How Breathing Regulates the Cardiovascular System and Improves Chemosensitivity

Key Points

• Breathing modulates the cardiovascular system through respiratory sinus arrhythmia

• Slow breathing reduces chemosensitivity to high carbon dioxide and low oxygen

• Controlled breathing could be a beneficial intervention in different pathological states

The Breathing Diabetic Summary

How does breathing affect us physiologically?  Well, the answer to that is complex.  Breathing is felt by various receptors throughout the body, affecting cardiovascular and autonomic variability on many levels. This review study examined these different modulatory effects of breathing through a comprehensive analysis of the peer-reviewed literature.

Breathing and the Cardiovascular System

The cardiovascular system is sensitive to external stimuli. Just picture something scary (like giving a presentation), and your heart rate will likely increase. Consequently, your breathing will also change to match your metabolic needs.

But this is a two-way street. Controlled, rather than reactive, breathing also has profound impacts on the cardiovascular system. This can be temporary, for example, breathing rapidly for one minute, or permanent, for example, developing the behavior/habit of chronic over-breathing.

Knowing that breathing has "direct access" to the cardiovascular system, let's look at how this occurs and how controlled breathing might be beneficial in different pathological states.

Respiratory Sinus Arrhythmia

One way in which breathing permeates the cardiovascular system is through respiratory sinus arrhythmia (RSA). RSA is a measurement of how breathing, heart rate, and blood pressure all interact. In simple terms, RSA refers to the increase in heart rate as you inhale and decrease in your heart rate as you exhale. RSA is thought to be an index of vagal activity and direct measurement of heart rate variability.  

When we breathe so that the length of our inhale matches seamlessly with our heart rate increase and our exhale with our heart rate decrease, we maximize RSA. Typically, this occurs when breathing at around 6 breaths per minute. This coherence among respiration and heart rate leads to the maximization of heart rate variability, improving cardiovascular efficiency.

Breathing and Chemoreflexes

Slow breathing can reduce breathlessness and improve exercise performance in patients with chronic heart failure. These results suggest that slow breathing could be modifying the chemoreflexes, allowing one to tolerate higher concentrations of carbon dioxide and lower concentrations of oxygen.

To test this hypothesis, a study was conducted with yoga trainees and non-yoga trained participants. Both groups performed different breathing protocols to test their response to high carbon dioxide (hypercapnia) and low oxygen (hypoxia). Although none of these participants had heart problems, the goal was to see if slow breathing could reduce chemoreflexes in the controls to the levels seen in yoga practitioners.

As we might expect, the chemoreflexes of the yoga practitioners at baseline were much lower than the non-trained participants.  This means their breathing did not increase as much when exposed to hypercapnia or hypoxia. Interestingly, the chemoreflexes of the controls decreased to levels similar to the yogis when breathing at 6 breaths per minute.  Therefore, the simple act of slow breathing reduced chemosensitivity to carbon dioxide and hypoxia, regardless of previous training.

These results indicate that breathing could represent another way to better coordinate the breathing muscles, improve chemoreflexes, and improve exercise performance in patients with cardiovascular problems. Slow breathing could, therefore, be a practical alternative when other rehabilitation programs are not available.

Breathing Modulates Cardiovascular and Autonomic Control

To summarize, breathing is a potent modulator of cardiovascular and autonomic systems.  Deliberate practice of different breathing patterns (for example, slow breathing) could be beneficial for increasing heart rate variability, improving breathing efficiency, improving chemosensitivity, and enhancing cardio-autonomic control.

Abstract

Respiration is a powerful modulator of heart rate variability, and of baro- and chemoreflex sensitivity. Abnormal respiratory modulation of heart rate is often an early sign of autonomic dysfunction in a number of diseases. In addition, increase in venous return due to respiration may help in maintaining blood pressure during standing in critical situations. This review examines the possibility that manipulation of breathing pattern may provide beneficial effects in terms not only of ventilatory efficiency, but also of cardiovascular and respiratory control in physiologic and pathologic conditions, such as chronic heart failure. This opens a new area of future research in the better management of patients with cardiovascular autonomic dysfunction.

