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.

Intermittent hypoxia is beneficial in sedentary, non-athletic, and clinical populations

Key Points

• Intermittent hypoxia improves cardio-autonomic function and exercise tolerance

• There are several ways to achieve intermittent hypoxia and receive benefits, including prolonged hypoxic exposure, intermittent hypoxic exposure, and intermittent hypoxic training

• Intermittent hypoxia is beneficial in sedentary and clinical populations

The Breathing Diabetic Summary

I love review papers because they summarize the key findings from the scientific literature in an easy to follow manner. Therefore, anytime I find a review study on a subject of interest, I dive right in.

This one was unique because it looked at the effects of simulated altitude on non-athletic, sedentary, and clinical populations. Most studies on simulated altitude involve elite performers, so it was interesting seeing a review paper focusing on more “everyday” people.

Using different search criteria, they identified 26 studies that have looked at intermittent hypoxia in the abovementioned populations. Within those 26 studies, they then identified 3 different methods of achieving intermittent hypoxia:

1. Prolonged hypoxic exposure (PHE): Continuous hypoxic interval, such as “live high, train low”.

2. Intermittent hypoxic exposure (IHE): Short intervals (5-10 min) of hypoxic:normoxic exposure.

3. Intermittent hypoxic training (IHT): Exercising in hypoxia.

For our purposes, IHE and IHT are the only practical methods for achieving hypoxia via breath holds. However, the results for PHE will also be included for completeness (and, maybe one day altitude tents will be affordable!).

Here, I’ll summarize the benefits they found for each method of hypoxia.

IHE:

• Reduced systemic stress

• Improved heart rate variability

• Improved autonomic balance

• Reduced blood pressure

• Greater exercise tolerance

• Longer time to exhaustion while exercising

• Hematological results were mixed. Some studies showed increased red blood cells, others didn’t.

PHE:

• Improved lung ventilation

• Improved submaximal exercise performance

• Improved blood lipid profile

• Improved blood flow to the heart

IHT:

• Increased aerobic capacity

• Increased fat burning

• Increased mitochondrial density

• Improved autonomic balance

With respect to PHE, the research suggested that at least 1 hour of 12% O2 for 2 weeks would provide the greatest benefits without side effects. They did not provide recommendations for IHE or IHT.

However, a 2014 review study showed that 3-15 episodes of 9-16% O2 is the therapeutic range for IHE. This corresponds to blood O2 saturations of approximately 82-95%.

Also, from a practical perspective, we know that we can perform walking breath holds to achieve mild IHT. Essentially, we combine the IHE protocol with walking.

Overall, this paper suggests that intermittent hypoxia has many benefits in sedentary, non-athletic, and clinical populations, including improved cardiovascular and autonomic function and increased exercise capacity.

It also showed that there are several ways to achieve those benefits: Prolonged exposure, intermittent exposure, or exposure during exercise.

I recommend that you find a modality that fits you or your client’s lifestyle that can be practiced consistently.

Abstract from Paper

BACKGROUND: The reportedly beneficial improvements in an athlete's physical performance following altitude training may have merit for individuals struggling to meet physical activity guidelines.

AIM: To review the effectiveness of simulated altitude training methodologies at improving cardiovascular health in sedentary and clinical cohorts.

METHODS: Articles were selected from Science Direct, PubMed, and Google Scholar databases using a combination of the following search terms anywhere in the article: "intermittent hypoxia," "intermittent hypoxic," "normobaric hypoxia," or "altitude," and a participant descriptor including the following: "sedentary," "untrained," or "inactive."

RESULTS: 1015 articles were returned, of which 26 studies were accepted (4 clinical cohorts, 22 studies used sedentary participants). Simulated altitude methodologies included prolonged hypoxic exposure (PHE: continuous hypoxic interval), intermittent hypoxic exposure (IHE: 5-10 minutes hypoxic:normoxic intervals), and intermittent hypoxic training (IHT: exercising in hypoxia).

CONCLUSIONS: In a clinical cohort, PHE for 3-4 hours at 2700-4200 m for 2-3 weeks may improve blood lipid profile, myocardial perfusion, and exercise capacity, while 3 weeks of IHE treatment may improve baroreflex sensitivity and heart rate variability. In the sedentary population, IHE was most likely to improve submaximal exercise tolerance, time to exhaustion, and heart rate variability. Hematological adaptations were unclear. Typically, a 4-week intervention of 1-hour-long PHE intervals 5 days a week, at a fraction of inspired oxygen (FIO2) of 0.15, was beneficial for pulmonary ventilation, submaximal exercise, and maximum oxygen consumption ([Formula: see text]O2max), but an FIO2 of 0.12 reduced hyperemic response and antioxidative capacity. While IHT may be beneficial for increased lipid metabolism in the short term, it is unlikely to confer any additional advantage over normoxic exercise over the long term. IHT may improve vascular health and autonomic balance.

Journal Reference:

Lizamore CA, Hamlin MJ.  The Use of Simulated Altitude Techniques for Beneficial Cardiovascular Health Outcomes in Nonathletic, Sedentary, and Clinical Populations: A Literature Review.  High Alt Med Biol.  2017;18(4):305-321.