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This article is going to discuss the physiological aspects of breathing, specifically related to our primary blood gases, oxygen (O2) and carbon dioxide (CO2). “The Oxygen Advantage” by Patrick Mckweon and “Advanced Buteyko Breathing Exercises” by Artour Rakhimov serve as the primary resources for this article and where you may obtain more information on this topic.

The primary purpose of breathing is to take in oxygen, one of our most vital nutrients. About 90% of our energy production requires O2 and thus impacts virtually every cellular, tissue, and systemic process in our body. A by-product of these cellular energy reactions is CO2 and thus is generally considered a waste product.

Typically, we assume that we need to take big breaths to maximize O2 and minimize CO2 levels in our body. In reality, we don’t need to take bigger breaths or breathe more frequently to increase our O2 blood saturation as it takes very little breath volume and rate to do so. The key element is getting O2 to disassociate from our red blood cells (hemoglobin) and get into our tissues.

The trigger to facilitate O2 to leave hemoglobin and get into our cells is actually CO2!

Yes, we need adequate levels of CO2 in our blood to serve as a stimulus for O2 to transfer into our cells, tissues, and organs. CO2 is not just a “waste product” for us to excrete via exhalation but a potent driver of our ability to fully oxygenate our body!

What determines our level of CO2 in our blood? How much we breathe! If one is over-breathing they are likely getting rid of too much CO2 for adequate oxygenation. Over-breathing can be characterized by taking too big of a breath and/or breathing too rapidly. For example, fast breathing is very commonly seen in asthmatics. In fact, Buteyko breathing techniques (as will be described here) have been heavily used in asthmatics with amazing success. However, the problem of over-breathing is not limited to asthmatics but has become a modernized society health issue as most of us are not breathing correctly. This even includes elite level athletes!

We generally aim for our patients to achieve about 8-10 breaths/minute but we typically find that many of our patients are averaging significantly more than this. On the flipside, some individuals will have a slower breath rate but are taking too big of a breath coupled with excessive belly breathing. Please refer to this video to learn more about belly breathing:

Regardless of whether you are breathing too rapidly or with too much volume per breath, either scenario is considered chronic hyperventilation and is taking away too much CO2 out of the lungs and blood.

One breathing pattern that lends itself to chronic hyperventilation is habitual mouth breathing which results in a higher volume breathing averaging 12-15 L/min compared to nasal breathing which is ~ 6 L/min. Therefore, if you mouth breathe you are nearly doubling your air volume with excessive CO2 loss!

Once these blood gas “habits” are established the nervous system adjusts and establishes a baseline point where it aims keep the same CO2 level. The nervous system perceives this to be a “safe” level and is constantly modifying your breath rate and volume to stay within this range. Therefore, if one starts to increase one’s CO2 levels by either reducing their breathing rate and/or volume they may feel like they aren’t getting enough air. We refer to this as “air hunger” as it makes one feel a bit panicky. This is the nervous system’s way of trying to protect you and thus what keeps one ultimately in an over-breathing pattern.

We can determine the extent of our CO2 tolerance/set-point with the following test, which we refer to as the “control pause” or the “BOLT” (Body Oxygen Level Test) based off of the Buteyko Breathing method. To perform the test:

  1. After a regular exhale, pinch your nose to hold your breath and start a stopwatch.
    • Note-do not take a bigger breath in or out prior to starting the test.
  2. Hold your breath until you feel a moderate urge to breathe.
    • Note-this is not testing how long you can maximally hold your breath, just until the first urge.
  3. At this point stop the clock. The time recorded is your score.
    • A time of 40 sec or more is considered excellent, 30-40 good, 20-30 fair, and below 20 poor. It has been found that there is a correlation between these scores and overall health with decreasing health the lower the score, particularly below 10 sec.

Now for the most important part: How do we improve our breathing so we can get enough oxygen delivery to our body?

