Distance between laser head and skin does not influence skin blood flow values recorded by laser speckle imaging

BackgroundLaser Speckle contrast imaging (LSCI) allows non-contact, real-time recording of cutaneous blood flow (CBF). Different distances from laser-head to skin (distancesL–S) can be chosen by the operator to perform these recordings. We aimed to evaluate the impact of different DistancesL–S on the analysis of rest blood flow and post-occlusive reactive hyperemia (PORH). Methods Four distancesL–S (10, 15, 20, and 30 cm) were evaluated in a random order in 11 healthy subjects. We analyzed the concordance between each recording at each distanceL–S. We compared CBF results (absolute values and cutaneous vascular conductance (CBF divided by mean arterial pressure)) obtained for each distanceL–S. The intra-subject coefficients of variation due to distancesL–S (intra-CV, in%) were also studied. Results The mean “r” (standard deviation) cross-correlation coefficient was 0.99 (0.00) between each CBF trace issued from different distanceL–S. Both kinds of CBF results, at rest and for PORH peak, show non-significant differences when the distanceL–S is modified. The intra-CV varies from 5.9% to 8.6% at rest and from 5.6% to 9.1% for the PORH peak. Conclusion DistanceL–S neither influences SBFR at rest, nor at peak post-occlusive hyperemia in the 10–30 cm interval using LSCI