Attenuation and protection provided by ossicular removal.
J Acoust Soc Am 1987 Apr; 81(4):1093-1099
The behaviorally measured attenuation produced by removing the malleus and incus in the chinchilla was investigated. An evaluation was made of the protection provided by this procedure for ears that were exposed to noise levels, durations, and spectra that have been standard in the laboratory. Chinchillas raised in a noise shielded colony were used. Four of seven chinchillas were trained to report thresholds for pure tones and frequency modulated signals. Ossicular removal was performed on one side of each chinchilla. Chinchillas were exposed to an octave band of noise (OBN) at 0.5 or 4.0 kilohertz (kHz) at a sound pressure level (SPL) of 95 or 108 decibels (dB) for up to 216 days. The total percent of missing cells for the entire cochlea was noted. In most cases, the hair cell losses on the exposed side exceeded those produced in ears with ossicular removal. The findings indicated that ossicular removal is a safe, efficient method for producing a conductive hearing loss in the chinchilla. Behaviorally measured attenuation provided by ossicular removal varied from 41dB at 0.125kHz to 81dB at 4.8kHz and averaged 60dB. The conductive hearing loss provided by ossicular removal insures monaural testing for losses up to 5dB, yet retained the unexposed ear as a control. Ears which were protected by ossicular removal were not damaged by exposures to an OBN centered at 0.5kHz at levels of at least 95dB SPL or to an OBN centered at 4.0kHz for levels of at least 108dB SPL.
NIOSH-Publication; NIOSH-Grant; Noise-induced-hearing-loss; Ear-disorders; Hearing-loss; Laboratory-animals; Noise-exposure
Research Central Inst for the Deaf 818 South Euclid St Louis, MO 63110
Journal of the Acoustical Society of America
Central Institute for the Deaf, Saint Louis, Missouri