HRV Interventions

Methods

108 healthy adults, randomized controlled trial, 4 intervention arms, 28 days

Key Findings

• Cyclic sighing increased RMSSD by approximately 12%
• Positive mood improvements persisted even on non-practice days
• Box breathing showed smaller but still significant improvements
• Mindfulness meditation was least effective for HRV specifically

Limitations

Self-reported compliance, predominantly young healthy adults, no long-term follow-up

Methods

Review of biofeedback literature and clinical protocols

Key Findings

• Resonance frequency is typically 4.5-7 breaths per minute for most adults
• Breathing at resonance frequency maximizes respiratory sinus arrhythmia
• Effects are immediate and measurable within a single session
• Regular practice leads to sustained improvements in baseline HRV

Limitations

Individual resonance frequency requires testing to determine precisely

Methods

Meta-analysis of 18 RCTs examining HRV biofeedback for mental health

Key Findings

• Medium effect size (d = 0.5-0.6) for depression symptom reduction
• HRV improvements correlated with mood improvements
• 6-10 sessions typically needed for meaningful benefit
• Effects maintained at follow-up in most studies

Limitations

Varied biofeedback protocols and control conditions

Methods

Review of cold exposure studies measuring autonomic response

Key Findings

• Cold triggers dive reflex and vagal activation
• HRV increases acutely during and after cold exposure
• 2-3 minutes of cold exposure sufficient for effect
• Regular practice may enhance stress resilience over time

Limitations

Long-term studies on habitual cold exposure and HRV are limited

Methods

Systematic review and meta-analysis of remote HRV biofeedback studies

Key Findings

• Medium effect size (g = 0.41) for depression improvement
• Similar effects for anxiety and stress reduction
• HRV itself also improved (g = 0.44)
• Remote delivery as effective as in-person for many outcomes

Limitations

Varied protocols and control conditions across studies

Methods

Controlled study with HRV and eye-tracking measurement before/after mindfulness

Key Findings

• Significant reduction in perceived stress after intervention
• Improved cognitive flexibility
• No immediate significant HRV change
• Attention and inhibitory control also unchanged acutely

Limitations

Single session, may need longer practice for HRV effects