Hearing Loss from Acoustic Energy

Excessive noise exposure is an important and usually preventable cause of hearing loss. Hearing loss can result from chronic or acute noise exposure, usually causing injury at the level of the cochlear hair cells. However, acute acoustic trauma can also cause injury to the tympanic membrane and middle ear structures.

Chronic noise exposure may be recreational or vocational. The Occupational Safety and Health Administration (OSHA) has established guidelines for safe limits for acute and chronic noise exposure to prevent occupational noise-induced hearing loss. Exposure to noise of 90 dB or less is permissible for up to 8 hours per day. As the noise intensity increases, the permissible duration of exposure decreases. OSHA outlines procedures for hearing protection and monitoring. These standards also can help provide guidelines to minimize excessive recreational noise exposure. Recreational activities known to cause excessive noise include hunting or target shooting with firearms, use of power tools or power lawn equipment, attendance at sporting venues, motor racing events, action movies, or concerts and listening to loud music on headphones. Hearing protection or avoidance is recommended for such activities.

Acute exposure to excessively loud noise can cause conductive or sensorineural hearing loss. CHL can result from a blast-type injury that leads to tympanic membrane perforation or ossicle injury. The conductive component of the hearing loss is usually reparable, but severe acoustic trauma can also cause sensorineural loss. SNHL from acute acoustic trauma is usually the result of temporary hair cell dysfunction or permanent injury, leading to transient or permanent threshold shifts, respectively. A concussive or blast injury (e.g., slap, airbag deployment to ear) can result in the formation of a labyrinthine fistula from the inner ear into the middle ear, which causes severe vertigo and SNHL. Most fistulas close spontaneously with bed rest, but some require middle ear exploration and repair. However, the sensorineural hearing loss is usually permanent.

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