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The effect of exposure level on the development of progressive resistance to noise.

Subramaniam M; Campo P; Henderson D
Hear Res 1991 Mar; 52(1):181-188
The effect of exposure level on the development of progressive resistance to noise exposure was studied in chinchillas. Adult chinchillas with stereotaxically implanted colliculus recording electrodes were exposed to 85, 95, or 100 decibel (dB) octave band noise centered about 0.5 kilohertz (kHz) 6 hours/day for 10 days. Hearing thresholds in response to 0.5 to 16kHz signals were determined before and after each daily exposure. Any trends in the magnitude of the shifts over the 10 day period were noted. The largest threshold shifts occurred within the first 2 days in the 95 and 100dB groups. The magnitude of these shifts tended to become smaller on later days except at 16kHz. Maximum threshold shifts in animals exposed to 85dB noise did not generally occur until after 2 to 4 days of exposure. When analyzed by signal frequency, the most pronounced decreases in threshold shift after repeat exposure to 85dB noise occurred at 0.5 and 2kHz. At 4 and 8kHz 85dB animals did not develop an initial threshold shift or demonstrated little change in threshold shift upon repeat exposure. At 16kHz 85dB animals did not develop a threshold shift. Animals exposed to 95 and 100dB noise revealed large threshold shifts initially at 4 and 8KHz. These shifts were significantly attenuated after 10 days of exposure. The 95 and 100dB groups revealed large threshold shifts at 16kHz which were not significantly attenuated by repeat exposure. The authors conclude that the decreases in threshold shift induced by repeat exposure to 85, 95, or 100dB octave noise depends on exposure level and the frequency of the test signals. The resistance to noise, as manifested by attenuations in the threshold shift, is not easily explained by conventional ideas of noise induced hearing loss and may be due to more than one mechanism.
NIOSH-Publication; NIOSH-Grant; In-vivo-studies; Laboratory-animals; Hearing-threshold; Noise-induced-hearing-loss; Physiological-response; Adaptation; Acoustical-measurements; Noise-exposure; Author Keywords: Threshold shift; Exposure level; Toughening
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Hearing Research
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State University of New York, Buffalo, New York
Page last reviewed: June 12, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division