Effects of high-level impulse noise intensity, number, and rate on hearing

Abstract

The effects of very low-frequency, energy-content impulse noise exposures on hearing were studied in a population of 109 chinchillas exposed to 1, 10, or 100 impulses presented at 150-, 155-, or 160-dB peak SPL at rates of one every 6, 60, or 600 s. The TTS and PTS were measured using the auditory evoked potential. Histological measures were obtained using standard surface preparation techniques. The following preliminary conclusions can be made. (1) There was no statistical difference in the amount of hearing loss or the amount of sensory cell loss for exposure to a single impulse at 150 or 155 or 160 dB peak SPL. Individual animals showed no permanent hearing loss and no significant sensory cell loss. (2) There was a considerable amount of variability or degree of susceptibility across animals as the severity of the exposure increased. This increase in susceptibility seemed to be tied more to peak levels of the stimulus than to the total energy. The variability produces, in extreme cases, a complete dichotomy in the results. (3) The permanent effects seemed to be dependent upon peak levels more than upon the total energy in the exposure stimulus. Also, for a constant peak and energy level, the more rapid presentation rate produced the greatest effect.