Comparative analysis of audiometric and impedancemetric findings in workers exposed to the effects of various duration industrial noise
Authors: Zivic Ljubica , Ignjatovic Snezana , Terzic Negra , Jakovljevic Vladimir , Zivic Danijela , Djonovic Nela 
Published: December 2010

Background/Aim. Industrial noise is produced in workshops due to factory machinery and tools used in technological processes. It has detrimental effect to primarily the organ of the sense of hearing, thus damaging hearing in oversensitive subjects. The aim of the study was to perform a detailed analysis of audiometric and, especially, impedancemetric parameters in workers exposed to the effects of industrial noise of various duration, as well as to determine similarities and differences in workers with differences in sensitivity to damaging effects of noise. Methods. The study included a homogenous group of 173 industrial workers involved in the same department of a huge workshop named 'Kovacica' exposed to noise level above a threshold intensity, and divided into three groups: the group I of 116 workers (232 ears) exposed to noise for 8 h in the workshop 'Kovacica', the group II of 41 workers (82 ears) exposed to noise only half of the working time, and the group III of 16 workers (32 ears) exposed to the same conditions and having the normal hearing sense. The group III served as a control group. Prior to the study any workers went through a thorough anamnesis and complete ORL examination, and then they were submitted to audiometric testing. The study included only the workers with no hearing damage due to diseases, injuries nor other detrimental factors in order to be sure that the hearing findings had been caused by industrial noise. Results. The results obtained by audiometric testing showed that 90.75% of the workers had hearing damage of various degrees, while 9.25 % of the workers had regular hearing although had been exposed to the same conditions. More severe hearing damage was revealed in the workers of the group I. Tympanometricly, in most ears of the group I workers (65.52%) a compliance value was found to be more than 0.9 cm3, while in the majority of those of the group II (59.75%) a compliance value was in the range from 0.5 to 0.9 cm3. In the workers of the group III with no hearing damage, a compliance value for any ears was in the range from 0.1 to 0.9 cm3. Mean value of threshold reflex (98.56 dB) at 500 Hz and 1 000 Hz in the group I was increased as compared with the group II (95.6 dB) and the group III (84.38 dB). At higher frequencies, 2 000 and 4 000 Hz, threshold reflex was increased in the group I (99.05 dB), and in the group II (97.6 dB) as compared with the group III (86.4 dB). The amplitude of stapedic reflex was lowest in the group I, while mean values of amplitude at 500, 1 000, 2 000 and at 4 000 Hz were 2.31, 1.38, 1 and 0.3, respectively. In the group II mean values of amplitude at 500, 1 000, 2 000 and 4 000 Hz were 2.52, 1.80, 1.30 and 0.5, respectively. In the group III mean values of amplitude at 500, 1 000, 2 000 and at 4 000 Hz were 2.36, 2.45, 2.5 and 2.08, respectively. By measuring input (rising) and output angles it was revealed that most ears of the workers in the groups I and II had rising angle ranging from 41 to 50o, and in the workers with no hearing loss from 31 to 50o. In the majority of the ears of the groups I and II outlet angle was in the range from 16 to 35o, and in the workers with no hearing damage from 26 to 35o. Conclusion. By audiometric and impedancemetric examinations it was determined that for the sense of hearing it is significant not only a threshold hearing expressed in the audiometric curve at various frequencies, but also a threshold of unpleasantness and pain under higher intensities shown by the occurrence of stapedic reflex. The less hearing field between threshold hearing and threshold acoustic reflex is, the less capabilities of hearing perception due to the occurrence of recruitment.