How breath-control can change your life: A systematic review on psycho-physiological correlates of slow breathing - Zaccaro et al. (2018)
Key Points
Slow breathing increases heart rate variability, respiratory sinus arrhythmia, and alpha brain wave activity
These physiological changes lead to improved behavioral outcomes
The nose links slow breathing to these positive physiological and psychological outcomes
The Breathing Diabetic Summary
I think this paper wins “Best Title Ever” award!
This was a review study that pulled together all of the scientific literature on slow breathing and psychological/behavioral outcomes. They were trying to answer the following question: What physiological changes are common to all slow breathing studies that have shown improvements in stress and anxiety?
After using some rather rigorous criteria for their literature search, they reduced 158 potential papers down to only 15.
The physiological outcome parameters they focused on were heart rate variability (HRV), respiratory sinus arrhythmia (RSA), and brain wave activity. The studies they examined also used several different subjective questionnaires to assess stress, anxiety, depression, and well-being.
As it is with science, there was a lot of nuance and many contradictory findings. However, several common results did emerge.
First, slow breathing was associated with increases in HRV, particularly in the low frequency (LF) band. Second, it was associated with increases in RSA. Finally, slow breathing was associated with increases in alpha brain wave activity (brain waves associated with “flow”) and decreases in theta brain wave activity.
All of these common physiological changes observed during/after slow breathing were associated with improved psychological and behavioral outcomes. For example, several studies showed reductions in anxiety, improvements with depression, reduced anger, and increased relaxation.
Thus, slow breathing consistently increases HRV, RSA, and alpha brain wave activity. These physiological changes then improve psychological and behavioral outcomes.
From a practical perspective, all of the studies used breathing rates of 3-6 breaths/min. With practice, we can use an app (such as Breathing Zone) to achieve these rates.
Lastly, they examined the importance of the nose. They reviewed studies showing that nasal breathing has a direct relationship with brain activity, which goes away when the nasal cavity tissue is numbed. Moreover, certain areas of the brain follow oscillations that match breathing…but only with nasal respiration. In fact, simply puffing air into the nostrils activates the brain at those “puff” oscillations (independent of actually breathing).
The authors hypothesize that the nose is the link between slow breathing, brain and autonomic functioning, and positive emotional outcomes.
From all of this, we find that slow breathing through the nose at 3-6 breaths/min (Principle 2) has positive effects on HRV, RSA, and brain wave activity. These benefits then lead to improved psychological and behavioral outcomes.
Abstract from Paper
Background: The psycho-physiological changes in brain-body interaction observed in most of meditative and relaxing practices rely on voluntary slowing down of breath frequency. However, the identification of mechanisms linking breath control to its psychophysiological effects is still under debate. This systematic review is aimed at unveiling psychophysiological mechanisms underlying slow breathing techniques (<10 breaths/minute) and their effects on healthy subjects. Methods: A systematic search of MEDLINE and SCOPUS databases, using keywords related to both breathing techniques and to their psychophysiological outcomes, focusing on cardio-respiratory and central nervous system, has been conducted. From a pool of 2,461 abstracts only 15 articles met eligibility criteria and were included in the review. The present systematic review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: The main effects of slow breathing techniques cover autonomic and central nervous systems activities as well as the psychological status. Slow breathing techniques promote autonomic changes increasing Heart Rate Variability and Respiratory Sinus Arrhythmia paralleled by Central Nervous System (CNS) activity modifications. EEG studies show an increase in alpha and a decrease in theta power. Anatomically, the only available fMRI study highlights increased activity in cortical (e.g., prefrontal, motor, and parietal cortices) and subcortical (e.g., pons, thalamus, sub-parabrachial nucleus, periaqueductal gray, and hypothalamus) structures. Psychological/behavioral outputs related to the abovementioned changes are increased comfort, relaxation, pleasantness, vigor and alertness, and reduced symptoms of arousal, anxiety, depression, anger, and confusion. Conclusions: Slow breathing techniques act enhancing autonomic, cerebral and psychological flexibility in a scenario of mutual interactions: we found evidence of links between parasympathetic activity (increased HRV and LF power), CNS activities (increased EEG alpha power and decreased EEG theta power) related to emotional control and psychological well-being in healthy subjects. Our hypothesis considers two different mechanisms for explaining psychophysiological changes induced by voluntary control of slow breathing: one is related to a voluntary regulation of internal bodily states (enteroception), the other is associated to the role of mechanoceptors within the nasal vault in translating slow breathing in a modulation of olfactory bulb activity, which in turn tunes the activity of the entire cortical mantle.
Journal Reference:
Zaccaro A, Piarulli A, Laurino M, et al. How Breath-Control Can Change Your Life: A Systematic Review on Psycho Physiological Correlates of Slow Breathing. Front Hum Neurosci. 2018;12:353.