[Interaction between continuous and impulse noise: anatomic and functional evaluation in relation to the intensity of the exposure].

Interaction between continuous and impulse noise was studied. One group of chinchillas was exposed to octave band of noise of 0.5 kHz 95 dB SPL intensity. Three groups were exposed to impulse noises of 113, 119 and 125 prak SPL emitted at 1 imp/sec, 1 imp/4 sec and 1 imp/16 sec respectively. Three groups were exposed to noise created by a combination of above continuous and impulse noises. All exposures lasted for 5 days. Hearing thresholds were measured in 35 animals using auditory evoked potentials. The combined continuous and impulse noises showed equal energy contents, but the groups exposed to 119 and 125 dB impulse noise intensities developed an exacerbation of PTS and cell hair loss. Therefore, the critical level, under which the damage associated with noise exposure is related to the total noise energy (Equal Energy Hypothesis) was reduced when impulse noise was added to continuous noise.