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Year : 2012  |  Volume : 14  |  Issue : 56  |  Page : 28--31

Amplitude changes in otoacoustic emissions after exposure to industrial noise

Mohammad Hossein Baradarnfar1, Kayvan Karamifar2, Amir Houshang Mehrparvar3, Abolfazl Mollasadeghi3, Marjan Gharavi3, Ghasem Karimi1, Mohammad Reza Vahidy1, Amin Baradarnfar4, Mehrdad Mostaghaci3,  
1 Department of Otolaryngology, Head and Neck Surgery, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
2 Industrial Medicine Department, Iran Petroleum Industry Health Organization, Tehran, Iran
3 Department of Occupational Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
4 Department of Otolaryngology, Tehran University of Medical Sciences, Tehran, Iran

Correspondence Address:
Amir Houshang Mehrparvar
Department of Occupational Medicine Clinic, Shahid Rahnamoun Hospital, Farrokhi Ave, Yazd
Iran

Abstract

Noise-induced hearing loss (NIHL) is a frequent problem in industrial settings, especially where a high noise level is present. It is permanent, and irreversible, but preventable. Routine audiometry (an objective and time consuming) test is used for NIHL screening. Otoacoustic emissions (OAEs) are recently proposed as a more sensitive test for early diagnosis of NIHL. In this study, we aimed to compare the results of pure tone audiometry (PTA) with OAE in the diagnosis of NIHL. In a cross-sectional study on 120 workers (in three groups: Not exposed to noise, exposed to noise without NIHL and exposed to noise with NIHL), we compared the results of PTA and OAE. OAE can detect some changes in the function of hearing system in subjects exposed to noise, and these changes are apparently prior to hearing loss, which is diagnosed by PTA. OAE is a more sensitive method for the early diagnosis of cochlear damage than PTA, and can be performed in industrial settings for NIHL screening.



How to cite this article:
Baradarnfar MH, Karamifar K, Mehrparvar AH, Mollasadeghi A, Gharavi M, Karimi G, Vahidy MR, Baradarnfar A, Mostaghaci M. Amplitude changes in otoacoustic emissions after exposure to industrial noise.Noise Health 2012;14:28-31


How to cite this URL:
Baradarnfar MH, Karamifar K, Mehrparvar AH, Mollasadeghi A, Gharavi M, Karimi G, Vahidy MR, Baradarnfar A, Mostaghaci M. Amplitude changes in otoacoustic emissions after exposure to industrial noise. Noise Health [serial online] 2012 [cited 2020 Aug 11 ];14:28-31
Available from: http://www.noiseandhealth.org/text.asp?2012/14/56/28/93329


Full Text

 Introduction



Noise-induced hearing loss (NIHL) is a frequent problem in industrial settings, especially where a high noise level (more than 85 dBA) is present. Noise has deleterious effects on health and performance, including NIHL. [1] NIHL is the second most common form of acquired hearing loss, after presbycusis. [2] NIHL is permanent, irreversible, but preventable. [2]

The Hearing Conservation Program (HCP) of Occupational Safety and Health Association (OSHA) mandates audiometric assessment of workers who are exposed to noise levels equal to or more than 85 dBA on an 8-h time-weighted average. [3]

Routine audiometric testing is performed periodically among workers exposed to noise higher than 85 dB. OSHA regulations require testing at the frequencies of 500, 1000, 2000, 3000, 4000 and 6000 Hz. [2] NIHL mostly affects high frequencies (i.e., 4000 and 6000 Hz). Early diagnosis of NIHL can help us prevent more hearing loss and extension of hearing loss to speech frequencies (i.e., 500, 1000, 2000 and 3000 Hz).

Pure tone audiometry (PTA) is a subjective test and needs the patient's cooperation and an acoustic chamber as well. This test cannot differentiate between sensory and neural causes of hearing loss. [4]

Otoacoustic emissions (OAE) include low-intensity signals that are emitted from outer hair cells in response to an acoustic stimulus, and can be recorded in the external ear canal. Presence of OAE shows that the cochlear outer hair cells are healthy. [5]

There are two types of evoked OAEs: Transient-evoked OAE (TEOAE) and distortion-product OAE (DPOAE). [6]

OAE is an objective test that does not need acoustic chamber and can be performed faster than PTA. Absence of OAE shows a sensory cause for hearing loss. [5],[7] OAE has been useful in some areas of hearing assessment, particularly in the newborn screening program. [8] Outer hair cells in the organ of Corti are the most sensitive parts to the noise in the ear; therefore, recently, it is postulated that OAE can play a role as a screening test for early detection of changes in these cells before any visible change in PTA.

Some studies have assessed the effect of noise on the hearing system by OAE and compared it with PTA. These studies have shown that OAE can find hearing loss in an early stage before it is obvious in PTA. [9],[10] Studies have shown a higher sensitivity of OAE than PTA for the diagnosis of individuals with a high sensitivity to noise. [11],[12]

The present study was conducted in order to compare the sensitivity of OAE with PTA for early diagnosis of NIHL in workers exposed to a high level of noise.

 Methods



This is a cross-sectional study on the workers of the tile industry during a 1-year period from 1 October 2007 till 1 October 2008 in Yazd, Iran. Subjects were selected from two groups of workers: 40 office workers (80 ears) without exposure to industrial noise (group 1) and 80 industrial workers exposed to more than 85 dB noise. These subjects were exposed to a continuous noise, with an average intensity of 92 dB. The subjects of this group were subdivided into two groups: 42 workers (84 ears) free from hearing loss (group 2) and 38 subjects (76 ears) suffering from NIHL (group 3).

