Dynamics of high-frequency hearing loss of operators of industrial ultrasonic devices.

This investigation was aimed at elucidating the dynamics of hearing loss in the range of 500 Hz to 20 kHz of 26 Ultrasonic (Uls)-operators exposed to high-frequency noise exceeding known hygienic limits. Results of audiometric tests performed twice, before and after a period of three years, were compared. The determined hearing-threshold-shift in the range of 500 Hz to 13 kHz could be explained as the effect of aging, whereas in the range of 13 to 17 kHz the stated mean threshold elevation of 2-5 dB, beyond the hearing loss connected with aging within three years, is the consequence of high-frequency noise exposure. On this basis the dynamics of high-frequency hearing loss of 1 dB/year in the case of continued exposure to high-frequency noise could be calculated. Apart from the observed threshold elevation, the fraction of ears responding to acoustic stimuli at the highest frequencies decreases by about 10% with frequency increase of 1 kHz in the range of 13 to 19 kHz. This indicates that the hearing organ is more susceptible to high-frequency noise at the highest hearing frequencies.