Laser Doppler measurements of cochlear blood flow during loud sound presentation.

The laser Doppler flowmeter may give responses to loud sound that reflect the vibration of cochlear structures rather than changes in cochlear blood flow. The present study demonstrates that the positive artifactual response (i.e., increased flow reading) to sound at frequencies above approximately 5 kHz can be eliminated by using flowmeters which have electronic filters at 4 and 12 kHz, limiting the bandwidth of the optical Doppler shifted frequency range to lower frequencies. However, when using the 4 kHz filter a "residual" immediate negative response to loud high-frequency sound (10 kHz tone at 125 dB SPL) is evident at the beginning of the exposure. These findings are discussed with regard to the suitability of the method for investigating the effect of sound/noise on cochlear blood flow.