The VRELAX study is a non-clinical sub-study within the "Decreasing Preoperative Stress to Prevent Postoperative Delirium and Postoperative Cognitive Decline in Cardiac Surgical Patients"- research program (DESTRESS; NCT05036538), which investigates non-pharmacological relaxation interventions using virtual reality and binaural auditory stimulation. In a randomized counterbalanced within-subject design, non-clinical adult participants complete two sessions separated by a 1 day intervention-free interval. A 30-minute immersive nature-based virtual reality exposure combined with gradually decreasing binaural beats (10-1 Hertz (Hz)), and a control condition without relaxation. Heart rate variability (HRV) is recorded continuously, and subjective stress is assessed before and after each condition. The primary outcome is parasympathetic activation operationalized as high-frequency (HF) power of heart rate variability. Secondary outcomes include additional HRV parameters and self-reported stress ratings. The study aims to characterize short-term relaxation effects and evaluate the feasibility of independent use in everyday settings, supporting interpretation of clinical findings of the DESTRESS trial.

Psychological stress contributes to cardiovascular risk through dysregulation of the autonomic nervous system. Immersive virtual reality environments and binaural auditory stimulation have each shown stress-reducing effects, but their combined physiological impact remains insufficiently investigated. The DESTRESS research program (NCT05036538) evaluates these interventions in cardiac surgical patients. To isolate intervention-specific mechanisms independent of medical conditions, the VRELAX study was designed as a non-clinical sub-study with a randomized cross-over design in adult participants. Each participant undergoes two experimental conditions in counterbalanced order. A 30-minute immersive nature-based virtual reality exposure combined with binaural beats decreasing from alpha to delta frequency range (10-1 Hz). And a everyday cognitive activities without relaxation intervention. Sessions are separated by a 1 day intervention-free interval to reduce carryover effects. Heart rate variability is continuously measured using a validated chest-strap sensor. Subjective stress is assessed pre- and post-condition visual analogue scales. The primary outcome is HF-power of heart rate variability as an indicator of parasympathetic activation and physiological relaxation. Secondary outcomes are additional HRV parameters (root mean square of successive differences (RMSSD), number of successive normal-to-normal intervals differing by more than 50 milliseconds (NN50), percentage of successive normal-to-normal intervals differing by more than 50 milliseconds (pNN50), normalized high-frequency power of heart rate variability (HF%)), subjective stress ratings, and feasibility of independent intervention use based on participant instruction. By investigating physiological relaxation mechanisms in a non-clinical population, the study allows interpretation of intervention-specific effects independent of disease, medication, or perioperative factors. The findings will provide mechanistic context for the clinical DESTRESS trial and evaluate whether an easily implementable immersive relaxation procedure may serve as a preventive approach for reducing everyday and work-related stress.

Inclusion Criteria:

• Adults aged 18 years or older
• Ability to understand study procedures and provide written informed consent
• Sufficient proficiency in the German language to complete questionnaires and follow study instructions
• Willingness to participate in a single approximately 60-minute study session

Exclusion Criteria:

• Current or history of neurological or psychiatric disorders that may interfere with data collection (e.g., dementia, major depressive disorder, stroke, epilepsy)
• Severe visual or hearing impairments that would limit the use of virtual reality equipment or headphones
• History of adverse reactions to virtual reality

This is an open-label study. Due to the nature of the interventions, participants and investigators are not blinded to group assignment.