Introduction
According to otolaryngologists, occupational noise is a
common hazard in Taiwan which leads to noise induced
hearing loss (NIHL).[1] The majority of chronic NIHL cases
are due to exposure to noise at work. Previous studies[2]
reported hearing loss is entirely preventable. In addition
to engineering controls, employers should provide their
workers with at least two means of protection – personal
protection equipment (PPE), which is the most common, and
administrative controls such as periodic shift rotation and
limiting exposure to noise when noise levels exceed 85dB.[3,4]
Because exposure to noise at the workplace is continuous,
it is important to determine the long-term effects exposure to
continuous noise has on hair cell loss. The small amount of
hair cell damage caused by exposure to intermittent noise could
be related to the recovery periods between noise phases.[5]
Several studies[6,7] have been published regarding threshold
shifts produced after repeated exposure to noise for a long
period of time; however, only a few studies have addressed
the issue of threshold shifts produced after repeated exposure
to noise for a short period of time. It is necessary to determine
whether exposure to a pulsating noise is sufficient to initiate
the recovery process. As a consequence of its effects on
reduction of continuous exposure to noise, noise-induced free
radical formation may be a significant factor in decreased
cochlear blood flow, free radical formation, and oxidative