The relationship among distortion-product otoacoustic emissions, evoked potential thresholds, and outer hair cells following interrupted noise exposures.

Distortion-product otoacoustic emissions (DPOAEs) are gaining popularity as indicators of the status of the cochlea. The efficacy of DPOAEs as indicators of changes in thresholds and the status of outer hair cells (OHCs) were examined using an animal model. Monaural chinchillas were exposed to an octave band noise (OBN) centered at 0.5 kHz at 95 dB SPL for 6 hr/day for 10 days. DPOAEs and evoked potential thresholds were recorded before, during, and after the exposures. The animals were sacrificed 5 days after the last exposure, and the status of OHCs was assessed using scanning electron microscopy. Results indicate that both evoked potential thresholds and DPOAEs effectively track the temporary changes associated with interrupted noise exposures. However, DPOAEs often recovered to their baseline even when there was a threshold shift of > 25 dB. Furthermore, at 5 days postexposure, both evoked potential thresholds and DPOAEs were normal despite considerable OHC pathology. The findings suggest that normal DPOAEs may not guarantee normal cochlear status and, therefore, results of DPOAE measurements should be interpreted cautiously.