The Influence of Breathing on Human Heart Rate
Breathing directly influences heart rate through respiratory sinus arrhythmia, where heart rate increases during inspiration and decreases during expiration, primarily mediated by parasympathetic nervous system activity. 1
Physiological Mechanisms
Respiratory Sinus Arrhythmia (RSA)
- During normal breathing, heart rate increases during inspiration and decreases during expiration 1
- This phenomenon, known as respiratory sinus arrhythmia, is primarily modulated by cardiac parasympathetic (vagal) outflow 1
- In healthy individuals over 50 years, heart rate variability during deep breathing (expiratory/inspiratory index) should be ≥15 beats per minute 1
Autonomic Nervous System Regulation
- Breathing affects heart rate through two primary autonomic pathways:
Parasympathetic Pathway:
Sympathetic Pathway:
Heart Rate Variability (HRV) Components
Time Domain Measures
- Standard deviation of normal R-R intervals
- Root-mean square of differences between successive R-R intervals (rMSSD)
- Number of instances per hour where consecutive R-R intervals differ by >50ms (pNN50) 1
- These primarily reflect parasympathetic activity 1
Frequency Domain Measures
- High-frequency component (0.15-0.45 Hz): Primarily reflects parasympathetic activity and is synchronized with respiration 1
- Low-frequency component (0.04-0.15 Hz): Reflects a mix of sympathetic and parasympathetic influences 1
- The ratio of low-frequency to high-frequency power (LF/HF ratio): Used as a relative indicator of sympathetic modulation 1
Effects of Different Breathing Patterns
Slow Deep Breathing (<10 breaths/minute)
- Increases overall heart rate variability 3, 4
- Enhances parasympathetic activity 3, 4
- Decreases heart rate 3
- Strengthens cardiorespiratory coupling 5
- May reduce blood pressure 5, 6
Controlled Breathing
- At normal rates (15 breaths/minute or 0.25 Hz): May actually decrease parasympathetic activity compared to spontaneous breathing due to required mental concentration 7
- At slow rates (6 breaths/minute or 0.10 Hz): Significantly increases LF/HF ratio as high-frequency components shift into the low-frequency band 7
Breathing Mechanisms in Autonomic Regulation
- Slow deep breathing activates stretch receptors in the lungs (slowly adapting stretch receptors or SARs) 6
- These receptors send inhibitory signals that can synchronize neural elements in the heart, lungs, limbic system, and cortex 6
- This synchronization promotes parasympathetic dominance 6
Clinical Implications
Measurement Considerations
- Respiratory pattern should be evaluated before spectral HRV analysis to correctly interpret autonomic regulation 7
- Controlled breathing at 15 breaths/minute may inhibit parasympathetic activity due to mental concentration 7
- Controlled breathing at 6 breaths/minute may cause misinterpretation of LF/HF ratio 7
Therapeutic Applications
- Slow breathing techniques (pranayama) may beneficially affect cardiovascular autonomic regulation 3
- Regular practice may strengthen cardiorespiratory coupling 5
- Can be used to draw upon cardio-vagal reserve in various cardiovascular conditions 3
Important Caveats
- Individual responses to breathing patterns vary significantly 5
- Age affects the magnitude of respiratory sinus arrhythmia 1, 2
- Speaking during recordings can create artifacts in heart rate measurements 1
- Interpretation of HRV components becomes difficult when overall variability is very low (as in severe heart failure) 1
- The absolute power in low-frequency band should not be used as an index of sympathetic activity 1