Laser Doppler measurement of cochlear blood flow changes during conditioning noise exposure

Using laser Doppler flowmetry, cochlear blood flow was assessed in Mongolia n gerbils exposed to noise. Anesthetized animals were surgically implanted with permanent electrodes and then exposed for 10 consecutive days (6 h on/ 18 h off) to an octave band noise centered at 4 kHz (85 dB SPL). The audito ry brainstem responses and the blood flow in the basal turn of the cochlea were compared with those of gerbils not exposed to noise. The exposed anima ls developed an initial threshold shift, followed by a progressive reductio n in threshold shift up to complete recovery at the end of the test, In the exposed animals, a reduction in the cochlear blood flow during the first 4 days of exposure was observed, which was then followed by a progressive in crease up to the end of the test. The results of this study exclude a possi ble role of the microvasculature of the lateral cochlear wall in determinin g the resistance to 4 kHz frequency noise exposure.