Let’s start with understanding why we (as humans) breathing. Yes, we all know that we need O2 (oxygen) for our life and this is one of the main functions of our respiratory system – bring O2 to our tissues.
But do you know that our breathing rate is mainly regulated by the amount of CO2 (partial pressure of CO2) in the blood, not O2. We even have a specific part of our brain responsible for this regulation. It has a very difficult name – Medulla Oblongata. This “thing” is responsible for such automatic functions as breathing, heart and blood vessels function, swallowing, digestion.
Why is it important to know, especially for beginner Freedivers?
Well, we all know that some of our tissues couldn’t operate without O2 even a short amount of time. For example – our brain. And when beginners hold their breath and feel the desire to breathe, they start to be nervous because they are thinking the level of O2 critically low! And it is becoming dangerous!
And – if not, why they feel uncomfortable?
Let’s say you are holding your breath for a minute.
Even if you are relaxed as much as possible, you still produce some energy. And as a result, produce some CO2. And when your CO2 reaches a certain level you want to breathe (actually you want to remove excess CO2 level). In Freediving quite often we use the term “urge to breathe”. So, how are going to bring new air to your lungs? What is the process looks like?
Our main respiratory muscle is our diaphragm. It is a big muscle between your chest (thoracic) cavity and abdominal cavity. When you need to inhale – your diaphragm going down (contraction of the diaphragm), chest volume increase and the air suck in. Reverse process happens when you exhale – you relax your diaphragm and it is coming to its normal position, pushing the air out of your lungs. Intercostal muscles (muscles between your ribs) involved as well, helping you make a bigger inhale or exhale.
And now let’s come back to urge to breath. When you are holding your breath and have an urge to breathe – it is simple contractions of your respiratory muscles (diaphragm for example), which are trying to remove CO2 from your body.
As a beginner, you want to stop holding your breath after you have a contraction, or a few seconds later (5-15 is a good start). But with the practice, you can hold your contractions much longer. And let me remind you, that contractions are not connected with the level of O2, it is a simple response of your respiratory system for a high level of CO2. So, you are safe when you have them, don’t be scared.
But what exactly happens with the air, when it comes to our lungs? You inhale fresh air (only 21% is O2, 78,96% N and 0.04 is CO2) and it starts its journey into your circulatory system! There is a natural dead space (no one dies, there is just no gas exchange) on its way (nose/mouth + trachea + bronchi + bronchial), so when air reach your alveoli, it has less O2 than you when you inhale.
Your alveoli are tiny compartments where gas exchange happens between your lungs and your blood (capillaries). The wall of alveoli is thin enough for gas (gas traveling both directions, from alveoli to blood vessels and back) and not thin enough for liquid (this is why blood normally couldn’t penetrate into your respiratory system).
So, from alveoli, O2 moves into your blood, where most of it binds with the hemoglobin and use it as a taxi to get to different tissues (your muscles for example) through arteries.
And within your tissues, cells use O2 for producing energy and also creating CO2 as a byproduct (as well as water). After CO2 produced, it goes to your blood (partially connected with hemoglobin, but mostly dissolved into the plasma – bicarbonate) and then going through veins to your lungs. Then again, through gas exchange, CO2 penetrates to your alveoli, going all the way up to your mouth and then you remove it through exhaling! This how we are breathing!
Pretty simple, right?
A few words about the importance of CO2 in our body.
If CO2 is just a byproduct of producing energy and our “urge to breath” depends on it, might be we need to remove it from our system before a breath hold activity? And then can stay underwater longer?
Probably same thought had freediving pioneers when they were doing hyperventilation (which is a big no-no nowadays). Basically, hyperventilation (or over breathing) is the process when you ventilate your lungs too fast.
What happens when you do hyperventilation – you reduce the level of CO2 in your body, which cause increasing pH of your blood (blood become more alkaline – respiratory alkalosis) and it triggers Bohr effect – now a connection between hemoglobin and O2 becomes stronger and exchange between capillaries and tissues becomes harder. In simple words – even if enough O2 present in the blood, it is much harder to deliver it to tissues. Since the human brain is very sensitive to the lack of O2, as a result of hyperventilation we have symptoms – dizziness, tingling in the lips, hands or feet, headache, weakness. Or in a worst case scenario – unconsciousness (our brain simple protect us from further depleting of O2).
So, CO2 playing an important part in keeping pH of our blood constant (7.34-7.45), so-called acid-base homeostasis
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