Hearing threshold shifts from repeated 6-h daily exposure to impact noise.
Hamernik-RP; Ahroon-WA; Davis-RI; Lei-F
J Acoust Soc Am 1994 Jan; 95(1):444-453
The behavior of hearing threshold shifts (TS) following interrupted daily exposures to impact noise was investigated, and whether the intermittency of an exposure affects the magnitude of permanent threshold shifts (PTS) and sensory cell loss produced by exposures of equivalent energy was determined. Twenty four monaural chinchillas were exposed to either 107, 113, 119, or 125 decibel (dB) impacts for a 6 hour period daily repeated for 20 days. Three groups of three animals each were exposed to the same impacts having the same total energy, but on a noninterrupted schedule of 24 hours per day for 5 days. Preexposure and 30 day postexposure pure tone hearing thresholds were measured at various octave intervals. Also a single threshold determination was made immediately prior to each daily exposure and immediately after each exposure. After testing, histological analyses of the right auditory bulla were performed. The results demonstrated that TS following exposure to broadband impacts can recover more than 30 dB despite continuing exposure to the noise. The magnitude and time course of the recovery of TS was dependent on the audiometric test frequency and the exposure energy. Interrupted exposure produced less trauma, as measured by PTS and sensory cell losses, than the equal energy uninterrupted exposure. The correlations between the measures of trauma and the behavior of the TS of an animal suggest that animals not exhibiting the toughening effect may be more susceptible to noise damage.
NIOSH-Publication; NIOSH-Grant; Noise-induced-hearing-loss; Noise-exposure; Laboratory-animals; Noise-frequencies; Noise-protection; Occupational-exposure
Communicative Disorders & Scis Research Foundation of Suny P O Box 9 Albany, N Y 12201
Journal of the Acoustical Society of America
State University of New York at Buffalo, Buffalo, New York