The local sweat rate (LSR) response to intradermal electrical stimulation generates a sigmodal stimulus-response curve with a peak sweat rate generated during a 30 s period of continuous stimuli at a frequency of 16 to 32 Hz. However, the in vivo firing pattern of the sudomotor nerve resembles more of a bursting pattern. We tested the hypothesis that a bursting pattern during intradermal electrical stimulation would result in a greater sweating response than the regular continuous stimulus pattern. 15 subjects were studied in a temperature-controlled room at 27.6 ± 0.2 {degree sign}C. The LSR was measured with a miniature sweat capsule with guide sleeves for holding the intradermal stimulating electrodes. The nine continuous stimulus frequencies (0.2, 1, 2, 4, 8, 12, 16, 32, and 64 Hz) were compared to a bursting pattern with a similar total number of stimuli. The sweating response was determined as the area under the LSR-time curve. Peak LSR was slightly higher for the continuous stimuli (0.396 ± 0.242 mg • min-1 • cm-2,p = 0.023) than for the bursting stimuli (0.356 ± 0.244 mg • min-1 • cm-2). The sigmoidal shaped stimulus response curves, however, were significantly different (p = 0.0007). The EC50 (p = 0.0029) was higher during continuous stimulation and the Hill slope was lower (p<0.0001) during bursting stimuli. These data do not support the concept that a bursting stimulus pattern during intradermal electrical stimulation evokes a greater LSR.
Keywords: intradermal electrical stimulation; potentiation; quantitative analysis; stimulus-response curves.