Laser Doppler imaging of skin microcirculation

Laser Doppler imaging (LDI), a new technique which allows measurement of skin blood perfusion at a distance from the skin surface, was assessed methodologically in healthy volunteers. Each skin LDI value was based on virtually real-time measurements obtained from a number of discrete measuring sites. In scans made along the circumference of the lower arm, valid figures for LDI (as distinct from no output at all) were obtained in 8/8 measurements at 0 degrees inclination, and in 16/16 measurements at 7 degrees, 14 degrees, 22 degrees, 30 degrees and 38 degrees, respectively. Beyond this inclination a numerical output was obtained in only 9/16 of measurements at an inclination of 48 degrees, in 7/16 at 69 degrees, and in no more than 1/16 at 90 degrees. Values obtained at angles of inclination greater than 38 degrees fell within the relatively narrow range of values obtained at lesser angles of inclination. The findings are of interest since measuring sites of clinical importance may not be flat. Variability of measurement (coefficient of variation in per cent) was studied in the lower leg by performing LDI and conventional laser Doppler flowmetry (LDF) concomitantly. The coefficient of variation for measurements in one subject at rest was 13% for LDI vs. 19% for LDF, the corresponding interindividual coefficient of variation values being 25% vs. 28%. In response to heating, finger pulp perfusion increased by 55% as measured by LDI (p = 0.0051) and by 44% (p = 0.0756) as measured by LDF. In summary, the findings contribute to the validation of LDI for skin perfusion measurement.