Direct evidence of active sympathetic vasodilatation in the skin of the human foot.

1. During operative aorto-femoral vascular reconstructions on sixteen patients, the sympathetic chain was stimulated electrically between the L2 and L4 ganglia while blood flow was monitored by laser doppler flowmeters from the skin on the sole of the foot and the ankle and by an electromagnetic flowmeter from the deep femoral artery. Epidural anaesthesia to at least the T6 level was used which excluded reflex effects. 2. Stimulation (10 Hz) at 1-12 mA current strengths for 30 s evoked both reductions and increases of blood flow in glabrous and hairy skin. Initial short-lasting flow increases (durations 9-19 s) followed by sustained decreases were common: sometimes there were sustained flow increases at low and decreases at high current strengths. 3. In the deep femoral artery (supplying predominantly muscle) only flow reductions were evoked. 4. The results provide evidence for sympathetically mediated vasodilatation in the skin of the human foot whereas leg muscles may be supplied by vasoconstrictor nerves only.