Laser-Doppler methods for the assessment of microcirculatory blood flow

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Abstract
A new principle for the measurement of microcirculatory blood flow is described. The laser Doppler flowmeter u tilises the fact that a laser light beam incident on tissue is scattered in static structures as well as in moving red cells. Light beams scattered in moving red cells undergo a frequency shift according to the Doppler effect, while beams scattered in static tissue alone remain unshifted in frequency. If shifted and unshifted light is mixed on a photodetector surface, beat notes are produced. The power spectral density of these beat notes is determined by red cell concentration and velocity. From the alternating portion of the photocurrent, an output signal that is related to flux of red cells in a specific tissue volume can be calculated. Some applications of the method are presented.