Threshold recovery functions following impulse noise trauma.
Hamernik-RP; Ahroon-WA; Patterson-JA Jr.
J Acoust Soc Am 1988 Sep; 84(3):941-950
A detailed analysis of the threshold recovery functions in 118 chinchillas following audiometric tests and impulse noise exposure was undertaken. All animals were made monaural by surgical destruction of the left cochlea. Hearing thresholds were estimated at seven frequencies between 0.125 and 8.0 kilohertz in octave steps using an avoidance conditioning paradigm. Each animal received an impulse noise exposure with a peak sound pressure level between 127 and 147 decibels. The number of impulses was either 1, 10, or 100 for a given exposure. At least three distinctly different types of recovery function were noted. In type-I the initial threshold shift recovered monotonically with increasing postexposure time. In type- II, which was a delayed recovery for a period as long as 6 hours following removal from the noise, the pure tone threshold remained elevated and stable before thresholds began to follow a monotonic course of recovery. In type-III a growth function was noted in that over a period of at least 6 hours following removal from the noise, pure tone thresholds continued to worsen before they began to follow a monotonic course of recovery. At frequencies characterized by a type-III recovery process there was evidence of more permanent threshold shift (PTS), more sensory cell loss, and predictions of PTS and cell loss involved than at those frequencies which were characterized by a type-I recovery process.
NIOSH-Publication; NIOSH-Grant; Noise-induced-hearing-loss; Animal-studies; Cell-damage; Noise-exposure; Ear-disorders; Industrial-noise; Impulse-noise; Hearing-loss
Journal of the Acoustical Society of America
Communicative Disorders & Scis Research Foundation of Suny P O Box 9 Albany, N Y 12201