Evaluation of cochlear blood flow measurement by laser Doppler flowmetry

The penetration depth of the cochlea was investigated by measuring the fluid flow in a physical model and by in vivo experiment. Blood flow under the dissected lateral bony wall of the cochlea was recorded for a fluid flow model consisting of a bundle of optical fibers surrounded by a strongly scattering medium. The measured laser Doppler signal was proportional to the product of red blood cell volume and mean velocity. In the in vivo study the output of a laser Doppler flowmeter was recorded directly from the lateral bony wall of cochlea and after covering it with the dissected dead bony wall. The changes of flow pattern following drug injection were similar in both of the outputs, but the magnitude of the output when a piece of dead bone was present averaged one fourth that of the original output. These results showed that the laser light penetrated through the lateral bony wall and reached the vascular area including the stria vascularis and superficial vessels