Changes in distortion product otoacoustic emissions (DPO) and cochlear microphonics (CM) induced by impulse noise exposure in Guinea Pigs

Distortion product otoacoustic emissions (DPO) and cochlear microphonics (CM) were recorded before and 1, 48 hours, and 1 week after impulse noise exposure in guinea pigs. The results showed that before noise exposure, the adequate frequency ratios (f₂/f₁) and adequate intensity difference (I_f1-I_f2) were between 1.19-1.25 and 0.45-2.00 dB, respectively. The incidence of appearance of DPO was 100% at 8 and 4 kHz, 95% at 2 kHz and 79% at 1 kHz. After noise exposure, the changes and recovery rate of DPO differed from those of CM in all periods. In particular, changes in DPO were greater than those of CM. DPO at all frequencies recovered only to about 1/4 of the pre-exposure level, with the only exception that recovery was complete after 1 week at 8 kHz. In contrast, CM at all frequencies recovered to the pre-exposure level at the same time. The results seem to indicate that DPO is more sensitive to noise exposure than CM and, also, that the former changes proir to CM. Correlation analysis between DPO and CM suggests that both originate from the outer hair cells (OHC).