Among hearing impaired children wearing hearing aids, some of them showed aggravation of hearing loss. The factors of the aggravation were investigated, and the following conclusions were found. 1) The aggravation of hearing loss by hearing aids were a) resulted from gain even less than 40dB. In order to control maximum output sound pressure, Automatic Recruitment Control or Peek Clipping, etc. were needed in hearing aids because the cause is thought to be excessive input sound pressure. b) easily happened soon after hearing aids were changed. c) able to occure not only in ears with hearing aids but also in the opposite ears. 2) When the aggravation were found, the interruption of using hearing aids was valuable. 3) In order to find the aggravation earlier, the frequent hearing tests should be performed on the children wearing hearing aids.
Middle latency response (MLR) of cats was recorded from an electrode on the vertex referred to the ear lobe under general anesthesia with nembutal. The procedures of this experiment were as follow. Variation of MLR was investigated by several recording parameters. The influence of muscle relaxants was examined. Click and several kinds of tone bursts were applied to cats, and six different filter-bands were used, and furthermore, the reliability of the MLR was examined, especially in the low intensity stimuli, by test-retest recordings. Finally the changes of MLR were experimented when the brain was destructed at the level of the superior colliculi. The result were as follows. 1) The cat's MLR was closely similar to that of human. 2) The muscle relaxants had little influence to the recording of MLR. 3) MLR was detected by using narrow filterbands, for example, 0.3-30Hz, 1/sec of stimulusinterval and abrupt rise time of the stimulus sounds. 4) MLR was quite reliable at the high intensity stimulus level, however, quite variable at around the response-threshold intensity level. 5) MLR was disappeared immediately after destruction of the brain at the level of the superior colliculi.
Analysis of slow vertex responses (SVR) of the infants evoked by acoustic stimuli was carried out under a series of computarized procedures. These procedures were, 1. averaged power spectra of the EEG, 2. power spectrum of the averaged EEG, 3. amplitude histogram of the averaged EEG, with or without acoustic stimuli. Results; 1. Averaged power spectra were supposedly useful for objective identification of the SVR, however, power spectrum of the averaged EEG and amplitude histogram showed little significance on the evalution of SVR. 2. Power in δ frequency band was appropriate as the index for the objective judgement of SVR. 3. SVR may be understood to be positive when the power in δ frequency band is over 60%, and negative when it is under 50%. The evaluation of the SVR is not clear when the power in δ frequency band is between 50% and 60%.
Pathologic changes in the tympano-ossicular chain and mucous membrane of the middle ear cavity were histopathologically examined on the horizontal and frontal serial celloidin sections from the 110 human temporal bones in age ranging from new born to 82 years. The results were as follows: 1) Inflammatory changes such as fibrous thickening and adhesion of mucous membrane with cell infiltration in the middle ear cavity were found in 95.5%. 2) The changes relating to otitis media were as follows; (a) Fibrous thickening more than 100μ (69%), focal calcification, retraction and fibrous adhesion, rupture and complete destruction (0.9%) of the tympanic membrane, (b) Slight resorption of the cortex of the ossicles, circumscribed resorption in the tip of the crus longum of the incus (41.7%) and complete destruction of the ossicles (0.9%), (c) Fibrous thickening including excessive proliferation of the mucous membrane of the middle ear cavity associated with irregular narrowing of the cavity (10.9%), 3) The changes relating to aging were as follows; (a) Regressive changes of the articular cartilage of the ossicles, (b) Progressive decrease in thickness of the annular ligament resulting in impaction of the foot plate of the stapes to the margin of the vestibular window in 11.8% over 30 years old. 4) Congenital ankylosis of the head of the malleus with the bony wall of the epitympanum occurred in 0.9%. 5) Infiltration of metastatic carcinoma (4.6%) and leukemic cells (11.8%) in the external ear canal, middle ear, and bone marrow, resulting in occasional destruction of the structure of the conductive system. 6) Development of the functional structure of the ossicular chain was considered dependent on mechanical stimulation in transmission of sound pressure.
The present study was performed to clarify the injuries of the auditory organs and their pathogenesis in the Hartley guinea pigs and rabbits exposed to experimental explosion of gunpowder, 5.5, 10 and 15kg. The results were as follows. 1) The hearing in the guinea pigs after exposure to the explosion were classified into three types according to the pinna reflex, the site of the injury in the auditory organ and degree of the injury. Type I, conductive deafness, abrupt missing of the pinna reflex in the total frequencies tested. Type II, predominantly perceptive deafness, gradual missing of the pinna reflex in the frequencies tested, and Type III, no missing of the pinna reflex and no injury of the inner ear. 2) There was distinct difference in degree of the injury of the ear between in the guinea pigs and rabbits. 3) The guinea pigs placed outside a shield-room showed Type I, conductive deafness and those placed inside the shield-room showed Type II, perceptive deafness or Type III, no missing of the pinna reflex. 4) Type I and II hearing impairment and the irregular extent of the damage of the inner ear suggest that the damage of the inner ear was caused by the intensive transient atmospheric pressure during explosion which was transmitted by the tympano-ossicular chain to the inner ear.
Compairing two audiograms of the identical ear of one hundred and seventy normal subjects tested with 1 to 6 months interval, the limit of the natural error was studied. Distribution of the values obtained by subtracting the hearing threshold level of second audiogram from those of first was demonstrated. The means, standard deviations and rejection limits were calculated. In conclusion, the following values were proposed as the critical values for the decision of the hearing change, improvement or deteriorations, and it can be diagnosed that the hearing had improved or deteriorated when the values obtained by using the above mentioned manner exceed the followings.
The threshold shift due to torsion of the neck in cases with C5-dip after head injury or acoustic trauma was discussed. In cases of head injury with C5-dip, the changes of the auditory threshold were recognized in 10 cases of 11 cases. In cases of acoustic trauma with C5-dip, the change of the auditory threshold above 6dB was not recognized in all of 12 cases.