CHANGES IN DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS AND OUTER HAIR-CELLS FOLLOWING INTERRUPTED NOISE EXPOSURES

Changes in distortion product otoacoustic emissions (DPOAEs) were exam ined during and after interrupted noise exposures and compared to the condition of the outer hair cells (OHCs) and inner hair cells (IHCs) a s assessed by scanning electron microscopy (SEM). Binaural, adult chin chillas were exposed to a 95 dB SPL, octave band noise centered at 0.5 kHz for 15 days using a 3 h on/9 h off schedule. DPOAEs were measured before, during and after the exposures. DPOAE amplitudes decreased si gnificantly during the first few days of the interrupted noise exposur es and then began to recover. At most frequencies, the emission amplit udes recovered completely to pre-exposure baseline values by five days after the last exposure. The results of the present study indicate th at the changes in DPOAE amplitude paralleled the recovery in the ampli tude and threshold of the compound action potentials as reported previ ously (Boettcher et al., 1992). Although the DPOAEs completely recover ed, considerable OHC loss and stereocilia disarray was evident even fo ur weeks after exposure.