1983 年 26 巻 5 号 p. 589-598
Hearing acuity of 103 tank crews of the Self Defence Forces in the Fuji Educational Division were measured by pure tone audiometry and Békésy audiometry fixed frequency tracing at 4000 Hz. The crews were asked by questionnaire if they had any otologic symptoms, eg. tinnitus, stuffy feeling, autophonia, and hearing difficulty.
All examinees were male and their age distribution was between 19 to 49 years. All of them have been exposed to tank-machine noise at the level of 80-95 dBSPL (C), and bombardment sounds 500 times a year at the peak level of 150 dBSPL (C) since they enlisted at 18 years of age.
Stuffy feeing was reported by 8.2%, of them, autophonia by 8.2%, continuous tinnitus by 38.5% and 44.9% complained of being hard of hearing c5 dip of more than 30 dB was seen in 26 subjects and a sharp decline of more than 40 dB at 8000 Hz appeared in 17 ears of 12 subjects.
A combination of c5 dip in one ear and sharp decline on the other was seen in 2 subjects.
After subtracting the level of the aging component of hearing loss, the percentage of occurrence of hearing loss at 4000 Hz became extremely high when their employment period exceeded five years. In spite of their marked hearing loss at 4000 Hz, the fluctuation in continuous traceing in Békésy audiometry narrowed only in a few examinees.