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: 1. Group (Interventional): Coherent Breathing: Slow breathing at 6 breaths per minute. 2. Group (Sham Breathing): Regular breathing at 15 breaths per minute (matching a natural pace). 3. 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.
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: 1. Coherent Breathing (6 bpm): Guided nasal diaphragmatic breathing (5.5 s inhale / 5.5 s exhale) focused on inducing cardiorespiratory resonance. 2. 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. 3. Spontaneous Breathing (Control): Passive resting with eyes closed, serving as a neutral baseline for the natural course of the stress response.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
SINGLE
Enrollment
120
A 10-minute session of guided nasal diaphragmatic, coherent breathing. Participants follow rhythmic audio bell cues: a low tone for a 5.5-second inhalation and a high tone for a 5.5-second exhalation. Instructions emphasize silent, gentle nasal breathing and abdominal (diaphragmatic) expansion without lifting the shoulders. Participants are asked to focus their attention on the sensations of air flow or abdominal movement throughout the session. The intervention is performed twice: before and after the stress protocol
A 10-minute session of guided nasal diaphragmatic breathing at a rate of 15 breaths per minute (matching a natural spontaneous pace). Participants follow identical rhythmic audio bell cues as the experimental group: a low tone for a 2.0-second inhalation and a high tone for a 2.0-second exhalation. All other instructions regarding nasal breathing, abdominal mechanics, and mindful attention are identical to the experimental group to ensure structural blinding. The intervention is performed twice: before and after the stress protocol
Medical University of Bialystok. Department of Physiology.
Bialystok, Podlaskie Voivodeship, Poland
RECRUITINGChange in Root Mean Square of Successive (RMSSD)
The Root Mean Square of Successive Differences (RMSSD) measured in milliseconds (ms). This is a time-domain HRV parameter used to assess parasympathetic nervous system activity. An increase indicates higher parasympathetic activity, while a decrease indicates a stress response.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in PNS Index
This outcome measure is reported as a single composite score (standardized Z-score) representing the aggregated modulation of vagal activity. The final value is automatically calculated by Kubios HRV Scientific software from the mathematical combination of three specific assessments: mean RR interval, RMSSD, and the non-linear SD1 parameter, normalized against a reference database. Only the final aggregated Z-score will be reported as the endpoints for these measures. A value of 0 represents the population average; positive values indicate enhanced parasympathetic tone and recovery capacity.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Salivary Cortisol Concentration
Concentration Measured via enzyme-linked immunosorbent assay (ELISA) in nmol/L. This neuroendocrine marker assesses the activation of the hypothalamic-pituitary-adrenal (HPA) axis. It is used to quantify the objective impact of the breathing intervention on the peak hormonal stress response (typically reaching maximum concentration 15-30 minutes after the stressor).
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in STAI-State score
A validated self-report questionnaire used to measure the current intensity of anxiety, tension, and nervousness. Scores range from 20 to 80, with higher scores indicating greater subjective psychological distress.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Mean HR
Mean heart rate measured in beats per minute (bpm). This serves as a fundamental indicator of physiological arousal and autonomic nervous system activity.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in SNS Index
This outcome measure is reported as a single composite score (standardized Z-score) representing the aggregated physiological arousal and sympathetic activity. The final value is automatically calculated by Kubios HRV Scientific software from the mathematical combination of three specific assessments: mean heart rate (HR), Baevsky's Stress Index, and the non-linear SD2 parameter, normalized against a reference database. Only the final aggregated Z-score will be reported as the endpoints for these measures. Positive values indicate sympathetic dominance and physiological arousal, providing a quantitative measure of the "cost" of the stressor and the effectiveness of the intervention in reducing sympathetic overdrive.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Diastolic Blood Pressure (DBP)
Measured in millimeters of mercury (mmHg) using an automated sphygmomanometer. This metric serves as functional hemodynamic endpoint to verify the hypothesis that coherent breathing enhances baroreflex sensitivity and stabilizes blood pressure.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Subjective Stress (VAMS)
A specific assessment of subjective stress intensity. Participants mark their current feeling on a 100 mm visual analogue scale (0-100), where 0 indicates "no stress" and 100 indicates "maximum stress" . Only this individual scale value is reported as the endpoint for this measure.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Mean Heart Rate (Mean HR) during Experimental Blocks
Continuous monitoring of mean heart rate (bpm) during active interventions and stress induction to evaluate real-time physiological reactivity and recovery dynamics.
