Overview
This study investigates whether the psychophysiological benefits of breathing exercises are driven by a specific physiological rhythm (6 breaths per minute) or by the general psychological experience of performing a structured, mindful activity. Researchers aim to determine if "coherent breathing", which is hypothesized to synchronize heart and respiratory rhythms, offers unique physiological protection against stress compared to breathing at a natural pace or simple resting. The main questions it aims to answer are:
- Does slow, steady breathing at 6 breaths per minute lower physical stress markers (like heart rate variability and cortisol) better than faster, but structured breathing or just sitting still?
- Is the calming effect caused by the specific breathing rhythm or simply by performing a structured, relaxing activity?
Researchers will compare three groups to see if the specific rhythm of "coherent breathing" offers unique benefits:
- Group (Interventional): Coherent Breathing: Slow breathing at 6 breaths per minute.
- Group (Sham Breathing): Regular breathing at 15 breaths per minute (matching a natural pace).
- Spontaneous Breathing (Control Group): Natural, unguided breathing.
Participants will:
- Complete a one-day preparation phase to become familiar with the breathing technique.
- Visit the research center for one experimental session.
- Perform their assigned breathing method before and after a stress test.
- Take the Maastricht Acute Stress Test (MAST), which involves putting a hand in cold water and doing mental math.
- Provide saliva samples and have their heart rate variability, and mood measured multiple times.
Description
This three-arm randomized controlled trial is designed to investigate whether the therapeutic benefits of slow-paced breathing stem from specific physiological mechanisms (cardiorespiratory resonance) or non-specific psychological factors, such as attention, expectancy, and structured relaxation.
The study directly compares resonant-frequency breathing against a structurally identical sham intervention and a passive control group.
Experimental Protocol:
The study utilizes the Maastricht Acute Stress Test (MAST) as a highly structured and validated laboratory stressor to capture the dynamic psychophysiological response to acute distress.
The protocol consists of the following phases:
Baseline Phase (BASE): A 5-minute measurement of baseline physiological (HRV - Heart Rate Variability) and psychological (STAI-S - State-Trait Anxiety Inventory-State, VAMS - Visual Analogue Mood Scales) parameters.
First Intervention (10 min): Participants perform their assigned breathing technique or sit quietly to assess the preventive "buffering" effect of the intervention.
Acute Stress Induction (MAST): A 15-minute structured stressor combining periods of hand immersion in cold water and mental arithmetic under social-evaluative pressure. The water temperature is strictly maintained within the range of 4.5 - 5.5 °C using a TECO chiller to ensure consistent stress induction across all participants.
Post-Stress Recovery (POST): Immediate 5-minute measurement following the conclusion of the MAST protocol.
Second Intervention (10 min): A repeat of the breathing/control protocol to evaluate its impact on psychophysiological recovery.
Final Assessments (END \& FOLLOW): Measurements are taken immediately after the second intervention and following a 15-minute recovery phase to capture the peak glucocorticoid (cortisol) response.
Data Collection and Analysis:
- Heart Rate Variability: RR interval (time duration between successive heartbeats, specifically the time intervals between each R-wave peak) data is collected using a Polar H10 heart rate monitor. To ensure data integrity and redundancy, the signal is recorded simultaneously through two mobile applications: Elite HRV and Kubios HRV. All subsequent advanced HRV analyses, including time-domain, frequency-domain, and non-linear indices (e.g., PNS/SNS Index \[Parasympathetic Nervous System Index and Sympathetic Nervous System Index\], RMSSD \[Root Mean Square of Successive Differences\]), are performed using Kubios HRV Scientific software.
- Biochemical Markers: Salivary cortisol levels are measured to assess the hypothalamic-pituitary-adrenal (HPA) axis response using ELISA kits.
- Psychological Scales: Subjective stress and anxiety are tracked using the STAI-VAMS.
Adherence Check: Participant adherence to the paced breathing protocols is verified using the Kubios RESP (respiratory rate estimation) algorithm. This software-based solution extracts respiratory frequency from the RR interval data to confirm that participants maintained the target rates of 6 bpm (breaths per minute) or 15 bpm.
Research Arms:
- Coherent Breathing (6 bpm): Guided nasal diaphragmatic breathing (5.5 s inhale / 5.5 s exhale) focused on inducing cardiorespiratory resonance.
- Sham Breathing (15 bpm): Guided breathing at a natural pace (2 s inhale / 2 s exhale) to control for the effects of a structured intervention.
- Spontaneous Breathing (Control): Passive resting with eyes closed, serving as a neutral baseline for the natural course of the stress response.
Eligibility
Inclusion Criteria:
- Healthy adults
- Aged 18 to 60 years
- Willingness to participate in all study phases, including preparation and laboratory session.
- Professionally active individuals or university students.
Exclusion Criteria:
- Severe chronic diseases, including metabolic disorders (e.g., diabetes) and mental disorders.
- Cardiac arrhythmia, history of heart attacks, strokes, or heart surgery.
- Regular use of medications such as anxiolytics or beta-blockers (excluding hormonal contraception)
- Pregnancy.
- Current participation in other scientific experiments.
- Significant previous experience with breathing techniques or current independent breathwork/meditation practice (defined as regular practice for more than 7 days in total within the last 12 months).
- Professional sports practice.
- Raynaud's disease
- Inability to abstain from alcohol, caffeine, and nicotine for the required periods before the experiment
