Temporary hearing threshold shift measured by otoacoustic emissions in subjects exposed to short-term impulse noise.

OBJECTIVES The aim of the study was to assess the influence of short-term impulse noise on the size and dynamics of temporary threshold shift, which precedes permanent threshold shift, i.e. noise-induced hearing loss. It was hoped to use the findings for preventive activities. MATERIALS AND METHODS The study included 80 healthy subjects (160 ears), aged 19-23 years, divided into two groups: group I comprised 40 recruit soldiers put to the shooting training, and group II consisted of 40 young male controls. All subjects had to show normal hearing with pure tone audiometric thresholds between 10-15 dB. Transient evoked otoacoustic emission (TOAE) measurements were performed by ILO 292 Echoport Otodynamics device 3-5 min before shooting and then 2 min, 1, 2 and 3 h, respectively after shooting. In group II the time intervals were similar. RESULTS It was found that the gunshot impulse noise from the kbk AKMS rifle caused temporary hearing threshold shift (TTS) at 1, 2, 3, 4 and 5 kHz frequencies of 1.07, 0.96, 1.41, 0.88 and 1.25 dB SPL, respectively. TIS turned out to be maximum at 4 and 5 kHz and minimum at 1 and 2 kHz. CONCLUSIONS Short-term impulse noise generated by the rifle gunshots induces rather small temporary threshold shift of hearing. Anyhow, considering possibilities of different weapon noises in the military environment as well as various sources of industrial impulse noise, the usage of hearing protectors should be highly recommended.