2020 Meta-Analysis: Slow Breathing Improves A Variety of Behavioral and Physiological Outcomes

Key Points

• Across 58 studies and 2,485 patients, heart rate variability biofeedback (HRVB) and slow breathing improve a wide range of behavioral and physiological outcomes.

• These methods provide a simple, safe, and effective complementary therapy that could be useful in a wide variety of settings.

• Slow breathing (without biofeedback) is likely to be enough, requiring little more than a cellphone application to get started.

The Breathing Diabetic Summary

A hallmark of slow breathing is that it increases heart rate variability (HRV). It does this by increasing respiratory sinus arrhythmia (RSA), which synchronizes your heart rate with your breathing. When they match, your heart rate increases while you inhale and it decreases while you exhale.

Thus, RSA enhances the “peaks and troughs” of heart rate with each breath, which increases HRV. Because HRV is a robust indicator of overall health and wellness, this is one way in which slow breathing is so powerful. So much so, in fact, that HRV biofeedback (or HRVB) has become extremely popular to help with a variety of problems. 

With HRVB, a person’s “perfect” breathing rate is determined—that is, one that maximizes HRV. And because increases in RSA and HRV are driven by increases in the calming parasympathetic branch of the nervous system, this can reduce negative stress and increase overall resiliency. This has wide-reaching positive benefits.

We’ve covered many of them before. But here are some of the general benefits:

• Reduced blood pressure.

• Reduced stress and anxiety.

• Improved emotional control.

• Enhanced cognitive function.

• Better cardio-autonomic function.

• Improved gas exchange in the lungs.

In this meta-analysis, the authors performed an extensive literature review to examine these benefits of HRVB from a broader statistical perspective. They included papers spanning a wide range of settings, measuring a wide range of outcomes.

Note that, although HRVB sounds fancy (and it can be), many of the benefits are achieved by simply breathing at a rate of about 5-6 breaths per minute.

Therefore, this meta-analysis also included studies that used 6 breaths per minute because:

“it is possible that simply doing paced breathing at about six breaths per minute would have the same salutary effects as breathing more exactly at resonance frequency. […] This can easily be taught by following a computer-generated pacing signal or a clock.”

From a practical perspective, this might be the most important aspect of this meta-analysis.

After starting with more than 1,500 papers, they ended up with 58 studies having a total of 2,485 patients.

Their statistical analysis of all these studies revealed that HRVB and slow breathing both significantly improve many aspects of health and wellness.

The greatest benefits were for:

• Athletic performance

• Artistic performance

• Depression

• Gastrointestinal problems

• Anxiety and anger

• Respiratory disorders

• Systolic blood pressure

• Pain

Smaller, but still meaningful, benefits were found for:

• Self-reported stress

• Quality of life

• Diastolic blood pressure

• PTSD

• General energy

• Sleep

Interestingly, I would have expected several items on the second list to be on the first. But that’s why meta-analyses like this are so important : ) Also, note that measures like “self-reported stress” are harder to quantify. The authors even mention that these results might be the result of how the questionnaires were given.

In any case, the overall results of this meta-analysis are quite exceptional: HRVB and slow breathing both have wide-ranging benefits for overall health and wellness.

These two sentences from the paper sum it up better than I ever could:

“These results suggest that HRVB might be a useful addition to the skill sets of clinicians working in a variety of settings, including mental health, behavioral medicine, sports psychology, and education. The method is easy to learn and can easily be used along with other forms of intervention, with rare side effects.”

Abstract

We performed a systematic and meta analytic review of heart rate variability biofeedback (HRVB) for various symptoms and human functioning. We analyzed all problems addressed by HRVB and all outcome measures in all studies, whether or not relevant to the studied population, among randomly controlled studies. Targets included various biological and psychological problems and issues with athletic, cognitive, and artistic performance. Our initial review yielded 1868 papers, from which 58 met inclusion criteria. A significant small to moderate effect size was found favoring HRVB, which does not differ from that of other effective treatments. With a small number of studies for each, HRVB has the largest effect sizes for anxiety, depression, anger and athletic/artistic performance and the smallest effect sizes on PTSD, sleep and quality of life. We found no significant differences for number of treatment sessions or weeks between pretest and post-test, whether the outcome measure was targeted to the population, or year of publication. Effect sizes are larger in comparison to inactive than active control conditions although significant for both. HRVB improves symptoms and functioning in many areas, both in the normal and pathological ranges. It appears useful as a complementary treatment. Further research is needed to confirm its efficacy for particular applications.

Journal Reference:

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(3), 109–129. https://doi.org/10.1007/s10484-020-09466-z

Slow Breathing at Six Breaths per Minute Improves Baroreflex Sensitivity and Reduces Blood Pressure

Key Points

• Slow breathing improves baroreflex sensitivity, reduces blood pressure, and potentially reduces chemosensitivity

• Slow breathing with ujjayi is not as effective as slow breathing alone in untrained practitioners

• Choose an inhale-to-exhale ratio that is comfortable for you when practicing slow breathing

The Breathing Diabetic Summary

Slow breathing at around 6 breaths/min improves cardiovascular and autonomic functioning. For example, it increases baroreflex sensitivity (BRS), which measures your heart’s ability to adjust your blood pressure in response to changing conditions. Slow breathing also increases parasympathetic tone, leading to better autonomic balance. This study assessed two additional aspects of slow breathing.