After considering the exclusion criteria (conductive hearing loss, history of ototoxic drug use and history of ototoxic substance exposure, smoking and alcohol consumption), 120 subjects were selected randomly from four tile and ceramic factories. Two subjects with conductive hearing loss, 12 smokers and one subject with history of ototoxic drug consumption were excluded and new subjects entered in the study. At first, a form including demographic data and occupational history was filled for each subject. Then, their ears were examined for the presence of wax or any other conductive disorder, and then, tympanometry, pure-tone audiometry, TEOAE and DPOAE were performed for each subject. Audiometry was performed by an audiologist in an acoustic chamber meeting the standards of ANSI 2004 [13] using a clinical audiometer (AC40, Interacoustic, Denmark, headphone: TDH39) for frequencies of 500, 1000, 2000, 3000, 4000, 6000 and 8000 Hz.

Tympanometry was performed with the Capella (Madsen, Denmark). OAE was elicited with the Capella (Madsen) in the fast screen mode in a silent room by an audiologist. Clicks of TEOAE were presented in 2080 times in a nonlinear paradigm at 80 dB sound pressure level (SPL). Clicks were elicited by pulses of 40/s duration presented at a rate of 20/s. DPOAE was recorded by the DPgram method. The f 2 /f 1 ratio was held at 1.2. The stimuli levels were held constant at L 1 =65 dB SPL and L 2 =55 dB SPL. The level amplitude and signal to noise ratio (SNR) of the DPOAE occurring at 2f 1 -f 2 frequency were measured with f 2 frequency in half-octave-band frequencies of 1, 2, 3, 4, 6 and 8 KHz.

We defined NIHL as a sensorineural, bilateral hearing loss, with the hearing threshold higher than 15 dB at least at one of these frequencies: 3000, 4000 and 6000 Hz. [6]

Then, using SPSS (ver. 18), we analyzed data by the Chi square and T-tests. Level of significance was set at 0.05. An informed consent was filled for each subject.

 Results



One hundred and twenty subjects (240 ears) entered the study. They were categorized into groups. [Table 1] shows the descriptive statistics of these three groups.{Table 1}

[Table 2] shows the mean hearing threshold among the subjects of the three groups and the comparison of the hearing threshold between groups 1 and 2 and between groups 1 and 3.{Table 2}

Subjects in groups 1 and 2 had normal hearing in all frequencies in PTA, but there was a statistically significant difference between group 1 and group 3 in frequencies of 3000, 4000 and 6000 Hz in both ears [Table 2].

[Figure 1] and [Figure 2] show the results of average level of TEOAE in each ear in the three groups. Although the PTA did not show a significant difference between groups 1 and 2, there was a statistically significant difference in TEOAE results between the first and second groups in the right and left ears (P<0.001 for each ear) and between the first and third groups in the right and left ears (P<0.001 for each ear) as well. There was no statistically significant difference between the second and third groups in the right and left ears (P=0.51 and P=0.67 for the right and left ear, respectively).

[Figure 3] and [Figure 4] show the results of DPOAE in both ears. There was a statistically significant difference between the first and second groups (P<0.001 for each frequency except for 500 Hz in each ear) and between the first and third groups (P<0.001 for each frequency except for 500 Hz in each ear) as well.{Figure 1}{Figure 2}{Figure 3}{Figure 4}

 Discussion



Occupational hearing loss may be induced by noise, toxic substances or acoustic trauma. Occupational hearing loss due to noise is one of the most common occupational diseases. Audiometric evaluation of the subjects exposed to noise is a simple and inexpensive method for the diagnosis of NIHL. Now, hearing conservation programs for case finding are based on PTA. PTA is subjective, time-consuming and sensitive to surrounding noise. Therefore, there is a need for more sensitive and specific methods for early detection of NIHL. Recently, OAE has been introduced as a better predictor of occupational hearing loss, especially NIHL in workers.

OAE is a simple, fast, objective and noninvasive test, and its results are reproducible and can be recorded from each ear separately. DPOAE is very sensitive to hearing loss, and its amplitude will decrease due to different types of hearing loss. Therefore, it is used frequently for the assessment of cochlear damage due to ototoxicity, noise and Meniere disease. [14]

In this study, the results of PTA, TEOAE and DPOAE were compared in three groups: A group without exposure to noise ≥85 dBA, a group with exposure to noise ≥85 dBA that was subdivided into two groups (one group free from NIHL according to PTA results and another group with NIHL according to PTA results). We found a significant difference between the first and second groups as well as the first and third groups in response amplitude in TEOAE and DPOAE despite a nonsignificant difference in hearing threshold in PTA between the first and second groups. we showed a higher sensitivity of OAE in the diagnosis of NIHL than PTA, which was consistent with some other studies. [14],[15],[16]

Plinkert showed a higher sensitivity of TEOAE compared with DPOAE for the diagnosis of cochlear damage after impulse noise. [10]

Attias et al. compared the results of click-evoked OAE, DPOAE and PTA for the early diagnosis of NIHL in three groups of subjects (two groups exposed to noise and a control group without noise exposure). They showed a higher sensitivity and accuracy for OAE in the diagnosis and monitoring of cochlear status following noise exposure, which was consistent with our study. [15] Lapsley et al. compared PTA with OAE in the diagnosis of NIHL, and found a higher sensitivity for OAE than PTA. [16]

In another study, Viraporn et al. showed a higher sensitivity of DPOAE for the diagnosis of NIHL compared with PTA. [17]

 Conclusion



This study was consistent with previous studies to show that OAE can detect cochlear damage earlier than PTA. Therefore, it can be used in screening evaluations of workers exposed to noise more than 85 dBA. Longitudinal studies can show this issue more precisely.

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