Direct evidence of neurally mediated vasodilatation in hairy skin of the human foot.

Abstract

SUMMARY1. Intraneural stimulation (i.n.s.) was made in the superficial peroneal nerve at the ankle in seventeen healthy subjects. The effect on skin blood flow was monitored by laser-doppler flowmeters and photo-electrical pulse plethysmographs inside and outside the innervation zone of the stimulated nerve fascicle. I.n.s. was applied before and after proximal local anaesthesia of the stimulated nerve.2. Painful i.n.s. (stimulation strength 0-3-4 V) induced skin vasodilatation with the following characteristics: (a) it occurred on the dorsal side of both feet, (b) the blood flow increase on the opposite foot was blocked by local anaesthesia of the nerve supplying the skin area under study, (c) the blood flow increase on the stimulated foot was abolished by proximal local anaesthesia of the stimulated nerve. The findings show that the vasodilatation was due to activation of a reflex pathway.3. The reflex vasodilatation was bigger in the stimulated than in the opposite foot. At the same time there were signs of skin vasoconstriction in the fingers. The reflex vasodilatation in the foot was enhanced by body cooling. It was unaffected by atropine or propranolol.4. After local anaesthesia of the nerve proximal to the stimulation site, i.n.s. with 2-6 times increased stimulation strength produced skin vasodilatation restricted to the innervation zone of the stimulated nerve fascicle. This response had greater amplitude and longer duration than the reflex vasodilatation.5. Intravenously administered atropine and propranolol did not affect the local dilatation to i.n.s. but after chronic treatment of the skin with capsaicin (1 % in ethanol), i.n.s. after a proximal nerve block induced skin vasoconstriction. In five of seven experiments subcutaneous injection of terbutaline (0'25 mg) in the innervation zone abolished the local dilatation.6. It is suggested that (a) the reflex vasodilatation is of sympathetic nature and is induced by stimulation of thin (Ad?) afferent fibres, (b) the local vasodilatation is due to centrifugally conducted impulses in (afferent?) non-myelinated fibres.

Skin blood flow disturbances in the contralateral limb in a peripheral mononeuropathy in the rat

“…This indicates that this response results from an increased level of afferent input from the loosely ligated sciatic nerve to the spinal cord. This finding agrees with the results of Blumberg and Wallin, 6 who also demonstrated that local anesthesia of a nerve proximal to its stimulation site completely interrupted the contralateral vasodilator response. Our findings also indicate that not only electrical, 6,32 but also other forms of excitation of nociceptive afferents (such as loose sciatic nerve ligation) may induce a vasodilator response in the contralateral extremity.…”

“…Blumberg and Wallin 6 have demonstrated that, in humans, painful intraneural electrical stimulation increases skin blood flow (SBF) not only ipsilaterally, but also in the contralateral extremity. Since the vasodilator response in the non-stimulated extremity occurred only when stimulation strength was high enough to cause sharp and localized pain, the authors proposed that the afferent limb of this reflex involves excitation of A-fibers.…”

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

“…With increasing currents the flow sometimes decreased linearly (Fig. 6) (Blumberg & Wallin, 1987). Sympathetic outflow to the foot reaches the sympathetic chain through preganglionic fibres in the T9-L2 ventral roots (Normell, 1974).…”

Immersing the foot in painfully-cold water evokes ipsilateral extracranial vasodilatation

“…Together, these findings suggest that noxious stimulation of the upper limb evokes vasoconstriction in that limb, possibly due to a nociceptive-sympathetic vasoconstrictor spinal reflex. Painful intraneural stimulation of the superficial peroneal nerve evokes vasoconstriction in the palm of the hand (Blumberg & Wallin, 1987). Surprisingly, however, this stimulus also elicits reflex vasodilatation in both feet which is greater on the stimulated than opposite side (Blumberg & Wallin, 1987) (Drummond & Granston, 2003;Drummond & Granston, 2004;Drummond, 2006a) could be organized either at the spinal level or more rostrally.…”

“…Painful intraneural stimulation of the superficial peroneal nerve evokes vasoconstriction in the palm of the hand (Blumberg & Wallin, 1987). Surprisingly, however, this stimulus also elicits reflex vasodilatation in both feet which is greater on the stimulated than opposite side (Blumberg & Wallin, 1987) (Drummond & Granston, 2003;Drummond & Granston, 2004;Drummond, 2006a) could be organized either at the spinal level or more rostrally. To distinguish between these two possibilities in the present study, we determined whether noxious stimulation of the lower limb (which is innervated by lumbar and sacral afferents and thus does not directly cross paths with sympathetic outflow to the face) would also evoke signs of ipsilateral extracranial vasodilatation.…”