The pattern of the electrodermal activity as indicator of stress related reaction.

The aim of the present study was to characterize the patterns of signals associated with noninvasively detected skin sudomotor transient reflexes in a group of 221 apparently healthy people, aged between 16 and 72 years. By means of two pairs of surface electrodes applied respectively to the palm of the hand and to the sole of the foot skin impedance changes were recorded as two electrodermal parameters: skin electrical resistance and skin electrical capacitance. The recordings were obtained under standard conditions initially in the basal resting state of the subject and then, after the application of some standardized stimuli (evoked electrodermal responses). In terms of the basal (spontaneous) electrodermal activity and the evoked responses the subjects were divided into three categories: I--those with a high threshold of sympathetic activation (quiet basal trace and ample evoked responses); II--those with a medium threshold for sympathetic activation (basal trace with some spontaneous electrodermal activity, but obviously of a lower amplitude than the evoked responses); III--those with a low threshold for sympathetic activation (a tracing showing frequent, larger spontaneous sympathetic discharges from which the evoked responses cannot be distinguished). Of the 221 subjects, 22.2% in group I, 69.2% were included in group II, and 8.6% in group III. Our data show that each individual presents a characteristic electrodermal pattern which expresses the degree of stability/instability of the sympathetic nervous system, the most sensitive component of the physiological stress reaction system.