[Sympathetic skin response as an objective indicator of sympathetic activity]

Sympathetic excitement is not rarely accompanied by sweating over the palm or sole, and this sudatory reaction is often depressed by atropine. But, there was no simple way for quantitative expression of sympathetic activity. As an objective indicator of sympathetic activity, sympathetic skin response (SSR) was studied in 17 volunteers and 5 patients in the pain clinic. SSR was evoked by square wave electric stimulation through a pair of surface electrodes placed on the unilateral forearm. SSR recorded with a surface electrode was much larger than that was taken with a needle electrode inserted deep under the skin, and was markedly reduced by an intravenous administration of atropine sulfate 0.5mg for about 10 min. These findings support the hypothesis that the SSR is developed by an action potential of eccrine glands of a cholinergic nature. Unilateral stellate ganglion block abolished SSR in the ipsilateral palm indicating that the efferent impulse of palmal SSR is transmitted via cervical sympathetic ganglion. Inhalation of 0.1MAC halothane or enflurane in air reduced the height of SSR within 10 minutes. They obtunded SSR dose-dependently, and almost completely abolished at a concentration of 0.3 MAC. SSR may be useful to evaluate sympathetic activity under various conditions, such as under the effect of sedatives, analgesics and general anesthetics, and to evaluate the effects of a nerve block or other drugs which were used to obtund the nociceptive afferent stimuli to the sympathetic center of the brain.