Your breathing is shallow and irregular for 1/3 of your life

Key Points

• Breathing volume decreases between 6% and 16% during sleep

• Breathing is shallow and irregular during sleep

• We experience relative hypoxia and hypercapnia during sleep

The Breathing Diabetic Summary

To understand sleep-related breathing disorders, we first have to understand normal breathing during sleep.  That was the goal of this study.

Experiments were conducted with 19 subjects (8 males, 11 females) that had no history of sleep complaints.  Additionally, they were all nocturnal sleepers.  The researchers studied them between 10 PM and 7 AM.  They studied one subject on 3 nights, 9 subjects on 2 nights, and 9 subjects on 1 night.

Baseline measurements were obtained while the patients were lying in bed either before falling asleep or after waking up (using EEG-confirmed wakefulness).  Theses recordings were subsequently averaged to produce the “awake” value. 

For measurements of breathing during different sleep stages, the subjects had to stay in that sleep stage continuously for at least 2 minutes.  Additionally, there could not be any detectable leaks within the breathing mask they were wearing.

Comparison of the awake versus sleeping parameters revealed that breathing volume reduced significantly during sleep.  For non-REM sleep, breathing volume decreased between 6% and 8%.  During REM sleep, ventilation reduced by ~16%.  Interestingly, the breathing rates of these subjects were slightly faster during sleep than while awake, suggesting that breathing becomes shallower during sleep.

Because the participants were breathing less, they became significantly more hypoxic (low O2) and hypercapnic (high CO2) while asleep compared to while awake.

The researchers used this information, along with assumptions regarding lung dead space and dead space due to the breathing mask, to estimate the change in gas exchange occurring in the lungs.  These calculations revealed a reduction in gas exchange between 19% and 39% during sleep, helping explain why the participants experienced hypoxia and hypercapnia.

Lastly, during non-REM sleep, breathing rates were somewhat regular (although a few patients still showed irregular rates during non-REM).  In REM sleep, all participants exhibited shallow and irregular breathing patterns. 

Overall, these results show that breathing volume is reduced during all stages of sleep. The greatest reductions occur during REM sleep, which is also when breathing rate is the most irregular and unstable. The reduction in breathing leads to relative hypoxia and hypercapnia. Interestingly, these breathing patterns are normal and are part of the natural physiological changes our bodies makes during sleep.

Abstract

Respiratory volumes and timing have been measured in 19 healthy adults during wakefulness and sleep. Minute ventilation was significantly less (p less than 0.05) in all stages of sleep than when the subject was awake (7.66 +/- 0.34(SEM) 1/min), the level in rapid-eye-movement (REM) sleep (6.46 +/- 0.29 1/min) being significantly lower than in non-REM sleep (7.18 +/- 0.39 1/min). The breathing pattern during all stages of sleep was significantly more rapid and shallow than during wakefulness, tidal volume in REM sleep being reduced to 73% of the level during wakefulness. Mean inspiratory flow rate (VT/Ti), an index of inspiratory drive, was significantly lower in REM sleep than during wakefulness or non-REM sleep. Thus ventilation falls during sleep, the greatest reduction occurring during REM sleep, when there is a parallel reduction in inspiratory drive. Similar changes in ventilation may contribute to the REM-associated hypoxaemia observed in normal subjects and in patients with chronic obstructive pulmonary disease.

Journal Reference:

Douglas NJ, White DP, Pickett CK, Weil JV, Zwillich CW.  Respiration during sleep in normal man.  Thorax.  1982;37(11):840-844.

Our somewhat unusual breathing patterns during sleep

Key Points

• Breathing volume is reduced by as much as 16% during sleep

• Breathing rate is variable during sleep, especially in REM

• Hypoxic and hypercapnic responses are reduced by as much as 66% during sleep

The Breathing Diabetic Summary

We spend approximately 1/3 of our life sleeping.  And although sleep science is still relatively new, it’s undeniable that sleep is a key component of achieving optimal health.  Which begs the question, if sleep is so restorative, what is happening to our breath during this time?

Published in 1984, this review study found that breathing is significantly reduced during all stages of sleep.  This reduction can be as great as 16%.

Somewhat surprisingly, our breathing rate is extremely variable during sleep.  I expected that our breathing would become rhythmic and deep.  However, research shows that the opposite is true.  We breathe shallower and our breathing rate remains the same, or even increases slightly.

Additionally, it differs for different stages of sleep.  During non rapid eye movement sleep (non-REM), our breathing volume reduces and we sometimes achieve a steady rhythm.  In REM sleep, however, our breathing volume reduces even more, but our rate becomes more sporadic.

We also experience relative hypoxia (low O2) and hypercapnia (high CO2).  In fact, our tolerance to CO2 increases dramatically.  One study suggested that during non-REM, CO2 tolerance increases by ~33%.  During REM sleep, it increases by about 66%.  That’s fairly remarkable.

So, to summarize, here is what happens to breathing during sleep:

• Breathing volume reduces

• Breathing rate is variable

• Hypoxic and hypercapnic responses are reduced

The processes occurring during sleep clearly serve a purpose in restoring health.  If we interrupt these processes, we will not harness the full power of sleeping.

Therefore, if you are breathing with an open mouth during sleep, you are probably breathing too much and not supporting restorative sleep.Luckily, it’s an easy fix.Simply taping your mouth at night is the first step toward achieving optimal breathing volumes during sleep.

Journal Reference:

Douglas NJ.  Control of Breathing during Sleep.  Clin Sci (Lond).  1984;67(5):465-471.

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.