[Effect of noise on changes in the acoustic reflex]

Acoustic, stapedial reflex represents a response of the m. stapedius to a sonic excitation of supra speech intensity. It is the constitutive part of impendancmetric investigations, it is performed on the same apparatus after tympanometry, and it is the inseparable part in representation of impendancmetric findings. Until now, the most frequently monitored parameters of acoustic reflex of clinical importance are: threshold, amplitude, output and input angle of the reflex curve. The aim of this work was to performed detailed analysis of mentioned parameters in workers exposed to extensive action of industrial noise of known physical characteristics (of different durations) and to establish which changes occurred in these workers, to what extent and under which conditions. Investigations included 173 industrial workers (346 ears), which work in working unit "Forge", where during the working process noise is produced which is above permissible limits and of the unfavorable frequency content. Workers were divided into two groups. The first group consisted of workers who were spending the whole working time in the workroom with noise above permissible limits, the second group consisted of workers who were spending 3 hours of the working time in that workroom, while the control group consisted of workers who were spending the whole working time in that workroom but they did not have any hearing impairment. Workers of the first and the second group had the hearing impairment, which occurred exclusively as a consequence of chronical acoustic trauma. For all the workers the anamnesis was taken, as well as ORL status and audiometric and impendancmetric investigations were performed, namely the tympanometry and acoustic reflex. Results have shown that the acoustic reflex threshold at 500 Hz and at 1000 Hz for the first group (95.10 dB) was increased with respect to the reflex threshold of the second and the control group (84 dB). At higher frequencies of 2000 Hz and 4000 Hz an increase of the reflex threshold was found for the first and the second group (96 dB) with respect to the control group (87 dB). The amplitude of acoustic reflex was increased, at frequencies 500 Hz and 1000 Hz (3.38), with respect to the second group (2.78) and the control group (2.36), and at higher frequencies, this increase is more prominent. The input angle of the reflex curve was, for the first and the second group, within limits 41 degrees to 50 degrees, and for the control group was from 31 degrees to 50 degrees. The output angle was, at majority of ears of the first and the second group, from 26 degrees to 35 degrees, and for the control group it was from 16 degrees to 35 degrees. Acoustic reflex, as the noninvasive method, short term one, objective and simple for application, does not require collaboration of workers, what provides for objectivity of obtained results and what caused that wrongful estimations, impressions and subjective reactions of workers were avoided.