CAP amplitude after impulse noise exposure in guinea pigs.

In this study, 21 guinea pigs were submitted to a single high energy impulse noise (gun shot with blank projectiles). The auditory function was evaluated over a 7-day recovery period by recording the compound action potential (CAP) from the round window. The threshold shift and input/output function (CAP amplitude and delay function of the stimulus intensity) were studied at different frequencies. CAP amplitude fell after the noise trauma, especially at the lower sound level, resulting in a threshold shift. Latency was significantly increased. During recovery, whereas latency returned to its initial value, CAP amplitude gradually increased and, in half the animals, exceeded the control value for the higher levels of stimulus. This could have been because of progressive disinhibition or recruitment, and may correspond clinically to hyperacusis. These results are discussed referring to those obtained by other authors using other methods.