# Autonomic Nervous System Activity in Young Subjects Exposed to Orthostatic Posture and Emotional Visual Stimuli: A Pilot Study

## TL;DR

This pilot study explores how young adults' autonomic nervous system responds to standing and emotional images, finding differences linked to sex and anxiety.

## Contribution

The study identifies sex- and anxiety-related patterns in autonomic responses to emotional stimuli and orthostatic challenges in young adults.

## Key findings

- Orthostatic challenge caused significant sympathetic activation and increased spectral HRV parameters, especially in males.
- Anxious females showed higher heart rates during positive image exposure, while non-anxious females responded more to negative images.
- Emotional stimuli modulated autonomic balance without altering heart rate, suggesting sex- and anxiety-dependent autonomic modulation.

## Abstract

Heart rate variability reflects the activity of the autonomic nervous system and serves as a physiological marker of emotional responsiveness. It indicates the functional connection between the heart and the central nervous system regions involved in regulating emotion and behavior. According to the heart rhythm coherence hypothesis, vagal afferent signaling contributes to emotional self-regulation, while negative emotions reduce vagally mediated heart rate variability. Large-scale biofeedback data confirmed associations between heart rate variability parameters and self-reported emotional states. In this study, heart rate variability analysis revealed distinct autonomic nervous system responses to orthostatic and emotional challenges in young healthy adults. Heart rate increased only during standing, indicating sympathetic activation, while emotional visual stimuli modulated autonomic balance without altering heart rate. Spectral parameters were lowest at rest and increased significantly during standing and image exposure, particularly in males, whereas parasympathetic indices showed opposite trends. Sex and anxiety appeared to be associated with differences in autonomic responses: anxious females exhibited higher heart rate during positive image exposure, while non-anxious females responded more to negative stimuli. Normalized coherence correlated positively with the low-to-high frequency power ratio across active conditions, supporting their potential role as markers of cardiac–autonomic integration and emotional adaptability.

Heart rate variability (HRV) reflects autonomic nervous system (ANS) activity and provides insight into physiological and emotional regulation. Evaluating HRV during postural and emotional challenges may help characterize autonomic adaptability in healthy individuals. HRV was recorded in 24 young medical residents (17 females, 7 males; mean age 27.04 ± 1.97 years) during four conditions: rest, orthostatic standing, and exposure to positive and negative emotional images. Each session lasted five minutes. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale. Heart rate increased significantly only during standing, consistent with sympathetic activation with postural change. Spectral and normalized HRV parameters (nLF, nlf, LF/HF, and normalized coherence) were lowest at rest and increased during standing and emotional image exposure, particularly in males. Parasympathetic indices showed opposite trends. Emotional image exposure did not produce significant differences between positive and negative valence at the group level; however, sex- and anxiety-related patterns emerged. Females with anxiety showed increased heart rate during positive image exposure, whereas non-anxious females exhibited higher heart rate responses to negative images. Orthostatic challenge elicited the strongest autonomic response, whereas emotional visual stimuli induced subtler, sex- and anxiety-dependent autonomic modulation without overall changes in heart rate. These preliminary observations suggest that anxiety and sex may be associated with differences in cardiac autonomic regulation in young healthy adults. These results should be interpreted cautiously, given the pilot design, the small sample size (N = 24), the imbalance between sexes, the exclusion of the depression subgroup from inferential analyses, and the use of non-validated emotional visual stimuli