Laser Doppler measurements of skin vasodilation elicited by percutaneous electrical stimulation of nociceptors in humans.

This study was designed to assess the quantitative features of the skin protecting mechanism of axon reflexes by monitoring stimulus related changes in skin blood flow using laser Doppler flowmetry. Skin vasodilatation induced by trains of brief transcutaneous electrical pulses (0.5 ms, 150 V) was strictly related in magnitude to the number of pulses (trains of 1-32). This vascular response was reduced by 95% when the skin had been pretreated by painting it for two days with a 1% alcoholic solution of capsaicin. The sensitivity of vascular responses to activation of afferent C-fibers indicates a role of this mechanism in the protection of the skin against noxious events.