For most people breathing is seen just as an exchange of air —oxygen is inhaled, and CO2 is exhaled. Like so many analogies, this is only partially true and I actually believe that it conflates the process and mechanics enabling breathing with the act itself. Further, it also perpetuates the common misunderstanding that CO2 is merely a harmful "waste product".

According to a more pedantic definition I have recently found, breathing, or rather respiration, is the process of burning nutrient fuel within the mitochondria inside the cell, with oxygen acting as a catalyst, to release energy and sustain life.

The Bohr effect (named after the Danish scientists who discovered it) highlights the critical role of CO2 in this process: Oxygen in the atmosphere moves from the nose or mouth down the trachea, through the bronchial system, and into the alveoli, where it is absorbed into the bloodstream, then transferred to the cells, and to it's final destination —the mitochondria—where it is used as catalyst for energy production. CO2 is instrumental for breaking the strong bond between the oxygen molecules and hemoglobin (the red blood cells) allowing oxygen to be released and absorbed by the cells for energy production. Without adequate levels of CO2, this last step cannot happen optimally.

Another scientist who understood the importance of CO2 for health is the Russian Doctor Vladimir Buteyko. Dr Buteyko developed a breathing protocol designed to improve CO2 tolerance, helping individuals successfully manage asthma and many other chronic diseases. To understand the effectiveness of the Buteyko breathing method against asthma, I highly recommend you watch this 30-min BBC documentary (it's from a time when the profession of journalism still meant something.) https://www.youtube.com/watch?v=vtb65UQ3E1c

I'll conclude with this easy exercise to help you measure your CO2 tolerance, it's called the "controlled pause" (or bolt score). Ideally, you want to do it in the morning, just after waking up. (You don't need to do it daily, but the more data you collect, the better.)

PS: I've been tracking and working on mine since last summer. My increased work load since the beginning of the year has affected it, as you can notice. Nevertheless, I trust I have all the tools to improve it whenever needed.