Use of skin resistance to detect steady-state rest condition in a subject during cardiovascular measurements

Currently there is no established approach to identify the steady-state rest condition of a subject during the baseline recording in cardiovascular experiments. In this study we investigated the possibility to use the skin resistance (SR) signal to obtain such an information in a simple way. SR is known to be related to the sympathetic activity and to the level of relaxation of the subject but its magnitude may largely varies among subjects. Thus to identify the steady-state rest condition in a given subject, we need a sort of "SR calibration curve" from which the phase of stable relaxation could be easily identified. In this paper we propose a simple experimental set up aimed at creating such a "calibration curve". This approach required a modification of the traditional scheme of the hardware used for SR measurement and the definition of an ad-hoc experimental protocol in which SR could be evaluated while the subject is under stress and during relaxation. Application of this procedure on 15 subjects showed that in 12 subjects the proposed experimental set up allowed obtaining SR curves characterized by similar shapes which all included a clear fiducial point indicating the zone of stable relaxation.