Effect of periodic rest on hearing loss and cochlear damage following exposure to noise.
Clark-WW; Bohne-BA; Boettcher-FA
J Acoust Soc Am 1987 Oct; 82(4):1253-1264
The effect of periodic rest on hearing loss and cochlear damage induced by noise exposure was studied in chinchillas. Seven chinchillas were rendered monaural by surgical destruction of the cochlea on the left side. Three of these were exposed to an octave band of noise centered at 0.5 kilohertz (kHz) having a sound pressure level of 95 decibels (dB) for 6 hours daily for 36 days. The other four animals were exposed to the same noise presented intermittently at the rate of 15 minutes per hour for 144 days. The effect on hearing sensitivity was evaluated by measuring the animals' response to 2 second 0.125 to 16.0kHz tones before, during or 1 (continuously exposed group) or 2 (intermittently exposed group) months after the end of the exposure period. After these tests the chinchillas were killed and their cochleas were removed and examined for histopathological changes. Cochlear damage was evaluated by counting the number of missing sensory cells. Both exposure protocols produced transient behavioral threshold shifts on the order of 28 to 46dB. These decreased to 19dB by day 26 of exposure in chinchillas exposed continuously and to between 7 and 11dB by day 20 in those exposed to intermittent noise. One chinchilla exposed to intermittent noise showed a secondary loss of sensitivity in the 3.35 to 6.7kHz region after about 60 days of exposure. Only minimal permanent threshold shifts were seen. Sensory cell losses averaged 28.4 and 15.3 percent in those exposed to continuous and intermittent noise, respectively. The authors conclude that intermittent noise exposure induces less temporary and permanent hearing loss and less cochlear damage than continuous exposures having the same energy.
NIOSH-Publication; NIOSH-Grant; Sensory-thresholds; Inner-ear; Noise-exposure; Anatomy; In-vivo-studies; Laboratory-animals; Histopathology; Noise-induced-hearing-loss
Journal of the Acoustical Society of America
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