Laser Doppler perfusion monitoring of skin blood flow at different depths in finger and arm upon local heating.

The purpose of the study was to elucidate the vasodilatory response to local heating of the skin at two depths in two locations. To accomplish this, we measured skin blood flow in 12 healthy subjects using laser Doppler perfusion monitoring. A probe with two fibers separated 0.14 mm (superficial) and 0.25 mm (deeper) from the illuminating fiber was first attached to the distal phalanx of the index finger and thereafter to the dorsal forearm skin. Local heating was caused with a thermostatic probe holder set at 40 degrees C. We studied the perfusion value and its two components, velocity and concentration. All registrations were also subjected to frequency analysis. Laser Doppler values were generally higher in the fingertip than in forearm skin. Heating caused increased values at both locations. Concentration increased relatively more than velocity and this was most obvious in the forearm. There were only slight differences in response between superficial and deeper vascular components. Frequency analysis revealed a peak in perfusion and velocity obviously related to the heartbeat. Movement of the column of blood thus reached the peripheral vascular network without changing concentration. We conclude that local heating increases skin blood flow in fingertip and forearm skin by different adjustments of blood cell concentration and velocity, presumably depending on differing vascular anatomy and physiological control, but differences are of a rather minor character. Furthermore, responses differ just slightly in superficial compartments as probed with fibers separated up to 0.25 mm.