Effect of burst-mode transcutaneous electrical nerve stimulation on peripheral vascular resistance

Background and Purpose. Based on changes in skin temperature alone, some au thors have proposed that postganglionic sympathetic vasoconstrictor fibers can be stimulated transcutaneously. Our goal was to determine the effects o f low-frequency (2 bursts per second), burst-mode transcutaneous electrical nerve stimulation (TENS) on calf vascular resistance, a more direct marker of sympathetic vasoconstrictor outflow than skin temperature, in subjects with no known pathology. Subjects. Fourteen women and 6 men (mean age = 31 years, SD = 13, range = 18-58) participated in this study. Methods. Calf bl ood flow, arterial pressure, and skin temperature were measured while TENS was applied over the common peroneal and tibial nerves. Results. Blood flow immediately following stimulation was not affected by TENS applied just un der or just above the threshold for muscle contraction. Transcutaneous elec trical nerve stimulation applied at 25% above the motor threshold caused a transient increase in calf blood flow. Regardless of stimulation intensity, TENS had no effect on arterial pressure; therefore, calf vascular resistan ce decreased only during the trial that was 25% above the motor threshold. Regardless of stimulation intensity, TENS failed to alter dorsal or plantar skin temperature. Discussion and Conclusion. These results demonstrate tha t the effects of TENS on circulation depend on stimulation intensity. When the intensity was sufficient to cause a moderate muscle contraction, a tran sient, local increase in blood flow occurred. Cooling of the dorsal and pla ntar skin occurred in both the stimulated and control legs, most likely bec ause skin temperature acclimatized to ambient room temperature, rather than because of any effect of TENS on circulation. The data, therefore, call in to question the idea that postganglionic sympathetic efferent fibers are st imulated when TENS is applied at clinically relevant intensities to people without symptoms of cardiovascular or neuromuscular pathology.