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Comparison of noise-Induced DPOAE temporary level shift with detailed histopathology.
Harding GW; Bohne BA
Abstr Midwinter Res Meet Assoc Res Otolaryngol 2004 Feb; 27:132
DPOAE temporary level shift (TLS), ABR temporary threshold shift (TTS), and detailed histopathology were determined in 3 groups of chinchillas exposed to an octave band of noise (OBN) centered at 4 kHz at either 80, 86 or 92 dB SPL for 24 hours (n=3, 4, 6). DPOAEs at 39 frequencies from f1=0.3 to 16 kHz (f2/f1=1.23; L2 & L1=55, 65 & 75 dB, = & not equal) and ABR thresholds at 13 frequencies from 0.5 to 20 kHz were collected pre- and post-exposure. The functional data were converted to pre- minus post-exposure shift and overlaid upon the cytocochleogram of cochlear damage using the frequency-place map for the chinchilla. The magnitude and frequency-specific location of components in the 2f1-f2 TLS patterns were determined and group averages for each OBN and L1, L2 combination were calculated. The f2-f1 TLS was also examined in ears with focal lesions > 0.4 mm. The 2f1-f2 TLS (plotted at f1) and TTS aligned with the extent and location of damaged supporting cells. The TLS patterns had two features which were unexpected; a local minimum at about a half octave above the center of the OBN with a local maximum above and below it, and a local minimum (often with negative shift) at the apical boundary of the supporting-cell damage. The magnitudes of the TLS and TTS generally increased with increasing exposure SPL. The peaks of the TLS and TTS, as well as the local TLS pattern components moved apically as the OBN was increased. However, there was no consistent pattern-relation with L1, L2 combinations. In addition, neither the 2f1-f2 nor f2-f1 TLS for any L1, L2 combination consistently detected focal lesions (100% OHC loss) from 0.4 to 1.2 mm in length. Often at focal lesions, the TLS went in the opposite direction from what would be expected. Thus, TLS is sensitive to and reflects a differing mechanism for noise-induced temporary hearing loss than for permanent hearing loss.
Noise-exposure; Exposure-levels; Noise-induced-hearing-loss; Noise-exposure; Noise; Hearing; Hearing-disorders; Hearing-loss; Laboratory-animals; Animals; Cell-damage; Cellular-reactions
Disease and Injury: Hearing Loss
Abstracts of the 27th Midwinter Research Meeting of the Association for Research in Otolaryngology, Febuary 21-26, 2004, Daytona Beach, Florida
FL; NJ; MO
Washington University, St. Louis
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