FACTORS AFFECTING THE APPEARANCE AND PERSISTENCE OF VISIBLE CUTANEOUS REACTIVE HYPEREMIA IN MAN 1

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Abstract
The factors affecting cutaneous reactive hyperemia in man were studied semi-quan-titatively by means of a previously described method in which blood flow in the skin was stopped locally by applying a weighted ring to the volar surface of the forearm. The end points used were (a) the duration of occlusion required to produce a clearly visible ring of hyperemia (threshold) and (b) the time required for skin color to return to normal (clearing time). Lowering of tissue temp. produced a moderate increase of threshold and clearing time between 37[degree] and 32[degree] C and very conspicuous increase of both between 32[degree] and 27[degree] C. Reasons are given for ascribing the former to the action of metabolites predominantly, and the latter to heightened vasconstrictor tone acting against the dilator effect of metabolites. Increasing venous pressure by congestion or by dependency of the forearm lowered threshold and increased clearing time. Elevation of the forearm or application of pressure to the surface of the forearm increased threshold but did not affect clearing time. It appears that these factors act by their mechanical effects on the sub-papillary venous plexus and consequently on the visibility of a given increase of arterial blood flow. Iontophoresis of epinephrine, by increasing the tone of the minute vessels, increased both threshold and clearing time conspicuously. If venous pressure and skin temp. are kept constant local reactive hyperemia can be used to detect rapid changes in the tone of the minute vessels of the skin in man.