ARTERIOVENOUS ANASTOMOSES AND THE THERMOREGULATORY SHIFT BETWEEN CUTANEOUS VASOCONSTRICTOR AND VASODILATOR REFLEXES

The reflex changes in skin blood flow which occur in response to vario us non-thermal stimuli (e.g., deep inspiratory gasps, arousing or pain ful stimuli, emotional stress) are profoundly influenced by the thermo regulatory state. The aim of the present study was to evaluate the inv olvement of arteriovenous anastomoses in the thermoregulatory modulati on of skin vasomotor reflexes elicited by painful intraneural electric al stimulation and emotional stress (forced arithmetics), respectively . Vasomotor responses were recorded with laser Doppler flowmeters (LDF ) placed on glabrous skin containing arteriovenous anastomoses (3rd fi nger and thenar eminence) and hairy skin which lack them (dorsal side of the first metacarpal bone). In some experiments, a laser Doppler fl owmeter emitting laser light of two different wavelengths (infrared an d green light) into the same skin site was used to record skin perfusi on at different depths of glabrous skin on the thenar eminence. 40 sub jects were investigated, both in the cold state (finger skin temperatu res below 25 degrees C) and after subsequent warming (finger skin temp eratures above 30 degrees C). Thermoregulatory modulation of electrica l stimulation- or stress-induced vasomotor reflexes occurred both in g labrous and hairy skin, but hairy skin differed from glabrous skin by showing no significant vasoconstrictions. Relative perfusion changes w ere most marked in laser Doppler flowmeter recordings using the deeper penetrating infrared light. The results suggest that arteriovenous an astomoses are major contributors to the vasoconstrictor component of v asomotor reflexes in glabrous skin of warm subjects. The reflex increa se in perfusion, on the other hand, which occurs in both glabrous and hairy skin of cold subjects may-be mediated by resistance vessels.