title: Modeling signal-to-noise ratio of otoacoustic emissions in workers exposed to different industrial noise levels.
abstract: BACKGROUND
  Noise is considered as the most common cause of harmful physical effects in the workplace. A sound that is generated from within the inner ear is known as an otoacoustic emission (OAE). Distortion-product otoacoustic emissions (DPOAEs) assess evoked emission and hearing capacity. The aim of this study was to assess the signal-to-noise ratio in different frequencies and at different times of the shift work in workers exposed to various levels of noise. It was also aimed to provide a statistical model for signal-to-noise ratio (SNR) of OAEs in different frequencies based on the two variables of sound pressure level (SPL) and exposure time.
  
  
  METHODS
  This case-control study was conducted on 45 workers during autumn 2014. The workers were divided into three groups based on the level of noise exposure. The SNR was measured in frequencies of 1000, 2000, 3000, 4000, and 6000 Hz in both ears, and in three different time intervals during the shift work. According to the inclusion criterion, SNR of 6 dB or greater was included in the study. The analysis was performed using repeated measurements of analysis of variance, spearman correlation coefficient, and paired samples t-test.
  
  
  RESULTS
  The results showed that there was no statistically significant difference between the three exposed groups in terms of the mean values of SNR (P > 0.05). Only in signal pressure levels of 88 dBA with an interval time of 10:30-11:00 AM, there was a statistically significant difference between the right and left ears with the mean SNR values of 3000 frequency (P = 0.038). The SPL had a significant effect on the SNR in both the right and left ears (P = 0.023, P = 0.041). The effect of the duration of measurement on the SNR was statistically significant in both the right and left ears (P = 0.027, P < 0.001).
  
  
  CONCLUSIONS
  The findings of this study demonstrated that after noise exposure during the shift, SNR of OAEs reduced from the beginning to the end of the shift.
authors.affiliation: Department of Occupational Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Parvin
authors.initials: P
authors.lastname: Nassiri
authors.affiliation: Department of Occupational Health, School of Public Health, Kerman University of Medical Sciences, Kerman, Iran.
authors.forename: Sajad
authors.initials: S
authors.lastname: Zare
authors.affiliation: Department of Occupational Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Monazzam
authors.affiliation: Department of Audiology, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Akram
authors.initials: A
authors.lastname: Pourbakht
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Kamal
authors.initials: K
authors.lastname: Azam
authors.affiliation: Department of Biochemistry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Taghi
authors.initials: T
authors.lastname: Golmohammadi
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D006801:Humans; D007492:Iran; D008297:Male; D009623:Noise, Occupational; D009784:Occupational Diseases / Q000503:physiopathology*; D016273:Occupational Exposure; D017084:Otoacoustic Emissions, Spontaneous; D059629:Signal-To-Noise Ratio; D013997:Time Factors