At the heart of most pranayama exercises is the act of slow breathing, and thankfully, there has been a decent amount of research on slow breathing. Between 12 and 20 breaths per minute is considered the normal respiratory rate for healthy adults (Flenady, Dwyer, and Applegarth 2017). So, anything less would be considered a consciously slowed-down breathing rate. But why is slow breathing deemed to be good for us? Scroll on to find out more, in an exclusive excerpt from The Physiology of Yoga.

While researchers do not yet understand the exact reasons why, it is well established that the experience of emotions has whole-body effects (Cacioppo et al 2000) and that breath is strongly linked with emotions in part via the autonomic system (Kreibig 2010). We can all attest to this. Feeling low or anxious elicits a certain breathing response in the body, while feeling elation elicits another. It is little wonder that the original Latin word for inspiration has taken on an emotionally evocative meaning while the original Latin word for expiration has taken on quite another.

The autonomic nervous system is the part of the nervous system that supplies the internal organs such as the blood vessels, stomach, intestine, liver, kidneys, bladder, heart, and digestive glands, thus influencing many involuntary functions such as heart rate, blood pressure, respiratory rate, digestion, and sexual arousal. It has two primary branches: the sympathetic, commonly referred to as the fight-or-flight response but also necessary for mobilizing our organism; and the parasympathetic, commonly called the rest-and-digest response, which elicits feelings of relaxation.

Several reviews have looked at the available evidence on the effects of slow breathing and to better understand the psychological and physiological effects of slow breathing. The reviews generally agree that slow-breathing practices like pranayama activate a parasympathetic, or calming, effect in the practitioner. The most recent was a 2018 systematic review of all the literature on slow breathing. In this review, Andrea Zaccaro at the University of Pisa and colleagues looked at the effects of slow breathing (10 breaths per minute or fewer) in healthy people and the possible psycho-physiological mechanisms behind those effects in an article titled How Breath-Control Can Change Your Life (2018). They found evidence that slow-breathing techniques increase mental and physiological flexibility, parasympathetic activity, and central nervous system activities related to emotional control and psychological well-being.

They found that slow-breathing techniques at the rate of six breaths per minute had the most reliable associations with parasympathetic activity, as measured with increased heart rate variability; increased alpha waves, as measured with electroencephalogram (ECG); and positive psychological and behavioral effects (Zaccaro et al 2018). Slow breathing has also been shown to cause near-complete inhibition of sympathetic activity (Seals, Suwarno, and Dempsey 1990), meaning that the neurons connected to the activation mode (fight-or-flight mode) are almost completely switched off.

Zaccaro and colleagues (2018) included studies that tested yogic pranayama, a Zen breathing practice, and general slow-paced breathing techniques. Unfortunately, because many of the yoga-based studies had low-quality methodologies, only one pranayama study could be included. The researchers found, as previous researchers have, that the “brand” of breathing technique did not seem to matter much because, “In our opinion, it is possible that certain meditative practices and slow-breathing techniques share, up to a point, similar mechanisms” (Zaccaro et al 2018, p. 12). Conversely, irregular breathing such as shallow or deep, rapid breathing with periods of apnea, which is the cessation of breathing, leads to increases in sympathetic activity (Leung et al 2006).

All these findings offer prime examples of how breathing directly affects our autonomic nervous system. As for the mechanism behind this connection, Zaccaro and colleagues (2018) suggested that the epithelium (the skin) on the inside of the nostrils may play an important role in the act of slow breathing causing autonomic changes. Evidence from both animal models and humans support the hypothesis that nostril-based breathing, which stimulates certain receptors in the nostril epithelium, could be one of the pivotal mechanisms behind our breath affecting our mood.

Parasympathetic nerves fire during expiration, contracting and stiffening airways to prevent collapse. Therefore, by lengthening our exhalation, we can directly target our parasympathetic nervous system. This is also why our heart rate naturally decreases with every exhalation (and naturally increases with every inhalation due to sympathetic nervous system activation). Singing, playing wind instruments, chanting, pranayama, and yoga can all stimulate the parasympathetic nervous system in this way.

While many people tend to feel more relaxed when taking slower breaths, this might not be so for everyone. Similarly, telling someone to “just breathe” or to “just relax” might not be as comforting as the speaker might intend. It is important to learn what works for us and what does not so that we can have these tools to calm ourselves down in difficult situations. In that way, understanding our breathing helps us understand ourselves.

References:

Cacioppo, J.T., G.G. Bernston, J.T. Larsen, K.M. Poehlmann, and T. Ito. 2000. The Psychophysiology of Emotion. 2nd ed. New York: Guilford Press. 

Flenady, T., T. Dwyer, and J. Applegarth. 2017. “Accurate Respiratory Rates Count: So Should You!” Australasian Emergency Nursing Journal 20 (1): 45-47.

Kreibig, S.D. 2010. “Autonomic Nervous System Activity in Emotion: A Review.” Biological Psychology 84 (3): 394-421. https://doi.org/10.1016/j.biopsycho.2010.03.010.

Seals, D.R., N.O. Suwarno, and J.A. Dempsey. 1990. “Influence of Lung Volume on Sympathetic Nerve Discharge in Normal Humans.” Circulation Research 67 (1): 130-141.

Zaccaro, A., A. Piarulli, M. Laurino, et al. 2018. “How Breath-Control Can Change Your Life: A Systematic Review on Psycho-Physiological Correlates of Slow Breathing.” Frontiers in Human Neuroscience 12 (September 7): 353. https://doi.org/10.3389/fnhum.2018.00353.