Comparison Between Hair Cell Losses and Permanent Threshold Shifts Produced by Three Levels of Impulse Noise

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Abstract
The cochleas of chinchillas exposed to three levels of impulse noise described in the previous abstract were examined using the surface preparation techniques and Nomarski microscopy. The cochleagrams and AER audiograms 30 days postexposure were compared. The animals exposed to 155 dB impulses showed no PTS, but all animals showed large and consistent outer hair cell (OHC) lesions at 6 to 12 mm, from the apex. All cochleas had relatively mild and varied inner hair cell (IHC) losses. The 161‐ and 166‐dB exposures produced PTS values ranging from 0 to 45 dB. The cochlea‐grams exhibited two basic types of lesions: (1) low level losses of IHC and OHC throughout the entire cochlea; (2) broad lesions of total OHC loss accompanied by less severe IHC losses. The most dramatic results are (1) complete recovery of hearing sensitivity with large cochlear lesions; (2) when there is a PTS, cochlear lesions were found in all animals; however, the exact magnitude and location are difficult to specify on the basis of the postexposure audiogram.

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