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Cochlear distribution of small focal lesions following exposure to a 4-kHz or a 0.5-kHz OBN.

Harding-GW; Bohne-BA
Abstr 29th Midwinter Res Meet 2006 Feb; 29:10-11
An octave band of noise (OBN) delivers fairly uniform energy over a specific range of frequencies (3-6 kHz for 4-kHz OBN & 0.375-0.750 kHz for 0.5-kHz OBN). Above & below these ranges, energy is at least 50 dB less than that in the OBN. Hair-cell loss often occurs outside the exposure OBN. The frequency location of hair-cell loss is evident when the % location of small focal lesions is analyzed. Data sets were assembled from our permanent collection of noise-exposed chinchillas using the following criteria: 1) The sum of exposure duration & recovery time was less than or equal to 10 days; 2) The exposure level was less than or equal to 108 dB SPL; & 3) Focal lesions were less than 1.5 mm in size. The data sets included a variety of exposures ranging from those that were high-level, short duration to those that were moderate-level, moderate duration. The % location of the center of each focal lesion was determined. Means, SDs & medians were calculated for lesion size for each OBN. Histograms were then constructed from the % location data using 2.0% bins & the counts were graphed relative to total number of lesions. For the 4-kHz OBN, 94% of the lesions were in the basal half of the OC & 6% were in the apical half. For the 0.5-kHz OBN, 29% of the lesions were in the apical half of the OC & 71% were in the basal half. The mean lesion size was 1.48% & 0.68% for the 4-kHz & 0.5-kHz OBN, respectively, with medians of 1.10% & 0.50%. The mean lesion size (in mm) for the 0.5-kHz OBN was less than half that for the 4-kHz OBN. For the 4-kHz OBN, a histogram of the % location of lesions showed that most occurred in the 5-7-kHz region, at & just above the upper edge of the OBN. Clusters of lesions were also found around 8 & 12 kHz. A cluster was present at & just below the lower edge of the OBN, as well as in the 1.5-kHz region. For the 0.5-kHz OBN, a histogram of the % location of lesions showed clusters at 0.25, 0.75 & 1.5 kHz in the apical half. In the basal half, the pattern was very similar (Pearson's r=0.69) to that seen with the 4-kHz OBN. The distribution of basal-turn lesions suggests that the 4-kHz & 0.5-kHz OBN are damaging that region of the cochlea in the same way.
Noise-exposure; Exposure-levels; Noise-induced-hearing-loss; Noise-exposure; Noise; Hearing; Hearing-disorders; Hearing-loss; Laboratory-animals; Animals;
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Abstracts of the 29th Midwinter Research Meeting
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Washington University, St. Louis