Energy-independent factors influencing noise-induced hearing loss in the chinchilla model.
The effects on hearing and the sensory cell population of four continuous, non-Gaussian noise exposures each having an A-weighted L(eq)=100 dB SPL were compared to the effects of an energy-equivalent Gaussian noise. The non-Gaussian noise conditions were characterized by the statistical metric, kurtosis (beta), computed on the unfiltered, beta(t), and the filtered, beta(f), time-domain signals. The chinchilla (n=58) was used as the animal model. Hearing thresholds were estimated using auditory-evoked potentials (AEP) recorded from the inferior colliculus and sensory cell populations were obtained from surface preparation histology. Despite equivalent exposure energies, the four non-Gaussian conditions produced considerably greater hearing and sensory cell loss than did the Gaussian condition. The magnitude of this excess trauma produced by the non-Gaussian noise was dependent on the frequency content, but not on the average energy content of the impacts which gave the noise its non-Gaussian character. These results indicate that beta(t) is an appropriate index of the increased hazard of exposure to non-Gaussian noises and that beta(f) may be useful in the prediction of the place-specific additional outer hair cell loss produced by non-Gaussian exposures. The results also suggest that energy-based metrics, while necessary for the prediction of noise-induced hearing loss, are not sufficient.
Hamernik
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Auditory Research Laboratory, State University of New York, Plattsburgh 12901, USA. roger.hamernik@plattsburgh.edu
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D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D002682:Chinchilla; D004734:Energy Metabolism; D005072:Evoked Potentials, Auditory / Q000502:physiology; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D009622:Noise / Q000009:adverse effects*; D016011:Normal Distribution; D011897:Random Allocation