Resonance frequency breathing is based on the interaction of two physiological properties of the cardiovascular system: the connection between blood pressure and heart rate; and the connection between breathing and heart rate.
The link between blood pressure and heart rate
Our blood pressure changes in response to many factors, including our movement, our body position, how fast and powerfully our heart is beating, and the physical properties of our blood vessels, such as how open or closed they are and how elastic they are. Maintaining blood pressure in a safe range so that blood can be delivered to the parts of the body that need it most is critical to our health.
In the walls of the large arteries close to the heart are special receptors called “baroreceptors” that sense changes in blood pressure. Baroreceptors send signals to the brain, which then responds by sending signals to the heart to speed up when blood pressure falls, or to slow down when blood pressure rises. This control system regulating heart rate based on changes in blood pressure is called the “baroreflex” and is part of the larger control system that maintains proper blood pressure throughout the body.
The link between breathing and heart rate
In a healthy state, our heart rate changes as we breathe. When we inhale, our heart rate speeds up, and when we exhale, our heart rate slows down in a process called “respiratory sinus arrhythmia,” or RSA. The reason this happens is complex but has to do with the changes in pressure inside the chest as we breathe in and out and the fact that inhaling and exhaling are controlled by different parts of our nervous system. Respiration is controlled by a combination of two different parts of our autonomic nervous system—the sympathetic nervous system (SNS), which is more active in the inhalation phase, and the parasympathetic nervous system (PNS), which acts to dampen the activity of the SNS and is more active in the exhale phase. In healthy individuals, the activity of the SNS during inhale provides a signal to speed up the heart, while the activity of the PNS during the exhale acts to slow down the heart.
One effect of this variation is to increase the efficiency of the transfer of oxygen from the air in the lungs to the blood. As we inhale and our heart beats faster, more blood passes through the blood vessels of the lungs when the air is rich in oxygen.
Resonance of the cardiovascular system
The maintenance of blood pressure in an optimal zone via the baroreflex does not happen instantaneously; there is a delay. Due to the inertia of moving blood through the blood vessels, it takes about 5 seconds (in the average adult) for a change in heartbeat to affect a change in blood pressure throughout the entire system. Because of this delay, and the fact that there is a constant feedback loop between the changing pressure and the heart rate—when blood pressure rises, heart rate goes down, when blood pressure falls, heart rate goes up—blood pressure naturally tends to cycle, or oscillate, up and down. Systems with these characteristics exhibit the phenomenon of resonance. Resonance is the property of oscillating systems to experience a significant increase in oscillation when acted on by a force or vibration that perfectly complements the oscillations of the system.
The human cardiovascular system exhibits resonance and research has identified the resonance frequency for adults at between 4.5-7 cycles per minute. The average is around 6 cycles per minute, which means a full cycle every 10 seconds. Adding a periodic force to the cardiovascular system at this frequency results in larger variations in heart rate and blood pressure. This can be achieved many ways: by tensing and releasing muscles, changing posture by standing and sitting, or even viewing alternately exciting then calming images. The effect can also be achieved by breathing at the resonance frequency.
At the resonance frequency of our cardiovascular system, there is an interesting interplay that occurs between the changes in heart rate due to breathing and the changes in heart rate due to the baroreflex. At the resonance frequency, changes in heart rate in response to breathing happen at the same time, or perfectly ‘in phase,’ while changes in heart rate in response to changes in blood pressure happen with a half cycle delay, or perfectly ‘out of phase.’ This means that as we inhale, the increase in heart rate will cause blood pressure to rise to a peak about 5 seconds later. If we are breathing at resonance frequency, we will be starting our exhale just as blood pressure has reached a high point, so now both exhaling and higher blood pressure will combine to cause heart rate to slow down. After 5 seconds, blood pressure will be at a low point, just as we start our inhale, so now both inhaling and lower blood pressure will combine to cause heart rate to speed up. The combination of these two feedback loops oscillating at the system’s resonance frequency causes them to amplify each other. When we breathe at resonance frequency, the variations in heart rate and blood pressure oscillate with a larger amplitude than our normal baseline variations.
Takeaways: What are the benefits of resonance frequency breathing?
It turns out that enhanced oscillations of heart rate and blood pressure can have beneficial effects on our health. One important impact is an increase in the sensitivity of the baroreflex, which is generally considered a marker of cardiovascular system health, and which may have implications for blood pressure disorders. Other benefits include increased autonomic nervous system balance, through facilitating a toggling back and forth between SNS and PNS activity, which can improve symptoms of anxiety, panic disorder, and depression; and increased gas exchange efficiency, which can improve symptoms of COPD.
References:
- Khazan, Inna. Biofeedback and Mindfulness in Everyday Life: Practical Solutions for Improving Your Health and Performance. W. W. Norton & Company, 2019.
- Lehrer, Paul M., and Richard Gevirtz. “Heart Rate Variability Biofeedback: How and Why Does It Work?” Frontiers in Psychology 5 (2014). https://www.frontiersin.org/articles/10.3389/fpsyg.2014.00756.
- Lehrer, Paul M., and Robert L. Woolfolk. Principles and Practice of Stress Management, Fourth Edition. Guilford Publications, 2021.
- Lehrer, Paul M., Evgeny Vaschillo, and Bronya Vaschillo. “Resonant Frequency Biofeedback Training to Increase Cardiac Variability: Rationale and Manual for Training.” Applied Psychophysiology and Biofeedback 25, no. 3 (September 1, 2000): 177–91. https://doi.org/10.1023/A:1009554825745.