騒音性難聴におけるｄｉｐの位置とその成因についての一考察

Abstract

It has generally been agreed that the industrial deafness is characterized by the hearing loss of dip type at 4 kHz, so-called c5 dip, in the early stage of the deafness. When the hearing tests were to be made at each 1 kHz on either side of 4 kHz, however, the hearing pattern of so-called c5 dip which was shown clearly on the octave audiogram disappears so often and the accurate locations of the dip could occur at 5 kHz or 6 kHz. In short, it was reconfirmed through this observation that the early dip was found not only at 4 kHz but also frequently at 5 kHz or 6 kHz, as already reported by some investigators. Then, it is indispensable to measure the hearing thresholds at 5kHz and 6kHz for the early diagnosis and control of the industrial deafness. Furthermore, it should be emphasized that the term "c5 dip" is replaced by the term "high frequency dip". As the origin of inducing high frequency dip, the vaso-constriction of cochlear blood vessels which present the sympatheticotonic condition by chronic exposure to the intense sounds seems to be the most possible factor. At present, the vascular hypothesis has been put forward as the most reliable one, attributing the origin of the dip to the chronic blood flow disturbance at the operating area of basilar membrane which corresponds with the dip frequency. From the anatomical viewpoint, it would possibly be suggested that the blood flow disturbance is liable to occur at the anastomosing region between the cochlear proper artery and the cochlear branch of vestibulo-cochlear artery.(ABSTRACT TRUNCATED AT 250 WORDS)