Interaction of sinusoidal vibration and impulse noise: Effects on hearing

Combinations of whole body vibration and impulse noise exposures can lead to a severe potentiating effect. Three groups, each consisting of five monaural chinchillas, were exposed to (1) 1‐h of sinusoidal, 30‐Hz vibration at 1 g rms, (2) 50 noise impulses at 155‐dB, 1‐msec A duration, at the rate of 1/min and (3) a combination of the above vibration and impulse noise. For each group of animals hearing thresholds were estimated before and after exposure at seven frequencies between 0.5 and 8 kHz using evoked response audiometry. Thirty days after the exposure all animals were sacrificed for cochlear histology. Chinchillas exposed to the vibration alone showed no temporary or permanent change of hearing threshold. The group exposed to impulse noise alone sustained a maximum median TTS from 35 dB at 0.5 kHz to 70 dB at 2 kHz. Losses at 30 days showed a maximum of approximately 20 dB at 1.4 kHz with little (<10 dB) or no loss at the other test frequencies. The combination group at all times and test frequencies showed a greater TTS (as much as 25 dB) and a PTS of from 20 to 33 dB at frequencies between 0.5 and 4 kHz. Cochleagrams will be presented with the detailed audiometric data. [Work partially supported by National Institute of Environmental Health Science, Grant NO. 2‐R01‐ES‐00969]