SYMPATHETIC-NERVE ACTIVITY AFTER ACUPUNCTURE IN HUMANS

The aim of the present study was to determine if acupuncture stimulati on inhibits sympathetic nerve activity in humans. Multiunit efferent p ostganglionic sympathetic activity was recorded with a tungsten microe lectrode inserted in a muscle fascicle of the peroneal nerve. Mean art erial pressure, heart rate and skin blood flow were also monitored. Pa in thresholds were measured by electrical tooth pain stimulation. Afte r a 30 min rest, acupuncture needles were inserted bilaterally into th e Li 11 and the Li 4 acupuncture points, and manipulated until 'chi' c ramp-like sensation was reported. Electrical stimulation (2 Hz, 0.6-0. 8 ms duration, maximal tolerated stimulation without discomfort) was d elivered for 30 min and the physiological recordings were continued fo r 90 min after the end of acupuncture. In a placebo control experiment , the same procedure was followed, except that acupuncture needles wer e inserted subcutaneously and no manipulation or stimulation was given . The stimulator delivered pulses to an unconnected channel, hence, th e same audiovisual stimuli were experienced as with acupuncture, and c are was taken to ask the same questions about sensations in the placeb o and the acupuncture groups. Electroacupuncture produced an increase in pain threshold which was paralleled by a transient increase in musc le sympathetic nerve activity. During acupuncture, there was a small i ncrease in heart rate and mean arterial pressure, but there was no pos t-acupuncture hypotension. The placebo control procedure did not chang e pain threshold or sympathetic nerve traffic. The findings suggest th at electroacupuncture produces moderate hypoalgesia in humans parallel ed by a significant increase in muscle sympathetic nerve activity. (C) 1998 International Association for the Study of Pain. Published by El sevier Science B.V.