The effect of 'conditioning' exposures on hearing loss from impulse noise.
Henselman-LW; Henderson-D; Subramaniam-M; Sallustio-V
Hear Res 1994 Jul; 78(1):1-10
The ability of conditioning exposures to protect the chinchilla cochlea against damage from subsequent exposure to a high level impulse noise was investigated. A total of 21 chinchillas were included in the study, of which seven were randomly assigned to the experimental group and 14 to the control group. All animals were made monaural by surgical destruction of the left cochlea. Evoked potential (EVP) thresholds were measured before and after the noise exposures. For conditioning, experimental animals were exposed to an octave band noise centered at 0.5 kilohertz at 95 decibels-B (dB) sound pressure level (SPL) for 6 hours per day for 10 consecutive days and then allowed to recover for 5 days. The subjects were then exposed to an impulse noise at 150dB SPL. The temporal spacing of the impulses consisted of a series of 50 pairs of impulses presented 50 milliseconds (ms) apart with 1,000ms between the onset of each pair. The total duration of exposure was about 1 minute. Control animals received only the impulse noise exposure. Following conditioning and recovery, EVP thresholds were found to be within 5dB of the baseline values. Measurements taken at 15 minutes, 24 hours, and 10 days after impulse noise exposure showed that the conditioned animals had considerably lower threshold shifts than the controls. Permanent threshold shift (PTS) was measured 4 weeks after recovery from the impulse noise; the conditioned animals showed significantly less PTS than the controls. In addition, histological examination revealed significantly less hair cell loss in the conditioned animals compared to the controls. The authors discuss the results in the context of previous studies on toughening and on the effects of impulse noise.
NIOSH-Publication; NIOSH-Grant; Noise-induced-hearing-loss; Ear-disorders; Laboratory-animals; Hearing-impairment; Protective-measures; Impulse-noise; Noise-exposure
State University of New York, Buffalo, New York