First, if you are habitually mouth breathing you need to switch to nasal breathing. In addition to facilitating an appropriate breathing volume, nasal breathing has a number of other important physiological effects on the body. Nasal breathing warms and humidifies air for improved gas exchange vs mouth breathing which can be very dehydrating. It is via airflow through the nasal cavity which promotes nitric oxide (NO) production. NO is a powerful anti-microbial agent and serves to sanitize the air we breathe. This can also impact the type of microbiome colonies in the oral cavity and gut which is extremely important for our health. NO is a vasodilator which has implications for improving gas exchange in the lungs as well as influencing circulation and blood pressure.

In addition to learning how to breathe through your nose during the day it is imperative that you only nasal breathe when you sleep. If you continue to mouth breathe during sleep you will essentially reverse all the good training you did during the day as well as reduce your body’s ability to oxygenate. This is crucial for the cellular repair that should be occurring during sleep. A simple, inexpensive solution to ensure consistent nasal breathing during sleep is to tape the lips. I recommend using the hypoallergenic tape, Hypafix, (can easily be bought on Amazon) that can be cut into strips to be placed over the lips as displayed below. Myself, husband, father, and many of my patients are proud mouth tapers!

If you are unable to consistently breathe through your nose then that must be addressed first. There can be a myriad of reasons why this is a problem as well as solutions which is not within the scope of this article. However, if you are limited with nasal airflow one thing you may try is a nasal clearing technique described by Patrick McKweon here:

“Reduced Breathing Training,” which is a version of Butekyo breathing has been shown to significantly improve one’s CO2 tolerance. It must be done for a minimum of 5 min, 2x day to have a significant carry-over effect but we have many patients practice up to 30-60 min a day broken up into segments no less than 4-5 minutes at a time. The first step is to take notice of your habitual breathing pattern. How many breaths do you take a minute?  Is there is any pause between the exhale and inhale? Do you take big or small breaths?

To begin the training, using a soft and gentle breath size (which is what your habitual breath quality should be) pause an extra 1-3 seconds after each EXHALE. You are essentially trying to slow down and soften your breathing rate and overall air volume which will gently increase the levels of CO2 in your lungs and blood. This will create a level of “air hunger” and discomfort. It is very important that you keep the intensity of this “air hunger” to no more than minimal. You will likely need to adjust the amount of time you are pausing after each exhale to maintain this mild intensity of air hunger while training. If you push beyond the minimal limit your nervous system will perceive you are in a stressful state and try to protect you by not allowing it to learn a new set point. This amount of time will vary from person to person as well as for a person depending on the time of day, recent food/beverage consumption, room temperature, activity level, etc. After you have practiced this for 5 min go back to your normal breathing pattern for 60 sec and then retest your control pause. It should have increased. If it didn’t or went down then you most likely pushed yourself too hard during the training and need to adjust.

Progress will vary from person to person but generally one should aim for their control pause to improve a few seconds each week. To get a more accurate and consistent control pause, it is recommended to take it every morning when one first awakes. When one’s control pause gets into the 20s there are also walking and exercise breathing techniques that can be incorporated to further progress. Overall, when one is performing exercise the goal is to only breathe through the nose. A great way to work up to this is to aim to maintain nasal breathing during walking and regular day to day activity in addition to at rest.

It is important to point out that certain individuals may need to proceed very cautiously or seek training from an experienced practitioner. Examples are individuals with heart or lung disease, migraines, post-concussion syndrome, any acute trauma, chronic infections, dysautonomia conditions such as POTs, or if you feel worse after trying the technique. If you are not making progress despite keeping yourself within the mild training parameters, there may be other factors that need to be addressed such as environmental problems. Examples are living or working in an environment with toxins such as dust, mold, poor ventilation, too high of a temperature (particularly during sleep), and/or consuming too may processed foods.

Finally, this article describes the physiology related to breathing. However, as mentioned in a prior post (, it is also just as important to breathe properly from a biomechanical and postural perspective. In fact, these two aspects are inter-connected with one another. It will be very difficult to maintain appropriate breathing physiology if you are not properly breathing with your diaphragm and vice versa.

By Heather Carr, DPT

Founder of One 2 One Physical Therapy