Time frame: Average heart rate measured during three 10-minute periods starting at approximately 10 minutes (First Intervention), 35 minutes (Stress Induction), and 55 minutes after Baseline during the single experimental Day 3.
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SNS Index during Stress Induction
This outcome measure is reported as a single composite score (standardized Z-score) representing the aggregated physiological arousal and sympathetic activity. The final value is automatically calculated by Kubios HRV Scientific software from the mathematical combination of three specific assessments: mean heart rate (HR), Baevsky's Stress Index, and the non-linear SD2 parameter, normalized against a reference database. Only the final aggregated Z-score will be reported as the endpoint for this measure.
Time frame: Average score measured during one 10-minute period starting at approximately 35 minutes (Stress Induction) after Baseline during the single experimental Day 3.
Change in Standard Deviation of NN intervals (SDNN)
A time-domain metric reflecting the total variability of heart rate rhythm, measured in milliseconds (ms). It represents the overall capacity of the autonomic nervous system to adapt to internal and external stimuli.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
SNS index during Intervention Blocks
This outcome measure is reported as a single composite score (standardized Z-score) representing the aggregated physiological arousal and sympathetic activity. The final value is automatically calculated by Kubios HRV Scientific software from the mathematical combination of three specific assessments: mean heart rate (HR), Baevsky's Stress Index, and the non-linear SD2 parameter, normalized against a reference database. Only the final aggregated Z-score will be reported as the endpoint for these measures.
Time frame: Average score measured during two 10-minute periods starting at approximately 10 minutes (First Intervention) and 55 minutes (Second Intervention) after Baseline during the single experimental Day 3.
Change in LF power log (ln LF)
The natural logarithm of the HRV absolute power in the low-frequency band (0.04 - 0.15 Hz).
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Log-transformed High-Frequency HRV Power (ln HF)
The natural logarithm of the HRV absolute power in the high-frequency band (0.15 - 0.40 Hz).
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
PNS Index during Stress Induction
This outcome measure is reported as a single composite score (standardized Z-score) representing the aggregated modulation of vagal activity. The final value is automatically calculated by Kubios HRV Scientific software from the mathematical combination of three specific assessments: mean RR interval, RMSSD, and the non-linear SD1 parameter, normalized against a reference database. Only the final aggregated Z-score will be reported as the endpoint for this measure.
Time frame: Average score measured during one 10-minute period starting at approximately 35 minutes (Stress Induction) after Baseline during the single experimental Day 3.
PNS index during Intervention Blocks
This outcome measure is reported as a single composite score (standardized Z-score) representing the aggregated modulation of vagal activity. The final value is automatically calculated by Kubios HRV Scientific software from the mathematical combination of three specific assessments: mean RR interval, RMSSD, and the non-linear SD1 parameter, normalized against a reference database. Only the final aggregated Z-score will be reported as the endpoint for these measures.
Time frame: Average score measured during two 10-minute periods starting at approximately 10 minutes (First Intervention) and 55 minutes (Second Intervention) after Baseline during the single experimental Day 3.
Change in Systolic Blood Pressure (SBP)
Measured in millimeters of mercury (mmHg) using an automated sphygmomanometer. This metric serves as functional hemodynamic endpoint to verify the hypothesis that coherent breathing enhances baroreflex sensitivity and stabilizes blood pressure.
Time frame: Measured at 5 time points: at Baseline (0 minutes), and approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Subjective Mental Tension (VAMS)
A specific assessment of subjective mental tension intensity. Participants mark their current feeling on a 100 mm visual analogue scale (0-100), where 0 indicates "no tension" and 100 indicates "maximum tension" . Only this individual scale value is reported as the endpoint for this measure.
Time frame: At Baseline (0 minutes), and at approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Subjective Calmness (VAMS)
A specific assessment of subjective calmness intensity. Participants mark their current feeling on a 100 mm visual analogue scale (0-100), where 0 indicates "no calm" and 100 indicates "maximum calm" . Only this individual scale value is reported as the endpoint for this measure.
Time frame: At Baseline (0 minutes), and at approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.
Change in Subjective Relaxation (VAMS)
A specific assessment of subjective relaxation intensity. Participants mark their current feeling on a 100 mm visual analogue scale (0-100), where 0 indicates "no relaxation" and 100 indicates "maximum relaxation" . Only this individual scale value is reported as the endpoint for this measure.
Time frame: At Baseline (0 minutes), and at approximately 25, 45, 60, and 75 minutes after Baseline during the single experimental session on Day 3.