NEUROGENIC FLARE RESPONSES ARE HETEROGENEOUS IN SUPERFICIAL AND DEEP LAYERS OF HUMAN SKIN

Infrared thermography and video image analysis were used to compare the development of the neurogenic flare response in deep and superficial skin layers. Neurogenic vasodilatation was induced by injection or iontophoretic application of histamine. Thermograms were recorded every 10 s to evaluate the local warming reaction. Color-video image analysis was used for computerized delineation of the visible flare. Images derived from video analysis were superimposed to the thermograms after linear transformation. The thermal reaction started within 10 s simultaneously at 2-5 distinct spots after histamine application at distances of 4-25 mm from the application site while the flare reaction seemed to spread from the application site when it became visible after a delay often exceeding 20 s. The visible flare but not the warming reaction was suppressed by topically applied local anesthetic (EMLA(R)). Warming at focal spots was also observed during post-occlusive hyperemia. About 70% of these spots were identical to those activated by histamine. The results indicate that the vascular axon reflex is differently organized in different layers of the skin.