Correlations among evoked potential thresholds, distortion product otoacoustic emissions and hair cell loss following various noise exposures in the chinchilla

Changes in cubic distortion product otoacoustic emissions (Delta DPOAEs), evoked potential threshold shifts (TSs) and outer hair cell (OHC) losses were measured in a population of 95 noise-exposed chinchillas. Each animal was exposed to one of 23 different noises in an asymptotic threshold shift (ATS) producing paradigm or an interrupted noise paradigm which typically produced a toughening effect. Noises were narrow band (400 Hz) impacts with center frequencies of 0.5, 1.0, 2.0, 4.0 or 8.0 kHz presented 1 impact/s at peak SPLs of 109, 115, 121 or 127 dB. The duration of the exposures was 24 h/day for 5 days (ATS paradigm) or 6 h/day for 20 days (toughening paradigm). Based on a linear regression analysis of individual subject and group mean data, correlations among the following dependent variables were made: Delta DPOAEs, ATS: toughening or TS recovery (TSr), permanent threshold shift (PTS) and OHC loss. Correlations among these metrics were generally highest for DPOAE primary frequency levels, L-1 = L-2 = 70 dB. Correlation between Delta DPOAE and TSr was typically low, while a considerably higher correlation was found between Delta DPOAE and ATS. Correlations among the permanent measures of noise-induced effects, i.e. for Delta DPOAE/PTS and Delta DPOAE/OHC loss were typically poor when there was only a small or a moderate noise-induced effect (PTS < 25 dB and <Delta>DPOAE < 20 dB). However; for PTS < 25 dB the correlation between PTS and OHC loss was considerably better than the correlation between Delta DPOAE and OHC loss. For more severe noise-induced changes there was generally a good correspondence between OHC loss, PTS and Delta DPOAE metrics. (C) 2000 Elsevier Science B.V. All rights reserved.