Frequency weighted laser Doppler perfusion measurements in skin

The laser Doppler (LD) technique has been applied to measurements of blood perfusion in a number of studies and is the most popular method for investigating microcirculation in patients. The skin is supplied with nutrients by the capillaries, the smallest blood vessels. The nutritive blood flow within the capillaries is very slow and should be distinguished from the blood flow of other vessels such as those in deeper layers of the skin. In this work, a novel laser Doppler flux meter was used. In contrast to the usual LD technique that only provides a mean flux value, partial flux values can be calculated which are correlated to different flow velocities by analyzing different Doppler frequencies. The influence of the changes in the microcirculation on the spectral LD signal was investigated on the inner part of the wrist to select frequency bands, which would allow the best discrimination of capillary blood flux. The LD measurements were performed during selective compression of the skin. Results were obtained from different volunteers and the Doppler signal intensity in a frequency range from 50 Hz to about 400 Hz was found to correlate best with the capillary blood flux of the skin.