Abstract
In order to find a stress indicator that can be used to monitor stress with wearables, we compare the almost instantaneous effects of psychological stress on skin conductance, with the effects on the stress hormone cortisol, peaking about 20-30 min later. We modelled this relation deploying a convolution of the height of the skin conductance peaks with the cortisol stress response curve, and used it to determine a skin conductance-derived estimate of stress-induced cortisol. We then conducted a first experiment to validate this model, comparing the stress-induced cortisol estimates with cortisol as measured in saliva samples. Participants (N=46) completed stressful, boring, and performance tasks in a controlled laboratory setting. Salivary cortisol samples were taken at regular moments. Based upon the pattern of measured salivary cortisol before and after the performed stressful task we divided subjects in high-cortisol responders and low-cortisol responders. For both groups, we found substantial correlations between the skin conductance-based stress-induced cortisol estimates and the measured salivary cortisol. In addition, the (Fisher-corrected) mean within-participant correlation between these variables was found to be 0.48 which proved to be significantly different from zero. These findings support the use of the skin conductance-based stress-induced cortisol estimates as a stress indicator reflecting in-body cortisol levels.
Highlights
Psychological stress—which comprises cognitive, emotional, and psychosocial stress—can compromise health when not adequately dealt with
Since cortisol is known to peak after a delay of 20–30 min, the M1 sample taken the beginning of the Psychomotor Vigilance Task (PVT) task, reflects the stress evoked 20–30 min earlier at the beginning of the experiment when participants arrived at the test room
We presented a calculation model to estimate the stress-induced changes in cortisol level from skin conductance measurements, inspired by the observation that a stressful event is usually directly followed by an increase in skin conductance, and after about 20–30 min by an increase in cortisol level
Summary
Psychological stress—which comprises cognitive, emotional, and psychosocial stress—can compromise health when not adequately dealt with. The presence and timing of a stressful event is determined from a steep increase (e.g., a peak) in skin conductance, and the strength of the stress of such an event is estimated from the height of this skin conductance increase When such a steep skin conductance increase is detected, our model assumes that this is the start of a gradual increase (and subsequent decay) of bodily cortisol following the cortisol response curve described above. Our Estimation of the level of Stress-Induced Cortisol (ESIC) is calculated by accumulating all FIGURE 2 | Parameterized CoRe cortisol response curves for males (solid line) and females (dashed line) after prolonged exposure (20 min) to, amongst others, the Trier Social Stress Test. While we do not anticipate that the estimated cortisol values are identical to the actual cortisol values in absolute level, we hypothesize that a correlation between the two may be present
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