Hearing shift and inner ear pathology of guinea pigs exposed to octave bands of noise centered at 63 Hz and 4 kHz.
Twenty-four guinea pigs with normal Preyer's reflex were exposed to the octave bands of noise centered at 63 Hz and 4 kHz, 110 dB SPL. The duration of exposure was 4 and 8 hours respectively. The permanent shift of the guinea pigs at the above two frequencies was at 4-8 kHz. As the duration of exposure were 4 hours, the threshold shift at 63 Hz was smaller than that at 4 kHz. But as the duration of exposure was 8 hours, the threshold shift at 63 Hz and 4 kHz was almost the same. No morphological change of the inner ear was observed in the guinea pigs exposed for 4 hours at the octave bands of noise centered at 63 Hz and 4 kHz, but ultrastructural abnormalities were noted. After the animals were exposed for 8 hours, morphological, ultrastructural changes in the inner ear were observed. The main pathologic changes were seen at the second turn of the cochlea. These changes in hearing physiology and pathology suggest that a high intensive low frequency noise can result in high frequency hearing loss and that the use of A-weighted levels of specific damage risk criteria for noise sources may be inappropriate.
Department of Otorhinolaryngology, PLA Navy General Hospital, Beijing.
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Wang
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Jiang
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Qian
D000818:Animals; D001305:Auditory Fatigue; D001309:Auditory Threshold; D007758:Ear, Inner / Q000648:ultrastructure*; D006168:Guinea Pigs; D006199:Hair Cells, Auditory, Inner / Q000648:ultrastructure; D018072:Hair Cells, Auditory, Outer / Q000648:ultrastructure; D006317:Hearing Loss, Noise-Induced / Q000473:pathology*; D008854:Microscopy, Electron