Effects of periodic rest on cochlear damage and hearing loss.
Noise-induced hearing loss. Dancer AL, Henderson D, Salvi RJ, Hamernik RP, eds. St. Louis, MO: Mosby Year Book, 1991 Sep; :445-455
The occurrence of threshold recovery after intermittent exposure to high and low frequency bands of noise was investigated in behaviorally trained chinchillas. Animals were exposed to an octave band of noise centered at 4.0 or 0.715 kilohertz (kHz), with an octave band level of 86 decibels (dB) for 6 hours (hr) per day for 36 days, 72 days, or for 15 minutes/hr for 144days. Threshold shifts (TS) were measured 1 and 18hr after the day's exposure. In animals exposed for 36days, TSs of 40 to 55dB 1hr after exposure were observed over the first 5 to 10 days, with recovery of 10 to 17dB in the last 10 days. The 18hr post exposure tests showed a decrease in TS recovery from the first 10 days to the last 10 days. Permanent TS (PTS) of 15 to 20dB were measured after the end of the 36 day period. Small basal turn lesions were observed. The malleus/incus complex was removed at 36 days from animals undergoing 72 day exposure. Animals exposed to 0.715kHz had TS of 10 to 15dB following ossicular removal. No changes were seen in exposed animals after ossicular removal at 3.35, 4.0, or 4.8kHz. Animals exposed to 5.7kHz developed a 10dB TS shift after 37 to 41 days that continued through 72 days. A TS was also noted in 5.7kHz exposed animals after ossicular removal. No elevation in TS was observed after ossicular removal in animals exposed for 15 minute/hr intervals. TSs for animals exposed to 0.715kHz increased after 40 days and were significantly higher from 80 to 110 days than from 20 to 50 days. No recovery of threshold comparable with the 6hr/day exposure was observed. Negative TSs of 4 to 13dB from initial values were seen at the end of the experiment. The authors conclude that threshold recovery occurs during rest periods of both low and high frequency noise exposure.
NIOSH-Grant; Noise-induced-hearing-loss; Hearing-loss; Hearing-threshold; Laboratory-animals; In-vivo-study; Noise-exposure; Noise-frequencies; Noise-levels
Research Central Inst for the Deaf 818 South Euclid St Louis, MO 63110
Dancer-AL; Henderson-D; Salvi-RJ; Hamernik-RP
Noise-induced hearing loss
Central Institute for the Deaf, Saint Louis, Missouri