Velocity resolved laser Doppler blood flow measurements in skin

A Doppler flow meter was developed, consisting of a PC and a control card for two Doppler sensors to be fixed on skin. From the measured Doppler signals a power spectrum is calculated by a software FFT. In contrast to usual laser Doppler flow measurements in skin, which provide only a mean flow, a flow spectrum is calculated with the assumption of an isotropic distribution of the directions of the velocity of the erythrocytes and irradiation vectors in the skin. Up to four partial flows (integral over a certain frequency region of the flow spectrum) are displayed on the screen simultaneously with a resolution in time < 10 ms. The frequency span can be set independently for each few. Corresponding to low and high Doppler frequencies the flows show different behavior and provide the possibility to distinguish between the flow in the superficial dermal plexus and larger micro-capillaries. (C) 1997 Elsevier Science Ltd.