In January, we gave you advice on what affects your air consumption and what you can do to lower it. Today we will go into detail on how breathing works and what you shouldn’t do to improve your air consumption.
Why do we breathe in the first place?
Let us explore why we breathe at all. The air around us is made up of 78.09% Nitrogen (N2), 20.95% Oxygen (O2) as well as 0.93% Argon (Ar). The remaining 0.03% are other noble gases and Carbon dioxide. For diving purposes the main contents of air are Nitrogen and Oxygen. It would be absolutely false to claim that we do not need Nitrogen, as amino acids all contain nitrogen. For our following thoughts we can disregard the Nitrogen though. Oxygen is very reactive with a variety of other elements by forming oxides. This makes it a prime element to extract energy.
However, Oxygen is not the sole reason for our respiratory system. In addition to extracting O2 from the air with every breath, we also rid our body of Carbon dioxide (CO2) with every exhalation. CO2 is a waste product of our body and the way it's produced is rather complex. In a nutshell, our cells use the O2 to release energy and the product gets bound to carbon which results in the waste product CO2.
Our initial thought might be that our body gets us to inhale when our O2 levels are getting low. If this were true, we would actually need to breathe very little. As you have learned during your very first minutes of your Open Water Course, the pressure at depth increases drastically. This in turn increases the partial pressure of all gases, including Oxygen. You might remember that breathing air at 10 metre of depth has the same effect as breathing around 40% of oxygen at the surface. If I descend to 40 metres of depth, the effect of Oxygen is the same as 100% at the surface. The mixture of air in our tank doesn't change, but with every breath we are taking more atoms in than we did at the surface due to an increase in density. In reality we are quite inefficient in extracting O2 from air and with every breath you exhale a good 16% to 17% O2.
Our body does not use O2 to control the respiratory system but rather CO2. When you hold your breath, CO2 levels in your lungs steadily rise, a state called hypercapnia. The higher the level of CO2, the stronger the urge to breathe. At one point we just can’t hold our breath anymore. CO2 is created when our body needs energy. Therefore, the level of CO2 will be at its highest when we either exercise or we fail to effectively remove the accumulated CO2 from our lungs.
Get rid of your carbon dioxide
We have heard countless of times that people want to breathe slower or even skip a breath to improve their air consumption when diving. However, these attempts to conserve air are flawed by design and range from doing nothing to being outright dangerous. One thing that we see more than we would like to is people skipping a breath, called skip-breathing in the dive community. Oxygen demands are easily met using this technique as increased partial pressure delivers more Oxygen atoms with every breath taken. The problem with skipping a breath is CO2 retention. The respiratory system has to be able to expel the created Carbon dioxide and by skipping every other breath it is not able to do so. The result is called hypercapnia, an excess of Carbon dioxide. First signs and symptoms of hypercapnia include muscle twitches, headache, confusion and they can progress to convulsions, unconsciousness and eventually death. In a diving environment the latter are unlikely but a strong headache is quite often the case.
Breathing very shallow but faster has the same effect as the above skip-breathing. You will not allow your body to flush CO2 from its system.
Perfect breathing rhythm
If you ask yourself what the perfect breathing rhythm would look like I have good news for you. Go to your couch, relax and pay attention to what your body is doing. In this state it is most effective at breathing very little air, around 500 mL, but still removing the unnecessary CO2. In this state you are not breathing artificially deep, nor artificially slow. Remember that your body is lazy and will always try to do as little as possible and in that couch scenario you are breathing as little as possible. As little as necessary is exactly what we want to decrease our air consumption.
I know that this is not the answer you came here to find but the simple reply to the question how should I breathe underwater is: Breathe like you do on your couch while watching TV and munching a whole pizza. If you dive in a current it will be a whole different story of course...