EFFECTS OF SYMPATHECTOMY ON SKIN AND MUSCLE MICROCIRCULATION DURING DORSAL COLUMN STIMULATION - ANIMAL STUDIES

Electric stimulation of the dorsal spinal cord (DCS) in the treatment of pain in peripheral vascular disease is known to enhance peripheral circulation, but the mechanisms are still obscure. An earlier study has provided indirect evidence that the vasodilator effect is dependent upon alteration of sympathetic vasomotor activity. In the present study, surgical interruption of sympathetic pathways was performed to define the role of the sympathetic system for the stimulation-induced vasodilation. Three groups of normal rats were used: one group subjected to lumbar sympathectomy, one group sham-operated about 1 week before performing spinal cord stimulation, and a third group, without pretreatment, serving as a second control. Stimulation was applied to one dorsal column at the thoracolumbar junction, and peripheral microcirculation was recorded in hind limb skin and muscle by laser Doppler technique. The stimulation parameters were chosen to correspond with those used clinically in man. A cold test with monitoring of cold-induced changes in peripheral blood flow was used to assess the completeness of the sympathectomy. The preoperative cold test induced a reciprocal response, vasoconstriction in the skin and vasodilation in muscle. DCS with clinical parameters did not produce this reciprocity in the control and sham-operated rats, but induced a vasodilation in both skin and muscle. After complete sympathectomy, defined as postoperative disappearance of the vasomotor responses to cold, the vasodilation in skin and muscle in response to DCS was abolished; however, the vasodilatory response to high-intensity stimulation (approximately 10 times the motor threshold) was not affected. Incomplete sympathetic denervation in some animals resulted in partial preservation of a vasodilatory response to DCS. The results indicate a major contribution of the sympathetic system to DCS-induced peripheral vasodilation and explains why the method can be clinically effective also after chemical or surgical sympathectomy. It is likely that sympathetic vasoconstrictor activity is depressed by stimulation-induced activation of spinal inhibitory mechanisms, and that this constitutes a major component of the vasodilatory effect of DCS.