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    Focusing in: Noise impact on hearing loss



    Story by Megan Mudersbach 

    Naval Medical Research Unit Dayton

    By: Dr. Andrew Keebaugh

    Protecting United States service members from noise-induced hearing loss is an ongoing focus of the Department of Defense as hearing loss is the number one disability among veterans. Noise exposure in the military can occur 24 hours a day, such as during flight operations, even in off-duty areas. For example, noise measurements in berthing areas of aircraft carriers have been found to exceed current hearing protection standards during flight operations, bringing into question what constitutes acceptable noise levels during off-duty periods following occupational noise exposures. More research is needed to understand what level of noise is sufficient during daily “effective quiet” periods that would allow for auditory recovery and prevent permanent hearing loss.

    Researchers from Naval Medical Research Unit - Dayton’s (NAMRU-Dayton) Environmental Health Effects Laboratory (EHEL) are evaluating the impact of military-relevant 24 hour noise exposures on hearing loss.

    A project funded by the Navy In-House Laboratory Independent Research Program (ILIR) is studying the effects of elevated steady noise levels during a recovery period (simulating the off-duty shipboard environment) after an eight hour high noise exposure at the occupational limit of 85 decibels time-weighted average. These noise exposures would not be expected to cause damage on their own, but in combination could impede auditory recovery and lead to permanent hearing loss after four weeks of exposure.

    A separate study funded by the Defense Health Agency (DHA/J9) is focusing on the effects of steady and impulse noise exposures during the daily recovery period following occupationally relevant exposures to combined noise and inhaled chemical exposures.

    There are many factors that can complicate risk assessment when it comes to noise exposure. Noise exposure itself is often complex and may consist of brief high-level noise impulses, in addition to steady elevated noise levels. Additionally, breathing in certain chemicals, such as the volatile organic compounds (VOCs) present in jet fuel, may worsen noise-induced hearing loss. It is unknown how these complex noise and chemical exposures will impact permanent changes in hearing, especially taking into account elevated noise levels during the auditory recovery period.

    NAMRU-Dayton is currently developing a system that can study steady and impulse noise exposure for 24 hours a day with or without chemical exposure for a portion of that time. A noise generation system had been developed for prior studies at the lab, but the system was limited to use with short-term exposure chambers and could only generate steady noise. EHEL toxicologist, Dr. Andrew Keebaugh, is working with Captain Lester Morales, a student at the Air Force Institute of Technology, to design and construct a noise exposure system capable of generating high-decibel impulse noise for use in these studies.

    We are also expanding our auditory testing capability to conduct functional assessments of peripheral and central hearing. Dr. Rachel Howes, an audiologist, recently joined the NAMRU-Dayton team to assist EHEL with audiology measurements and analysis.

    The research team at EHEL is committed to protecting our service members from noise-induced hearing loss by using our unique facilities to support the effort.

    For more information visit us at and follow us on Facebook @NavalMedicalResearchUnitDayton and Twitter @NAMRUDayton.



    Date Taken: 07.31.2018
    Date Posted: 07.31.2018 20:22
    Story ID: 286654

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