Effects of frequency and intensity of sound on cochlear blood flow

Laser Doppler flowmetry demonstrates that loud sound induces a decrease of blood flow in the cochlea of the guinea pig. In this experiment, we observed the effects of frequency and intensity of sound on cochlear blood flow using 15 guinea pigs. In the first 5 guinea pigs, a Doppler probe was attached to the basal turn of the cochlea and sounds of 6, 7, 8, 9 and 10 kHz were delivered to the ear serially from lower to higher frequency, i.e. from 6 kHz to 10 kHz. In the next 5 guinea pigs, the sound was delivered from higher to lower frequency, i.e. from 10 kHz to 6 kHz. The sound intensity delivered to the ear was changed from lower to higher intensity (80 to 120 dB SPL by 10 dB width) at each frequency. In the last 5 guinea pigs, the blood flow in the basal, second, third, and fourth turns of the cochlea was measured at 120 dB SPL of 10 kHz. No change of blood flow was seen in the cochlear basal turn at 6 and 7 kHz up to 120 dB SPL, but a decrease of blood flow was found at 110 and 120 dB SPL at 8, 9, and 10 kHz. On the other hand, the sound of 120 dB SPL at 10 kHz induced a decrease of blood flow only in the basal turn of the cochlea. Our results suggest that there is a corresponding blood flow area which is sensitive to specific frequency in the cochlea.