Abstract
The aim of this study was to evaluate psycho-physiological effects of two postures on emotional states, in relation to the autonomic responses obtained from measures of heart rate variability and salivary cortisol. This study compared a sitting posture with a 7 degree head-down-tilted (7° HDT) condition. The study assessed anxiety states during the HDT conditions. Twenty-eight healthy volunteers (university students) participated (age = 20.9±1.5). The participants were divided into two groups, high-anxiety and normal, based on state trait anxiety inventory (STAI) scores. A simple protocol for monitoring electrocardiograms (ECGs) was applied for all participants, such that they first quietly adopted the sitting posture for 20 minutes, followed by a subsequent 7° HDT posture was then assumed on a tilting bed for another 20 minutes. At the end of each period, a saliva sample was collected from the participant to measure cortisol concentration and salivary buffering action. Affect-grid scoring was applied to evaluate participant's emotional states. Heart rate variability was calculated to evaluate the balance of autonomic nervous system activities (LF/HF). When the HDT posture was assumed, the high anxiety group showed significantly higher salivary cortisol levels, increases in 0.39 ± 0.35 μg/dl from 0.24 ± 0.22 μg/dl (p<0.05), as well as LF/HF ratios when compared to the sitting posture, increases in 32.68 ± 42.98 from 6.89 ± 9.80 (p<0.05). However, salivary buffering action did not show any significant changes across the postures or groups. Participant's emotion, both of pleasantness and arousal, showed significant changes between postures. These results suggest that the STAI is a useful component of a psycho-physiological evaluation gravitational tolerance and/or adaptability to a microgravity environment.
