The effects of reverberant blast waves on the auditory system

Chinchillas were exposed to 1, 10, or 100 reverberant impulses at 150, 155, or 160 dB peak SPL. The impulses were generated by one of two different shock tubes, each producing blast waves having a different spectral composition, with one emphasizing low frequencies (< 0.5 kHz) and the other midfrequencies (2-4 kHz). Impulses were presented at the rate of one per minute. This parametric paradigm yielded 18 exposure conditions with 15 animals/condition. Hearing thresholds were measured using auditory-evoked potentials and the sensory epithelium was evaluated with the surface preparation. In general, trauma increased as the total energy of the exposure, determined by the peak SPL and number of presentations, increased. The dependent variables (permanent threshold shift and sensory cell loss) varied in an orderly fashion across frequency as the peak and number of presentations were increased for both blast wave sources. There were, however, consistent differences between the effects of the low- and high-frequency energy "content" blast waves. Correlations between the dependent variables and the energy of exposure were highest for P- or A-weighted energies [Patterson et al., J. Acoust. Soc. Am. 93, 2860-2869 (1993)].