First, it evaluated the added effect of “ujjayi” breathing. Ujjayi breathing involves tightening of the throat during the inhale or exhale to make an ocean sound (check out the Wiki article for a simple explanation). It can be somewhat challenging to learn, but many trained yogis use it exclusively during their yoga practice. 

Second, this study examined how the ratio of inhale to exhale affected cardiovascular and autonomic outcomes. Extended exhales are regularly practiced for relaxation. For example, you perform a 4 sec inhale and 8 sec exhale. However, an equal ratio has also been proven to enhance heart rate variability (for example, 5 sec inhale, 5 sec exhale). Here, they assessed these different ratios to help establish the best approach for beginners to slow breathing.

Study Details

The study had seventeen participants. Measurements were taken in the supine position while the subjects breathed spontaneously for three minutes. Then, they performed the following breathing protocols: 

• Controlled breathing at 15 breaths/min 

• Controlled breathing at 6 breaths/min with 5 sec inhale and exhale

• Controlled breathing at 6 breaths/min with 3 sec inhale and 7 sec exhale

• Both 6 breaths/min protocols, but with ujjayi.  

The order of the slow breathing was selected randomly for each subject, and there was a two-minute break between each protocol.

Slow Breathing without Ujjayi is More Effective for BRS

The results showed that all of the slow breathing techniques improved BRS. However, there was no added benefit of ujjayi and it actually worsened BRS slightly when compared to slow breathing alone. 

Slow Breathing Reduces Blood Pressure

Interestingly, slow breathing increased heart rate, except when practiced with an equal inhale/exhale.  However, slow breathing reduced diastolic and systolic blood pressures. The decrease was most significant when an equivalent inhale/exhale was used. Again, slow breathing alone outperformed ujjayi.

Slow Breathing & Chemosensitivity

Lastly, they found that slow breathing decreased chemosensitivity. However, the measurement of chemosensitivity was heuristic: it was defined as the tidal volume divided by inhale time. That is, if your tidal volume increased for a given inhale time, that would indicate an increased chemosensitivity (because you are taking a bigger breath over the same inhale time).

Conversely, they also measured end-tidal CO2, and these results showed that all versions of slow breathing significantly reduced CO2 compared to spontaneous breathing. People often overcompensate for the slow breathing rate with bigger breaths, which appears to have happened here. Consistent training or biofeedback can reduce this over-breathing.

In any case, although they concluded that slow breathing reduced chemosensitivity, the significantly decreased end-tidal CO2 does not support this finding in my opinion.

Breathe at a Ratio that is Comfortable to You

To summarize, this study found that slow breathing increased BRS and reduced blood pressure. It also reduced their measure of chemosensitivity.  Although using an equal inhale to exhale ratio showed slightly better results, they suggest that “practitioners can engage in a ratio that is personally comfortable and achieve the same BRS benefit.” 

Interestingly, ujjayi worsened the results when compared to slow breathing alone. They hypothesize that the extra effort needed for ujjayi dampened the parasympathetic response. These results would likely be different in seasoned ujjayi practitioners. 

Therefore, we can conclude that slow breathing at a rate of 6 breaths/min improves cardiovascular and autonomic function. The best way to begin is to choose a ratio that is comfortable for you.

Abstract

Slow breathing increases cardiac-vagal baroreflex sensitivity (BRS), improves oxygen saturation, lowers blood pressure, and reduces anxiety. Within the yoga tradition slow breathing is often paired with a contraction of the glottis muscles. This resistance breath "ujjayi" is performed at various rates and ratios of inspiration/expiration. To test whether ujjayi had additional positive effects to slow breathing, we compared BRS and ventilatory control under different breathing patterns (equal/unequal inspiration/expiration at 6 breath/min, with/without ujjayi), in 17 yoga-naive young healthy participants. BRS increased with slow breathing techniques with or without expiratory ujjayi (P < 0.05 or higher) except with inspiratory + expiratory ujjayi. The maximal increase in BRS and decrease in blood pressure were found in slow breathing with equal inspiration and expiration. This corresponded with a significant improvement in oxygen saturation without increase in heart rate and ventilation. Ujjayi showed similar increase in oxygen saturation but slightly lesser improvement in baroreflex sensitivity with no change in blood pressure. The slow breathing with equal inspiration and expiration seems the best technique for improving baroreflex sensitivity in yoga-naive subjects. The effects of ujjayi seems dependent on increased intrathoracic pressure that requires greater effort than normal slow breathing.

Journal Reference:

Mason H, Vandoni M, Debarbieri G, Codrons E, Ugargol V, Bernardi L. Cardiovascular and Respiratory Effect of Yogic Slow Breathing in the Yoga Beginner: What is the Best Approach?  Evid Based Complement Alternat Med. 2013;2013:743504. doi: 10.1155/2013/743504.