BS09. Latency of the skin vasomotor reflex of the finger to an electrical stimulus to the median nerve

Abstract

Introduction An electrical pulse to a sensory or mixed peripheral nerve elicits activation of the skin sympathetic response (SSR) and the latency and the duration of the response can thereby be attained. We reasoned that an electrical stimulus may also activate the sympathetic C fibers to the skin blood vessels of the hand and the latency and duration of the skin vasomotor reflexes (VSRs) could also be obtained. Methods We evaluated 30 healthy subjects aged 20–35 years. The subjects had no history of peripheral or central nervous system disease. A 0.5 ms pulse with an intensity four times the threshold was delivered to the right median nerve at the wrist. The stimulus was given at random every 40–60 s. We gave three stimuli to each subject. We recorded the SSR in the palm of the left hand and the VSRs in the tip of the left index finger. The pulsatile skin blood flow (SBF) was recorded with an infrared photoplethysmograph located at the pad of the right index finger. Results All subjects displayed both a SSR and a VSR. The mean latency of the SSR was 1.3 ± 0.3 s with a mean duration of 5.9 ± 0.6 s. The mean latency of the VSR (first decreased pulse) was 3 ± 0.5 s and the mean duration of the VSR was 9.5 ± 2 s. The VSR had a longer latency and lasted more than the SSR. The decrease in the amplitude of the SBF had a mean or 50 ± 8 per cent of the basal flow. Conclusion The SSR and VSRs reflect sympathetic C fibers traffic to the eccrine sweat glands and the skin microcirculation, respectively. The longer latency of the VSRs, compared to the SSR, may reflect a slower conduction time of the sympathetic C fibers to the skin blood vessels or be the consequence of the physiological properties of the response of the neuro-effector junction of the skin blood vessels. This technique allows a quantitative measurement of the latency and duration of the VSRs and is potentially useful for the study of peripheral and central autonomic disorders.