The effect of sympathetic blockade on facial sweating and cutaneous vascular responses to painful stimulation of the eye.

The vascular response in the forehead to stimulating the eye with soapy water was investigated in 15 subjects shortly after pharmacological blockade of the stellate ganglion. Electrodermal activity was also recorded from each side of the forehead in nine subjects. Pulse amplitude and electrodermal activity increased on the stimulated side of the forehead. Sympathetic blockade had no consistent effect on the vascular response, which was similar in magnitude on the blocked and sympathetically intact sides. In contrast, the electrodermal response was greater on the blocked side of the forehead, suggesting that sympathetic blockade had removed an inhibitory influence. The findings demonstrate that cervical sympathetic outflow does not increase vasodilatation or local sweating in the forehead during painful stimulation of the eye. Conjunctival irritation induces a trigeminal-parasympathetic vasodilator reflex in the forehead circulation. Release of vasoactive intestinal polypeptide from parasympathetic terminals during this reflex might increase local sweating.