Fibre optic laser doppler velocimeter for medical applications

We describe a novel all-fibre optic laser Doppler velocimeter (FOLDV) which utilizes a low power stabilized single-mode laser and an optical fibre tap. After fundamental experiments to correlate the FOLDV signal to electromagnetic flowmeter (EMF) output, in vivo measurements of erythrocyte velocities have been made in both femoral and coronary veins and arteries. In experiments in which coronary blood flow was changed by electrical stimulators of sympathetic nerves, the FOLDV was able to measure velocity before, during and after the intervention where EMF failed to provide velocity information during intervention. In addition, the pulse wave velocities in femoral arteries were determined by referencing the FOLDV signal to vascular pressure. The FOLDV was also used to measure velocity profiles and vessel dimensions.