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.

Meta-Analysis: Slow Breathing Reduces Systolic Blood Pressure by 5.62 mmHg

Key Points

• Diabetics are at an increased risk of hypertension and its negative cardiovascular outcomes

• Slow breathing reduces systolic blood pressure by 5.62 mmHg and diastolic blood pressure by 2.67 mmHg

• Slow breathing is a simple way to reduce blood pressure and potentially improve cardiovascular outcomes

The Breathing Diabetic Summary

Hypertension is a significant risk factor for cardiovascular disease, which is the leading cause of death in the U.S. For instance, if systolic blood pressure rises from 115 mmHg to 135 mmHg, your risk of cardiovascular disease doubles.

People with diabetes are also much more likely to develop hypertension. Anywhere from 40 to 80% of diabetics have hypertension, a somewhat somber statistic. Moreover, I am writing this in April 2020 during the COVID-19 pandemic. Studies are revealing that hypertension is correlated with more severe complications.

All of this is to say that reducing blood pressure is more important than ever. There are several medications and lifestyle changes available; however, compliance with these approaches are often low. Therefore, alternative therapies are needed. One such treatment is slow breathing.

Slow Breathing and Hypertension

Slow breathing has consistently been shown to reduce blood pressure. In particular, a device called RESPeRATE (which is FDA approved), which slowly reduces breathing rate down to below ten breaths per minute, has been examined extensively. The American Heart Association has even given device-guided slow breathing a “class IIA” rating for reducing blood pressure.  

This meta-analysis provides a concise yet comprehensive summary of studies that have examined slow breathing and hypertension. Their strict search criteria and thorough review of the available randomized controlled trials (RCTs) make this the most robust meta-analysis of slow breathing and blood pressure published to date. 

Study Inclusion and Strict Search Criteria

The authors searched several public databases (e.g., Web of Science, MEDLINE) since their inception until mid-2015. They used a combination of search terms like “hypertension OR prehypertension” and “slow breathing OR device-guided breathing” to identify papers relevant to the meta-analysis.

In the identified papers, slow breathing was defined as anything below ten breaths per minute. The subjects had to perform slow breathing at least three times a week for at least 5 minutes each session. They included studies of people with both hypertension and prehypertension. The follow-up period had to be at least 4 weeks and changes in blood pressure had to be reported. They excluded studies of healthy subjects without baseline hypertension or prehypertension

Selecting Relevant Studies and Publication Bias

The authors started with 1,984 studies, but only 17 met their criteria for inclusion in the meta-analysis. Although meta-analyses are some of my favorites, there are caveats that we need to mention for this one.

Of the 17 studies selected, five were abstracts only. Additionally, only two had slow breathing without a device. The other fifteen were device-guided slow breathing using the RESPeRATE, and the maker of the device sponsored six of these. Thus, there was a high risk of publication bias with these studies.

Slow Breathing Significantly Reduces Blood Pressure

Despite these limitations, the collective results were impressive. The average decrease in systolic blood pressure (SBP) across all seventeen studies was 5.62 mmHg. The two non-device slow breathing studies had an even more significant drop of 7.69 mmHg. For diastolic blood pressure, the mean decrease was 2.67 mmHg for the device-guided slow breathing.  

Longer Practice Leads to Better Results

They also examined how the intensity of the slow breathing practice affected results—the conclusion: the longer subjects practiced, the greater their reduction in blood pressure. For example, for slow breathing <100 min a week, the decrease in SBP was 3.01 mmHg, for 100-200 min, it was 6.44 mmHg, and for >200 min, it was 14.00 mmHg.  

Reduced Blood Pressure Reduces Risk of Death

The significance of these findings is that modest reductions in blood pressure lower the chances of strokes, coronary events, heart failure, cardiovascular deaths, and total deaths. This is especially important for diabetics who are at higher risk of developing hypertension and heart disease.

Moreover, the improvements from slow breathing were similar to those seen with antihypertensive medications. Those medications have been shown to improve long-term outcomes in hypertensive and prehypertensive patients. Therefore, slow breathing could potentially provide similar positive results if practiced consistently over a long period.

Slow Breathing is Free and Has No Side Effects

Finally, slow breathing is free, easy to perform, and does not have any side effects. Moreover, the blood-pressure-lowering effects of slow breathing are far-reaching. For example, slow breathing helps with stress, anxiety, and depression, all of which will also help reduce blood pressure.

A Recap of the Main Points 

In summary, slow breathing reduces systolic blood pressure by 5.62 mmHg and diastolic blood pressure by 2.67 mmHg. The more time you practice per week, the greater the blood pressure reductions.  Slow breathing also lowers blood pressure by helping with anxiety, stress, and depression. And by lowering your blood pressure, you reduce the risk of many cardiovascular problems, like stroke or heart disease.

To begin, try breathing at six breaths per minute (4 sec inhale, 6 sec exhale) for five minutes a day and see how you feel. 

Abstract

OBJECTIVES: Interest is increasing in nonpharmacological interventions to treat blood pressure in hypertensive and prehypertensive patients at low cardiac risk. This meta-analysis of randomized controlled trials assesses the impact of device-guided and non-device-guided (pranayama) slow breathing on blood pressure reduction in these patient populations.

