Workers' health care of the Matsushita Electric Industrial Company is administrated by Matsushita Health Administration Center and the health administration sections are founded in all factories. The Division of Industrial Hygiene, which is a part of the administration center, has many businesses included periodical audiometric testing of all employees exposed to noise and management of workers with hearing disorder. The data of 12 factories indicated that percentagee of workers exposed to noise in plant is different from 0.8% to 29.2%. In the exposed groups 2.5% to 40% showed changes in hearing thresholdss at 4kHz and 2kHz. Hearing loss would become evident after more prolonged noise exposure and the elevation of threshold is aggravated by the increased magnitude of exposed noise. The countermesures of hearing conservation from noise are restricted by various factors, but in programs, periodical hearing test is more free from the restriction. Hearing test is efffctive to the prevention, detection and management of hearing impairment.
In this paper we presented 6 cases of malingering. The patients' age ranged from 40 to 60 years old and five of them were female. Indemnity after traffic accidents seemed to be psychogenic motive in four females and an financial reimbursement of welfare annuity in one female. The cause of malingering in the male patient was an injury inoccured on his job accident. All of these cases were detected by the repeated standard audiometry and other tests ERA was applied for obtaining threshold of hearing loss in two cases. In general, it is necessary to distinguish deaf person due to psychosomatic reaction from malinger who volitionally adopts the role of deafness for purpose of his own. However, it, practically, is very difficult to make differential diagnosis between them.
In 51 patients with acoustic trauma, hearing test and equilibrium test were conducted. In the audiogram, gradual form of high tone loss was seen most frequently, followed by abrupt form of high tone loss, dip form and flat form. In Békésy audiometry, type II of Jerger was frequently encountered. In the eqilibrium test, central and peripheral dizziness as well as dizziness of unknown origin was noted. In animal experiment, guinea pigs were exposed to 100dB (SPL) at 4, 000Hz 12 hours a day for consecutive 40 days. The degenerative change was found in the full turn particularly around the first half of the second turn of the organ of Gorti in the cochlea. As the vestibular injury, atrophic changes were noted in the sensory epithelium of the saccular membrane, urticular membrane and semicircular canals. Mild thickening of the cerebral artery is noted. In clinical cases, angiography revealed stenosis of vertebral and vertebrobasilar arteries. These were due to hypertension and abnormal lipid metabolism secondary to autonomic nerve imbalance and pituitary-adrenal hyperfunction.
On the occurrence of noise deafness, the significance of conductive deafness has been discussed from the various angles, and very different opinions have been emphasized respectively by the different authors. In this observation, 21 workers with unilateral conductive deafness were selected from 419 workers who have been worked in the noisy environment of Japanese National Railways. Among of the selected cases, the clear sign of noise deafness was proved in either or both sides in 16 cases. On these 16 cases, the comparison of the hearing pattern between both side was made in order to evaluate the effect of conductive deafness upon the occurrence of noise deafness. In most cases, no sign of the noise deafness wasf ound in the side at which the ear has the conductive lesion for a long time of period. From this result, it can be said that the conductive deafness shows the so-called ear-plug effect and might be a defensive factor to the occurrence of noise deafness. However, in a few cases, whose ears have been exposed to an intense noise with severe vibration, the sign of noise deafness was proved also in the side of conductive lesion. This might indicate that the conductive deafness rather accelerates the occurrence of noise deafness under the noisy environment with intensive vibration.
In 308 ears which cleary showed noise-induced impariment, the continuous audiometry was made by using a Békésy type audiometer. On the continuous audiogram, the dip didn't always appear at 4KHz and the dip at 5KHz was found as frequent as at 4KHz. In most ears, the extent of hearing loss to the lower frequency range was limited to 2.5KHz and very few ears with marked hearing loss extending over the frequency limit of 2KHz were proved only of the long term workers. It has already been agreed generally that the threshold at 8KHz is so much unstable and is markedly affected with age-factor. To the profound noise deafness or the aged workers, the fourfold division method has a danger of underor overestimating the individual hearing level of noise deafness. Then, it is better to exclude the threshold at 2 and 8KHz for taking the avarage of hearing level in noise deafness. In order to evaluate the hearing level of noise deafness exactly, the mean value of threshold at 3, 4, 5, and 6KHz is rather serviceable to prevent of miscalculating the hearing level in noise deafness than the so-called fourfold division method.