• Pedro Schestatsky, Josep Valls-Solé, João Costa, Lucia León, Misericordia Veciana, and Márcia L Chaves.
• Medical Sciences Post-Graduation Course, UFRGS School of Medicine, Porto Alegre, Brazil. pedro.schestatsky@gmail.com
• Clin. Auton. Res. 2007 Dec 1;17(6):349-55.

ObjectiveQuantitative sensory testing (QST) is a subjective method of assessing thermal sensation, but it does not provide an objective measure of physiological changes. Our aim was to establish whether fluctuations in sudomotor autonomic activity correlate with warmth and heat pain (thermoalgesic) perception.MethodsWe conducted various thermal stimuli protocols in 22 healthy volunteers and recorded the visual analog scale (VAS) and sudomotor activity using surface electrodes attached to the hand. Sympathetic skin responses (SSR) and the mean level of electrodermal activity (EDA) were measured. EDA was analyzed by looking at the four VAS-based phases, which were divided into segments defined by the relevant psychophysical markers.ResultsIn all stimuli paradigms, the mean delay time of the SSR was 1.6 s after the warmth or pain sensation. There was an association between the low amplitude (predominantly negative) SSR and warm stimuli, and the large amplitude (predominantly positive) SSR and heat pain stimuli (chi-square; P < 0.05). Mean EDA was significantly higher during the pain phase in comparison with pre-perception, warmth and post-perception phases. INTEPRETATION: Thermoalgesic stimuli induce reflex changes in sudomotor activity that correlate with subjective perception of warmth and heat pain sensations. This association may be useful in clinical practice.

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