METHODS: We searched PubMed, EMBASE, CINAHL, Cochrane CENTRAL, Cochrane Database of Systematic Reviews, Web of Science, BIOSIS (Biological Abstracts) Citation Index and Alt HealthWatch for studies meeting these inclusion criteria: randomized controlled trial or first phase of a randomized cross-over study; subjects with hypertension, prehypertension or on antihypertensive medication; intervention consisting of slow breathing at ≤10 breaths/minute for ≥5 min on ≥3 days/week; total intervention duration of ≥4 weeks; follow-up for ≥4 weeks; and a control group. Data were extracted by two authors independently, the Cochrane Risk of Bias Tool assessed bias risk, and data were pooled using the DerSimonian and Laird random effects model. Main outcomes included changes in systolic (SBP) and/or diastolic blood pressure (DBP), heart rate (HR), and/or decreased antihypertensive medication.

RESULTS: Of 103 citations eligible for full-text review, 17 studies were included in the meta-analysis. Overall, slow breathing decreased SBP by -5.62 mmHg [-7.86, -3.38] and DBP by -2.97 mmHg [-4.28, -1.66]. Heterogeneity was high for all analyses.

CONCLUSIONS: Slow breathing showed a modest reduction in blood pressure. It may be a reasonable first treatment for low-risk hypertensive and prehypertensive patients who are reluctant to start medication.

Journal Reference:

Chaddha A, Modaff D, Hooper-Lane C, Feldstein DA.  Device and non-device-guided slow breathing to reduce blood pressure: A systematic review and meta-analysis.  Complement Ther Med. 2019;45:179-184. doi: 10.1016/j.ctim.2019.03.005.

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.

Hypoxia has positive impacts on insulin and blood glucose levels while also increasing energy expenditure

Key Points

• Hypoxia positively impacts insulin and blood glucose while also increasing energy use

• Hypoxia and exercise combined reduce weight and blood pressure in obese patients

• The positive effects of hypoxia are dose-dependent

Breathing Blueprint Summary

I love review studies because they save us a lot of time.  Researchers go through all of the literature on a specific topic and consolidate everything into one place for us to read. I like to think of The Breathing Diabetic as a big review of all of the research on breathing, health, and well-being…

This paper reviewed the literature on the potential therapeutic benefits of hypoxia for obese individuals.  We know from other papers we have reviewed on hypoxia that there are many benefits for diabetics as well.  And, since diabetes and obesity often occur simultaneously, this review study is relevant for us.

One important point they make, which bears repeating, is that it is not feasible for us all to have access to high altitude.  We cannot simply move to the mountains, or somewhere close enough, to periodically expose ourselves to high altitude.  But, there are ways to experience some of the effects of altitude while at sea level.  The authors specifically mention masks and tents that can reduce the amount of inspired oxygen to simulate high altitude.  However, we cannot forget that breath holds also simulate high altitude and are available to us anytime, for free!

One of the key findings was that fasting blood glucose and insulin levels were reduced in animals following intermittent hypoxia.  Additionally, energy expenditure was increased in animals following hypoxic exposure.  Finally, hypoxia combined with exercise (what they called “active hypoxia”) decreased body weight and blood pressure in obese humans.

They also found contradictory results in some studies, which appeared to be due to the severity of the hypoxia protocol used (something we have reviewed previously). Thus, again we see that the benefits of hypoxia are dose-dependent.

Overall, the authors conclude that hypoxia could be beneficial for obese populations. However, the improvements in insulin, blood glucose, weight, and blood pressure shown here are further evidence that intermittent hypoxia (Principle 3) can benefit anyone looking to improve overall health and well-being.

Abstract From Paper

Normobaric hypoxic conditioning (HC) is defined as exposure to systemic and/or local hypoxia at rest (passive) or combined with exercise training (active). HC has been previously used by healthy and athletic populations to enhance their physical capacity and improve performance in the lead up to competition. Recently, HC has also been applied acutely (single exposure) and chronically (repeated exposure over several weeks) to overweight and obese populations with the intention of managing and potentially increasing cardio-metabolic health and weight loss. At present, it is unclear what the cardio-metabolic health and weight loss responses of obese populations are in response to passive and active HC. Exploration of potential benefits of exposure to both passive and active HC may provide pivotal findings for improving health and well being in these individuals. A systematic literature search for articles published between 2000 and 2017 was carried out. Studies investigating the effects of normobaric HC as a novel therapeutic approach to elicit improvements in the cardio-metabolic health and weight loss of obese populations were included. Studies investigated passive (n = 7; 5 animals, 2 humans), active (n = 4; all humans) and a combination of passive and active (n = 4; 3 animals, 1 human) HC to an inspired oxygen fraction (FIO2) between 4.8 and 15.0%, ranging between a single session and daily sessions per week, lasting from 5 days up to 8 mo. Passive HC led to reduced insulin concentrations (-37 to -22%) in obese animals and increased energy expenditure (+12 to +16%) in obese humans, whereas active HC lead to reductions in body weight (-4 to -2%) in obese animals and humans, and blood pressure (-8 to -3%) in obese humans compared with a matched workload in normoxic conditions. Inconclusive findings, however, exist in determining the impact of acute and chronic HC on markers such as triglycerides, cholesterol levels, and fitness capacity. Importantly, most of the studies that included animal models involved exposure to severe levels of hypoxia (FIO2 = 5.0%; simulated altitude >10,000 m) that are not suitable for human populations. Overall, normobaric HC demonstrated observable positive findings in relation to insulin and energy expenditure (passive), and body weight and blood pressure (active), which may improve the cardio-metabolic health and body weight management of obese populations. However, further evidence on responses of circulating biomarkers to both passive and active HC in humans is warranted.

Journal Reference:

Hobbins L, Hunter S, Gaoua N, Girard O. Normobaric hypoxic conditioning to maximize weight loss and ameliorate cardio-metabolic health in obese populations: a systematic review. Am J Physiol Regul Integr Comp Physiol. 2017;313:R251-R264.