Effects of Brief Heart Rate Variability Biofeedback on Physiological and Emotional Responses

**Study Background and Objectives**

This randomized, two-arm, single-session laboratory study was conducted at the University of Haifa, Israel, to investigate the immediate cardiac, forehead physiological, and affective responses to heart rate variability biofeedback (HRV-B).

The study examined whether a brief session of HRV biofeedback would produce different physiological and emotional responses compared with a time-matched psychoeducational control condition.

The original research proposal was entitled "Immediate Effects of a Single HRV Biofeedback Session on Cortical Activity and Systemic Inflammation."

The study received approval from the University of Haifa Ethics Committee for Research with Human Participants on December 29, 2025 (Approval No. 518/25). All participants provided written informed consent.

**Participants and Study Design**

The original research proposal planned the recruitment of up to 50 adult participants. Actual enrollment was 32 participants, randomly assigned to two groups using computerized random-number generation:

• HRV Biofeedback Group: 16 participants.
• Psychoeducational Control Group: 16 participants.

Each participant attended a single laboratory session lasting approximately 60 minutes.

Participants completed background and personality questionnaires and baseline assessments before the intervention, followed by physiological and psychological measurements during and after the experimental procedure.

**HRV Biofeedback Intervention**

Participants in the intervention group received a brief introduction to slow diaphragmatic breathing.

They then completed 10 minutes of HRV biofeedback using the emWave Pro Plus system (HeartMath), including a visual hot-air-balloon feedback game.

Participants were encouraged to regulate their breathing while observing real-time cardiac coherence feedback. Breathing adjustments were self-paced and guided by the visual feedback.

No individualized resonance-frequency determination, externally prescribed respiratory rate, or fixed inhalation-to-exhalation ratio was implemented.

**Psychoeducational Control Condition**

Participants assigned to the control group watched four consecutive educational videos lasting approximately 10 minutes in total.

The videos introduced general biofeedback principles, heart rate variability biofeedback, diaphragmatic breathing, and variations in breathing patterns.

Control participants did not receive real-time physiological feedback and were not instructed to perform guided biofeedback training during the videos.

**Cardiac Physiological Measurements**

Heart rate variability measurements were obtained using the emWave Pro Plus system with an earlobe photoplethysmographic sensor.

Measurements were collected during three periods:

• PRE: approximately 5 minutes before the intervention.
• DURING: 10 minutes during the intervention or control condition.
• POST: approximately 5 minutes after the intervention.

Recorded variables included heart rate, SDNN, RMSSD, total spectral power, very-low-frequency power, low-frequency power, high-frequency power, LF/HF ratio, and device-derived cardiac coherence.

**Forehead Hemoencephalography Measurements**

Forehead physiological signals were assessed using a BioTekna hemoencephalography (HEG) sensor positioned at Fpz.

Four approximately five-minute measurement periods were obtained:

• PRE: before the intervention.
• Block 1: first five minutes of the intervention.
• Block 2: second five minutes of the intervention.
• POST: after the intervention.

The exported variables included device-derived rCBO2 measures, within-record signal slope, and the proprietary CFB index.

These indices represent device-derived forehead physiological signals and were not independently validated as direct measurements of neuronal activation or absolute cerebral blood flow.

**Psychological Measurements**

Positive and negative affect were assessed immediately before and after the experimental session using the 10-item short version of the Positive and Negative Affect Schedule (PANAS).

Baseline personality characteristics were assessed using the Ten-Item Personality Inventory (TIPI).

**Originally Planned Inflammation Assessment**

The original ethics-approved research proposal included a non-invasive bioimpedance-based assessment of systemic inflammation using the BioTekna TomEEX system.

This planned measurement component was omitted from the implemented study. No bioimpedance-based inflammation assessments were performed, and no inflammation-related measurements or outcomes were collected or analyzed.

The completed study therefore included cardiac, forehead HEG, and psychological measurements, without an inflammatory measurement component.

**Statistical Analysis and Registration**

The original research proposal described a mixed-design analysis focusing on Group-by-Time interactions, with additional analyses of associations between physiological and psychological variables and possible personality-related differences in intervention responses.

The completed study used repeated-measures analyses to examine group-specific trajectories across the measurement periods. Additional exploratory analyses and post hoc sensitivity analyses were conducted.

The present ClinicalTrials.gov record was created retrospectively, after completion of participant enrollment and data collection. No prospective public trial registration was completed before enrollment.