also inhibits the hair cells of Corti's organ.
ABR findings in two patients with vertebrobasilar insufficiencies and intraoperative ABR monitoring in one patient with bilateral vertebral artery stenosis were presented, and the diagnostic value of ABR for the estimation of progressive brainstem ischemia was discussed. Our conclusions were summarized as follows; 1) ABR was of useful for estimating states or levels of ischemic condition of the brainstem, especially of the vertebral artery areas. 2) In parallel with the progression of ischemic stage, the first reduction of all wave amplitudes and then delayed wave V and increased I-V interpeaks were occured. However, when the blood flow being recovered, the above changing patterns were gradually disappeared and completely recovered into normal pattern. 3) Ipsilateral ABR responses were more significant for estimating laterality of the brainstem function.
The effects of inhalation anesthetics (enflurane, halothane, nitrous oxide) and hyperventilation on brainstem auditory evoked responses (BAER) were studied in 52 patients underwent lower abdominal surgeries with spinal continuous peridural anesthesia, that was able to exclude noxious stimuli of the surgical procedures. Under normothermic, normocapnic and normotensive status, with increasing end-tidal concentration of enflurane and halothane, the interpeak latencies (IPL) I-II, III-V and I-V increased with a linear dose-related manner. While, with nitrous oxide (66%), IPL I-III increased, but IPL III-V didn't change. This results showed that enflurane and halothane influenced the auditory pathway from the acoustic nerve to the thalamus with a linear dose-related manner. However, nitrous oxide was different from halogenized agents, such as enflurane and halothane, in the effects on the brainstem. Under hyperventilation (PaCO2 30-25mmHg) with 1.0% enflurane, IPL I-V increased significantly in comparison with normoventilation (PaCO2 45-35mmHg). High concentratian of enflurane with hyperventilation should be given carefully, bacause BAER latency delay was considered to be related with seizure activity of enflurane.
The etiology of sudden deafness is not yet known. Thus, proper evaluation of the validity of its treatment is important in order to elucidate the pathogenesis of this desease. The deafness is characterized by the fact that spontaneous recovery is quite common. Based on the statistical analysis of the data from 625 cases of sudden deafness (1974-1985), it was revealed that the following factors were of prognostic importance; ie. time after the onset, hearing level and pattern of the audiogram at the initial visit and presence of the vestibular symptoms. In this study, the author established the criteria which were necessary to predict the prognosis of the sudden deafness. In addition, the relationship between the factors mentioned above and cure rate, degree of improvement of threshold and the fixed hearing level was examined, and the validity of various treatment modalities was re-evaluated. The conclusions obstained in this study were as follows; 1. In the patients who visited our hospital within 15 days after the onset, complete recovery rate should be taken into account. 2. In those visiting later than 16 days after the onset, prognosis should be based on the degree of improvement of hearing level. 3. In evaluating the patients only on the basis of “time after the onset”, at least 51 cases are necessary for statistical analysis. 4. For the patients who visited us within 8 days after the onset, no treatment modalities were regarded as effective which include administrations of steroids, low molecular dextran, urografin, ATP compounds or vitamins, and stellate ganglion block.