[Threshold shift and inner ear pathology in guinea pigs exposed to octave bands of noise at 63 Hz and 4 kHz].

So far there have been few studies on the effect of low frequency noise on auditory organs. Twenty-four Preyer's reflex normal guinea pigs were exposed to the octave bands of noise at 63 Hz and 4 kHz, 110 dB A (SPL). The durations of exposure were 4 and 8 hr. It was discovered that the permanent threshold shift for both frequencies was at 4-8 kHz. In guinea pigs exposed 4 hrs, the threshold shift for 63 Hz was smaller than that for 4 kHz, while the threshold shift for 63 Hz in guinea pigs exposed 8 hr was similar to that of 4 kHz. No change in inner ear morphology was observed in guinea pigs exposed 4 hrs to the octave band of noise at 63 Hz and 4 kHz, but ultrastructural abnormality was demonstrated. When the animal was exposed 8 hr, changes in inner ear morphology and ultrastructure were seen. The main pathological changes were at the second coil of the cochlea. The auditory changes suggest that an intensive low frequency noise may induce a high frequency hearing loss. The result also indicates that using A-weighted level to determine the damage risk criteria of noise is inappropriate.