QUESTION: When breathing through the mouth, we exhale more carbon dioxide than the body produces, and your theory is that the respiratory tract in the nose is blocked to prevent excessive carbon dioxide outflow. I have previously read the book Relaxation and Mental Training — For a Richer Lifeby Eva Johansson, and it says this: “It is also important that you breathe out properly.”

Then, an increase in the level of carbon dioxide in the blood is prevented, which in itself can create anxiety. This makes me a bit confused. Have I misunderstood something? If we breathe through the nose, may we get too much carbon dioxide in the blood?

ANSWER: As with everything else, it is all about balance, so we may have too much carbon dioxide, and we may have too little. Excessive levels of carbon dioxide are especially common when you have damaged lung tissue and have been diagnosed with COPD (chronic obstructive pulmonary disease) or pulmonary emphysema. For most other people, however, the opposite is true: that the level of carbon dioxide is too low.

However, many people seem to have misunderstood the importance of carbon dioxide for a body in balance and see it only as a residual product that is produced when nutrients are converted to energy in the cells and that it should leave the body as quickly as possible.

I think this common misconception is one reason why it says what it does in Eva Johansson’s book. My view is that carbon dioxide is as far from a simple residual product as it can possibly be. In a rather healthy person, it is the level of carbon dioxide that controls the rate and volume of the breathing. As you get worse, oxygen levels become more important in triggering the breathing reflex, but in most of us it is the carbon dioxide pressure that controls the breathing.

This fact alone, that carbon dioxide controls our breathing, which is the body’s most important function, should be more than enough to kill the myth that carbon dioxide is dangerous. When firefighters in the United States (I do not know about the situation in Sweden) check to see if a person is still alive, they check neither the pulse nor the oxygen saturation in the blood. They check to see if the exhaled air contains carbon dioxide. If it does, it means the person is still alive. One can, thus, have a non-existent pulse but still be alive.

Normal breathing at rest is 6-12 breaths per minute at about half a liter per breath, which gives a breathing volume of 3-6 liters of air per minute and a carbon dioxide pressure of about 40-45 mmHg.

In the case of impaired breathing, it is common for us to breathe more, 18-25 breaths per minute or more, with a larger volume for each breath that gives a breathing volume of 10-15 liters per minute. When we breathe in this way, we lose carbon dioxide and thereby lower the carbon dioxide pressure to below 40 mmHg. A carbon dioxide pressure of 35 mmHg or lower is considered hyperventilation.

Over time, a new normal state is, thus, established in the body, where the respiratory reflex is triggered by even lower carbon dioxide levels in the blood. When we practice breathing, we teach the body to tolerate a higher carbon dioxide pressure so that the breathing reflex is triggered less frequently.

In addition to controlling breathing, carbon dioxide has many other important functions, including:

• Germicidal agent. It has been used in the food industry since the 1930s, and, for example, cheese and coffee are packed in 100% carbon dioxide.
• Expanding smooth muscles. It has a widening and relaxing effect on smooth muscles, the muscles we cannot control with the will, which are found in respiratory passages, blood vessels, intestines, the uterus, etc.
• Increasing oxygenation. It causes oxygen to be more easily released from blood into our cells to be used for cellular respiration (this is called the Bohr effect).

Here is an article I wrote in an attempt to clarify the topic: “Carbon dioxide pressure is more important than blood pressure“.