Influence of vibration on asymptotic threshold shift produced by impulse noise.

Monaural chinchillas were exposed for 10 days to one of these conditions: (1) whole-body vibration (30 Hz, 1 g rms acceleration); (2) impact noise (113 dB peak SPL 1/s) or (3) a combination of whole-body vibration and impact noise. Thresholds were monitored before, during and after the exposure using the auditory-evoked response or behavioral conditioning techniques. Vibration alone had essentially no effect on threshold. Exposure to impact noise produced a stable asymptotic level of threshold shift 2-8 h after exposure onset. The asymptotic threshold shift was roughly 35 and 43 dB SPL at 0.5 and 8.0 kHz, respectively. Exposure to impact noise plus vibration produced an asymptotic threshold shift at 0.5 and 8.0 kHz that was approximately 10 dB greater than noise alone. The combination group also showed greater permanent threshold shifts and greater hair cell losses than the group exposed only to impact noise. The results imply that impact noise and whole-body vibration, at levels commonly found in industrial settings, can interact to increase the susceptibility of the chinchilla cochlea to noise-induced hearing loss.