2.5. Autonomic Parameters
SKIN, COLD
Autonomic parameters were collected by means of a portable-computer-based data acquisition system with AcqKnowledge software (BIOPAC Systems Inc., Camino Goleta, CA, USA), using a finger photoplethysmograph and electrodermal activity (EDA) transducers. They were placed on the nondominant hand of the participants. The photoplethysmograph provided data for heart rate and heart rate variability (HRV) that were analyzed with Kubios HRV software (Kubios software, Premium 3.3.1, Finland). HRV parameters of interest were the root mean square of successive differences between normal heartbeats in millisecond (RMSSD), the mean of heart rate (Mean HR), the peak in the low-frequency band (LF) (0.04–0.15 Hz), the peak in the high-frequency band (HF) (0.15–0.4 Hz), and the ratio of low-frequency to high-frequency peaks (LF:HF). The electrodermal sensor provided the Skin Conductance Level (SCL) in microsiemens. SCL was processed with AcqKnowledge software using a smoothing baseline removal with a window width of 2 s, a low-pass filter with a cutoff frequency of 1 Hz, and a linear interpolation method. The waveform was resampled to 7.813 Hz, and phasic EDA was subtracted from the signal. Both cardiac and electrodermal data were computed for periods of different lengths. They correspond to 5 min baseline before instructions were given (Before), 5 min stress anticipation (during the instructions; During 1), the average of cold hand immersions (During 2), the average of mental arithmetic trials (During 3), and 8 periods of rest after the stressor (After 1; After 2; After 3; After 4; After 5; After 6; After 7; After 8), as shown in 