The interaction of whole body vibration and impulse noise.

Three groups of chinchillas, each consisting of five monaural animals, were exposed to one of three conditions: 1 h of sinusoidal, 30-Hz vibration at 1 g rms; 50 noise impulses at 155 dB, 1.5-m A duration, at the rate of 1/min; or a combination of the vibration and the impulse noise. Before exposure, and at various times after exposure, each animal's auditory evoked responses (AER) were measured at seven frequencies between 0.5 and 8.0 kHz. Thirty days after the exposure all animals were sacrificed for cochlear surface preparation histology. Chinchillas exposed to the vibration alone showed no significant temporary or permanent change in AER thresholds. The group exposed to impulse noise showed a maximum median TTS of from 34 dB at 0.5 kHz to 72 dB at 2 kHz and a flat PTS of 15-20 dB between 1 and 2.8 kHz. The combination group at all test times and frequencies showed a greater TTS and PTS than did the groups exposed to noise or vibration alone. The cochleograms are related in a variety of ways with hearing thresholds. The data from all three groups of experimental animals are consistent and demonstrate a potentiating effect of vibration on an impulse noise exposure.