OBSERVATIONS OF A LASER DOPPLER FLOWMETER OUTPUT MADE USING A CALIBRATION STANDARD

Laser Doppler flowmetry (LDF) is a noninvasive method of continuously determining tissue perfusion. It uses the principle that laser light backscattered from tissue is spectrally broadened by Doppler shifts produced by moving red blood cells (Stern, 1975). Optical heterodyning in a suitable detector is used to detect the shifts. Until recently, there has been no standard against which any LDF could be calibrated. A standard has now become available (Periflux Motility Standard) which consists of a solution of particles undergoing Brownian motion which produce a known, constant output allowing all instruments to be set to this value, when the probe is immersed in it. Measurements made with machines calibrated in this way should be directly comparable. This communication reports some problems revealed during the use of this standard. 12 Refs.