[The influence of infrasound vibration upon cochlea]

White guinea pigs were exposed to sound (White noise, 100 dB. SPL. or 4 kHz. pure tone 115 dB. SPL. 2 hours) and infrasound (Frequency 10 Hz. amplitude 5mm, 4 or 6 hours), independently or simultaneously to study the influence of infrasound vibration upon the cochlea. After the exposure, amplitude and latency time of the AP of the electrocochleogram was studied by inserting a needle into the cochlea under intraperitoneal anesthesia. The electrocochleogram was obtained by averaging response to 256 clicks at a rate of 8 per second. The results showed that the amplitude of the AP significantly decreased when guinea pigs were exposed to both 4 kHz. pure tone and infrasound vibration with 10 Hz., and 15 Hz. (P less than or equal to 0.05). The latency time of the AP was slightly prolonged, when they were exposed to infrasound with 15 Hz. A few cochlea showed histopathologically a collapse of Reissner's membrane. As the next experiment, the guinea pigs were exposed to infrasound (20 Hz., 115 dB. SPL) from loudspeaker 3 hours in free field. Auditory brain stem response (ABR) was performed before and after the exposure. The amplitude and latency time of P1 in ABR showed no remarkable difference after the exposure. These results imply that the exposure to sound and infrasound vibration have an effect upon the physiological function of the guinea pig.