放射線の内耳に及ぼす影響

Abstract

Since the beginning of the 20th century, it has been known that the radiation can cause hearing loss, but the details of this process are not as well known as those of radiation effects on other organs.The anther studied the effects of single dose of x-ray irradiation on the inner ear of guinea pigs by continuously measurement of cochlear microphonics (CM) and auditory brainstem responses (ABR) with permanent electrodes implanted on the round window and in the skull. With 2, 000, 4, 000, and 6, 000 rad, slight conductive hearing impairment was observed in some guinea pigs. Severe sensorineural hearing loss was acutely induced by irradiation more than 8, 000 rad. After 10, 000 rad irradiation, both CM and ABR to air and bone conduction stimuli were usually enhanced by 20-50% above the pre-irradiation levels for one or two hours after completion of the irradiation, and they disappeared simultaneously about 6 hours after irradiation.Hearing impairment began earlier with increase in irradiation: about 10 hours at 8, 000 rad, about 6 hours at 10, 000 rad, and about 3 hours at 12, 000 rad.Responses to high frequency sounds generally disappeared slightly earlier than those to low frequencies.The I-III interpeak latency of ABR didn't change after 10, 000 rad irradiation.Endocochlear potential (EP) drop to about 30mV was observed about 7 hours after 10, 000 rad irradiation.In the scanning electron micrographs, the sensory hairs in the outer and inner hair cells of every turn seemed to be normal 6 hours after 10, 000 rad irradiation.In transmission electron microscopy, however, heavy damages were seen at the outer hair cells in the basal coil of the cochlea.