Spatial and temporal variations in human skin blood flow.

Microcirculatory human skin blood flow was studied with laser Doppler flowmetry. The recorded mean flow and its heart synchronous variations were shown in animal experiments to have their origin in moving red cells in the tissue under study. A low, steady and reproducible baseline not coinciding with zero output signal was, however, recorded in tissue with arrested blood flow. The methodological error determined as the coefficient of variation in repeated measurements of the Brownian mobility of a stable emulsion was estimated to be lower than 6%. From intraindividual recordings made on adjacent forearm skin areas with an apparently homogenous perfusion, significant (0.1%) spatial differences in blood flow were demonstrated. In skin blood flow recordings on forehead and forearm skin, made at 20-min intervals, slow fluctuations around the average value were found. Corresponding coefficients of variation were between 4 and 19%. The median coefficient of variation for repeated measurements at the same probe position during one hour was 25%. Wide day-to-day variations in skin blood flow were demonstrated on the forehead, forearm, fingertip and foot. Pronounced variations were also found in recordings made on bilateral and symmetrical skin regions. The results underline the importance of taking into account the natural spatial and temporal variations in dermal microvasculature when designing a stimuli-response experiment that includes the study of skin blood flow.