Wednesday, May 1, 2002

The effects of noise exposure

Noise-induced sensorineural hearing loss (NIHL) is an accepted and widely used diagnosis. However, noise-induced vestibular pathology is not. While a number of investigations have studied vestibular disturbances as the result of noise exposure, noise exposure as a causal factor leading to vestibular dysfunction is considered controversial.

Noise exposure can damage the cochlea in two ways. Loud impulse noise, such as a shotgun blast, can tear the outer hair cells (OHC), basilar membrane, and other structures, causing physical damage. Long-term exposure can cause loss of sensory and supporting cells due to metabolic changes. Both kinds of damage can result in permanent NIHL.

In order to minimize hearing loss in workers, the National Institute for Occupational Safety and Health (NIOSH) provides criteria for acceptable noise levels and exposure. NIOSH also indicates the need for additional research to study the effects of noise on tinnitus, as well as non-auditory effects such as hypertension and psychological stress. However, the relationship between noise exposure and vestibular function is not included in the group of non-auditory effects, apparently because of the lack of research in this area.

Golz, et al. (2001) studied the effects of noise on the vestibular system. The authors suggest that because of the biological and chemical similarities of the cochlea and the vbestibular system, as well as their proximity, the damage to the cochlea caused by noise exposure may also be occurring in the vestibular end organ. Furthermore, while the individual may detect the resultant hearing loss, the vestibular damage is not as noticeable because of the ability of the central nervous system to compensate for mild vestibular dysfunction. Compensation occurs more commonly with symmetric disturbances.

Patients with a significant history of noise exposure should have audiologic testing. For patients with complaints of "dizziness," balance testing may be warranted.

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