Journal Reference:

L Bernardi, C Porta, A Gabutti, L Spicuzza, P Sleight.  Modulatory Effects of Respiration.  Auton Neurosci. 2001;90(1-2):47-56. doi: 10.1016/S1566-0702(01)00267-3.

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.

Slow breathing improves autonomic function in type 1 diabetics

Key Points

• Slow breathing increased autonomic function, arterial function, and blood oxygen saturation in type 1 diabetic patients

• Slow breathing stimulates the parasympathetic nervous system and suppresses the sympathetic nervous system, providing an antioxidant effect

• “Slow breathing could be a simple beneficial intervention in diabetes.”

Breathing Blueprint Summary

The last key point above, taken directly from the abstract, says it all. This paper was published in Nature, one of the most prestigious scientific journals around, and they are highlighting the usefulness of slow breathing for diabetes and autonomic function in general.  Pretty awesome.

Diabetics suffer from an enhanced risk for cardiovascular disease, which is associated with autonomic dysfunction.  However, slow breathing has been shown to restore autonomic balance, suggesting that it might be applicable in type 1 diabetes.

Participants in the study performed 5 minutes of spontaneous breathing, followed by 2 minutes of slow breathing at 6 breaths/min.  That is a very short amount of time, yet they still got fairly remarkable results. 

During spontaneous breathing, diabetics had worse baseline data than controls.  For example, diabetics had a lower resting blood oxygen saturation and higher blood pressure.  The main marker of autonomic function that they measured was the baroreflex sensitivity (BRS). BRS measures your body’s ability to quickly adjust your blood pressure to match the current circumstances.  At baseline, the diabetics’ had a lower BRS score.

However, after just 2 minutes of slow breathing, their BRS increased to values similar to those of the controls during spontaneous breathing.  The authors believe this occurred due to a reduction in sympathetic nervous system activity and an increase in parasympathetic activity.

They also provide evidence that this shift in autonomic activity has a direct antioxidant effect.  Because diabetics (and really anyone with a chronic disease) suffer from excess oxidative stress and free radicals, this aspect of slow breathing is extremely important for improving our overall health and well-being.

Lastly, slow breathing also improved the arterial function and blood oxygen saturation of the diabetics. The authors suspect the improvements in oxygen saturation were due to improved ventilation perfusion (i.e., better matching of air and blood flow in the lungs). 

In summary, with only 2 minutes of slow breathing, type 1 diabetics were able to improve autonomic function, enhance antioxidant capacity, and improve blood oxygen saturation. These results provide practical evidence that slow breathing can improve the overall health of diabetics.

Abstract from Paper

Hyperoxia and slow breathing acutely improve autonomic function in type-1 diabetes. However, their effects on arterial function may reveal different mechanisms, perhaps potentially useful. To test the effects of oxygen and slow breathing we measured arterial function (augmentation index, pulse wave velocity), baroreflex sensitivity (BRS) and oxygen saturation (SAT), during spontaneous and slow breathing (6 breaths/min), in normoxia and hyperoxia (5 L/min oxygen) in 91 type-1 diabetic and 40 age-matched control participants. During normoxic spontaneous breathing diabetic subjects had lower BRS and SAT, and worse arterial function. Hyperoxia and slow breathing increased BRS and SAT. Hyperoxia increased blood pressure and worsened arterial function. Slow breathing improved arterial function and diastolic blood pressure. Combined administration prevented the hyperoxia-induced arterial pressure and function worsening. Control subjects showed a similar pattern, but with lesser or no statistical significance. Oxygen-driven autonomic improvement could depend on transient arterial stiffening and hypertension (well-known irritative effect of free-radicals on endothelium), inducing reflex increase in BRS. Slow breathing-induced improvement in BRS may result from improved SAT, reduced sympathetic activity and improved vascular function, and/or parasympathetic-driven antioxidant effect. Lower oxidative stress could explain blunted effects in controls. Slow breathing could be a simple beneficial intervention in diabetes.

Journal Reference:

Bernardi L, Gordin D, Bordino M, Rosengård-Bärlund M, Sandelin A, Forsblom C, Per-Henrik Groop PR. Oxygen-induced impairment in arterial function is corrected by slow breathing in patients with type 1 diabetes. Sci Rep. 2017;7:6001. DOI:10.1038/s41598-017-04947-4.