The noise spectrum influence on Noise-Induced Hearing Loss prevalence in workers

Abstract

Noi se Induced Hearing Loss (NIHL) is an insidious and cumulative disease that worsens over the years with workrelated noise exposure. Aim: To evaluate the noise spectrum influence on NIHL prevalence in workers. Materials and Methods: This a cross-sectional historical cohort carried out in steel mills, lumber mills and marble shops, with noise levels above 85dB, in which we evaluated the auditory thresholds for frequencies from 250Hz to 8,000Hz. To evaluate the work environment, we observed the entire setting, aiming at checking sound intensities in an eighth frequency filter. Results: We carried out 192 hearing threshold evaluations after an occupational anamnesis. Concerning NIHL, we noticed that 49% of the audiometry results presented hearing deterioration in the acute frequencies. We studied the mean values and standard deviations for frequencies over 3,000Hz, in all workers, and we observed that the highest average values were in the frequency of 6,000Hz. We did not notice any association among frequency bands carrying intense noise levels and the hearing damage frequency. Conclusion: Noise intensity seems to be the main risk factor for loss hearing, regardless of frequency range.

Estudo do espectro sonoro nos limiares de altas frequências em trabalhadores expostos ao ruído

“…Some studies suggest that in the high frequencies there is greater auditory sensitivity with aging, when compared to the lower frequencies 23,24 . Such findings corroborate the literature and indicate that high frequency audiometry could be clinically utilized for the early diagnosis of NIHL [20][21][22] . In Brazil, NR 7 from the Ministry of Work and Labor 11 defines that the audiometric test must be always made through the frequencies from 0.5 kHz to 8 kHz; however, there is still no standardization for high frequency audiometry.…”

“…We noticed that the mean value of audiometric thresholds and the presence of a NIHL-suggestive notch 6,9,20 were significant in the high frequencies. In the present study, the prevalence of notches in the high frequencies follows that of other authors, who noticed a higher prevalence of hearing loss in the high frequencies in workers with a past of exposure to high noise levels [20][21][22] . The fact that the prevalence of the NIHL-suggestive notch is greater in the high frequencies could be explained because of the very cochlear anatomy and function dynamics, besides the lack of vascularization in the cochlear basal region 15 .…”

“…Thus, we can state that without doing the high frequency audiometry, it would not have been possible to detect the worker's hearing loss in an initial stage. Therefore, this procedure was fundamental for the early detection of the NIHL-suggestive notch; this fact has also been pointed out by other authors 2,4,6,20,22 . Having all of this, it is paramount to reassess the guidelines and parameters of the assessment required by law, whenever the goal is to promote and protect the worker's health.…”

“…Such assessment aims at protection the worker's hearing and is fundamental in Hearing Protection Programs -HPP [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . Conventional audiometry is but a graphic recording of hearing thresholds at different sound frequencies, which vary between 0.125 kHz and 8 kHz [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] . However, with the evolution of occupational audiology, recent studies have suggested the use of high frequency audiometry (above 8 kHz) as a clinical resource which adds greater sensitivity to such assessment, and provides for the early detection of cochlear problems 4,5 .…”

Evaluation of Noise-Induced Hearing Loss on the Workers of one of the Ahvaz Steel Companies

“…Also, in industrial environments, cardiovascular problems, sick absenteeism, tired employees, declining productivity, and increasing efficiency and risk of incidents along with a wide range of other indicators of physical health could be related to exposure to noise (20)(21)(22). Being continually exposed to high levels of sound pressure causes damage to the hair cells of the organ of Corte external and internal, which is associated with hearing loss (23). Studies have shown that equivalent sound pressure levels continuously for more than 8 hours of exposure are two important parameters that describe the relationship between "constant noise and hearing loss" (4,(23)(24)(25).…”