Deep breathing is calming and helps to clear the mind. It’s why we say to ‘take a few deep breaths’ before something stressful. But it’s not just our psychology that is influenced by deep breathing, our physiology benefits as well. Research over the last three decades has found that the stress response, also called the fight-or-flight response, is relaxed through deep breathing. What we typically feel as stress is due to high baseline flight-or-flight activity – tense muscles, a churning gut, heightened alertness, to name a few – giving the sense that we are in danger. Deep, controlled breathing relaxes this response and rebalances the nervous system. But it is a specific type of controlled breathing that creates relaxation, and the key to why and how this happens lies with the heart.
The heart is not a metronome, but constantly changes tempo, in a semi-chaotic way. Breathing has the greatest sway over variations in the heart’s tempo – during inhalation the heart beats faster, and then slower during an exhalation, a cycle known as respiratory sinus arrhythmia (RSA). During a slow, deep breath, respiratory sinus arrhythmia is more pronounced, and can be measured as an increase in a metric called Heart Rate Variability (HRV). This is the spread across the swings in heart rate, the maximum occuring around the time of a full inhale the minimum at full exhale. Perhaps unintuitively, higher HRV is healthier, in fact numerous studies over the last three decades have shown high HRV correlates with better emotional and physical resilience [1,5]. More importantly, in the research there was another significant finding: that HRV can be trained.
Heart rate swings during inhale and exhale shown in red. Heart rate variability increases when breathing is slowed to six breathes per minute, following the yellow pacer line. (Image from the Heartspace App)
When people are shown a live graph of heart rate, and told to slow their breathing to increase the swings in their heart rate, most people can quickly find a comfortable rate that maximises HRV. The max usually occurs at about six breaths per minute, around 3x slower than most people’s baseline rate. This process, called Heart Rate Variability Biofeedback Training (HRVBT), has been shown to have a large effect on reducing anxiety according to a meta-analysis of 24 studies, across 484 participants [2].
It’s because of the consistent and significant effects on wellbeing that interest in HRVBT is growing in the research community. The number of studies published on HRVBT grew exponentially each year between 1990 and 2016. This was according to another meta-analysis, which reviewed 58 studies and found a statistically significant impact on physical and emotional conditions ranging from asthma, hypertension, and pain, to anxiety, depression, and artistic performance [5]. The ascent of HRVBT is comparable to that of exercise and mindfulness meditation in the 1950s and 1970s. In fact, a 2015 study compared these three practices, and found that Biofeedback Training is equally effective at reducing stress as mindfulness and exercise [4]. And like these other wellness practices, the mechanisms behind Biofeedback Training’s effectiveness are becoming clearer.
Heart Rate Variability reflects the activity in the autonomic nervous system (ANS), and one of the active components in this system is the well known fight-or-flight response mentioned earlier. The fight-or-flight response is controlled by one half of the ANS – the so-called sympathetic branch. The other side, the parasympathetic nervous system, controls the lesser known rest-and-digest response. Both sides are always active at low levels, and kept in balance by homeostasis, the process that maintains physiological balance [1]. The homeostatic reflex is like a thermostat, turning up and down the two sides of the ANS in response to the environment. When a door is opened and a draft let in, a thermostat turns up the heat. Similarly, in a threatening situation, the homeostatic reflex turns up sympathetic activity in the autonomic nervous system, preparing the body to fight or flight.
Stress happens when there’s no real threat, but sympathetic activity stays high – a wonky thermostat. This can be alleviated by doing things to increase parasympathetic activity, and exercise and mindfulness are popular ways to do this. But if your thermostat is keeping the heater on, you’d surely rather fix it than turn on the AC. Where HRVBT differs is that, instead of simply increasing parasympathetic activity to reduce stress in the moment, it is thought to directly stimulate and strengthen the homeostatic reflex [5].
Heart Rate Variability is one of the most insightful measures of our internal physical and emotional state. When we find it’s low, and our nervous system a bit wonky, Biofeedback Training is one of the most promising modern tools found to help.
In this video Kieran, Co-founder of Heartspace explains Heart Rate Variability Biofeedback Training and how it can be achieved with the Heartspace App
References
- Lehrer, P. M., & Gevirtz, R. (2014). Heart rate variability biofeedback: how and why does it work?. Frontiers in psychology, 5, 104242.
- Goessl, V. C., Curtiss, J. E., & Hofmann, S. G. (2017). The effect of heart rate variability biofeedback training on stress and anxiety: a meta-analysis. Psychological medicine, 47(15), 2578-2586.
- Gevirtz, R. (2013). The promise of heart rate variability biofeedback: evidence-based applications. Biofeedback, 41(3).
- Van Der Zwan, J. E., De Vente, W., Huizink, A. C., Bögels, S. M., & De Bruin, E. I. (2015). Physical activity, mindfulness meditation, or heart rate variability biofeedback for stress reduction: a randomized controlled trial. Applied psychophysiology and biofeedback, 40, 257-268.
- Lehrer, P., Kaur, K., Sharma, A., Shah, K., Huseby, R., Bhavsar, J., & Zhang, Y. (2020). Heart rate variability biofeedback improves emotional and physical health and performance: A systematic review and meta analysis. Applied psychophysiology and biofeedback, 45, 109-129.