Abstract:
Cubic distortion product emissions (3DPE) were measured in four groups of chinchillas (N=4 or 5/group) exposed for 5 days, 24 h/d, to 121-dB peak SPL, narrow-band (400 Hz) impacts having center frequencies (CF) of 1.0, 2.0, 4.0, or 8.0 kHz. The noise exposure produced an asymptotic threshold shift (ATS) at audiometric test frequencies showing a threshold shift (TS). Levels of ATS up to 80 dB were measured at and above the CF of the impact. Surprisingly, the 1.0- and 2.0-kHz CF impacts produced the largest ATS at 16 kHz. There was, in general, a congruence between the ATS and 3DPE changes following exposures to CFs (greater than or equal to)2.0 kHz. However, with the 1.0-kHz CF impact exposure, the two metrics were not in general agreement. Relations among permanent thresholds shifts (PTS), 3DPEs and outer hair cell (OHC) losses were quite variable for low- and mid-frequency ((less than or equal to)2.0 kHz) biased lesions. For the 4.0- and 8.0-kHz CF impacts, 3DPE changes reflected OHC losses and PTS rather closely. DPEgrams using primary levels of 40 through 70 dB SPL in 10-dB increments were found to be most effective in the evaluation of OHC lesions than was any single DPEgram. [Research supported by NIOSH Grant No. R01 OH02317.]