In Situ Otoacoustic Emission Monitoring to Assess the Effects of Noise Exposure on Hearing Health.

Noise-induced hearing loss (NIHL) is the largest cause of action for indemnity in North American industries despite the widespread implementation of hearing conservation programs. Possible causes behind the onset of NIHL are the intervals between hearing tests which are generally too long and the tests are insufficiently sensitive to detect temporary hearing changes to act and prevent permanent hearing damage. Moreover, current noise regulations might be too lenient as to the permissible maximum noise levels. Short-interval hearing assessment could help to observe temporary changes in hearing health and prevent permanent damage. This study investigates the short-term effects of noise exposure characteristics using repeated measurements of otoacoustic emission (OAE) growth functions and presents the most significant predictors of hearing health changes as observed in sixteen individuals equipped with OAE earpieces. The experimental results of this study show that the impulsiveness and frequency spectrum of the noise level could be a possible cause of the decline in OAE levels. As a consequence, hearing conservation programs should consider taking these noise metrics into account for proper NIHL risk assessment. Such noise exposure and hearing health monitoring could greatly improve hearing conservation practices in the workplace by acting faster and eventually mitigate occupational hearing loss.

Method for protected noise exposure level assessment under an in-ear hearing protection device: a pilot study.

OBJECTIVE: To properly measure the effective noise exposure level of workers with hearing protection devices (HPD), the use of in-ear noise dosimeters (IEND) is increasing. Commercial IENDs typically feature one in-ear microphone that captures all noises inside the ear and do not discriminate the residual noise in the earcanal from wearer-induced disturbances (WID) to calculate the in-ear sound pressure levels (SPL). A method to alleviate this particular issue with IENDs and calculate the hearing protection level on-site is therefore proposed. DESIGN: The sound captured by an outer-ear microphone is filtered with the modelled HPD transfer function to estimate the in-ear SPL, this way part of the WIDs mostly captured by the in-ear microphone can be rejected from the SPL. The level of protection provided by the earplugs can then be estimated from the difference between in-ear and outer-ear SPLs. The proposed method is validated by comparing the outcome of the proposed WID rejection method to a reference method. STUDY SAMPLE: The detailed methods are assessed on audio recordings from 16 industrial workers monitored for up to 4 days. RESULTS: The merits of the proposed WID rejection approach are discussed in terms of residual SPL and hearing protection level estimation accuracy. CONCLUSIONS: Based on the findings, a method to integrate the proposed WID rejection algorithm in future IENDs is suggested.

Field Monitoring of Otoacoustic Emissions During Noise Exposure: Pilot Study in Controlled Environment.

PURPOSE: In spite of all the efforts to implement workplace hearing conservation programs, noise-induced hearing loss remains the leading cause of disability for North American workers. Nonetheless, an individual's susceptibility to noise-induced hearing loss can be estimated by monitoring changes in hearing status in relation to the level of ambient noise exposure. The purpose of this study was to validate an approach that could improve workplace hearing conservation practices. The approach was developed using a portable and robust system designed for noisy environments and consisted of taking continuous measurements with high temporal resolution of the health status of the inner ear using otoacoustic emissions (OAEs). METHOD: A pilot study was conducted in a laboratory, exposing human subjects to industrial noise recordings at realistic levels. In parallel, OAEs were measured periodically using the designed OAE system as well as with a commercially available OAE system, used as a reference. RESULTS: Variations in OAE levels were analyzed and discussed along with the limitations of the reference and designed systems. CONCLUSIONS: This study demonstrates that the monitoring of an individual's OAEs could be useful in monitoring temporary changes in hearing status induced by exposure to ambient noise and could be considered as a new tool for effective hearing conservation programs in the workplace.