Over the last couple of months, I have noticed that even some Freediving professionals do not entirely understand how breathing control in freedivers works. And be honest, while I was writing this article, I found out that I was not 100% correct either.
Hopefully, this post helps you to understand better what exactly happens with your respiratory system when you hold your breath. And if you find any mistake here, feel free to correct me – I am still learning as well!
At Kaizen Freediving, we teach breathing control on our Freediving courses, but here I put more details about the topic.
To understand better breathing control for Freedivers, we start with the basics. We have two types of chemoreceptors, which detect chemical changes in our body and send signals to the respiratory centre. From the respiratory centre, impulses are sent to our external intercostal muscles and diaphragm, to change the volume and frequency of our breathing (or cause “urge to breathe” if you are holding your breath).
We can divide these receptors into two categories
1. CENTRAL CHEMORECEPTORS
Why “central”? These receptors are part of our central nervous system and the brain (located inside the Pons and the Medulla Oblongata). Since these receptors are not inside blood vessels, they respond to high CO2/H+ not within the blood, but within cerebrospinal fluid (CSF), which is separated from the blood vessels by the blood-brain barrier (BBB).
Let’s make an example. A freediver holds his breath for a few minutes. As the amount of CO2 increases in his blood, the amount of H+ also increases, creating a low pH (respiratory acidosis). H+ doesn’t diffuse through the BBB, but CO2 does. This CO2 bonds with water inside the CSF and produces H+, an increased amount of which is detected by central chemoreceptors.
CO2+H20↔H2CO3↔HCO3+H+
The level of lactate has an impact on this process as well. Lactate, produced during anaerobic energy production, in the form of lactic acid, can cross the BBB, where it breaks down into lactate and H+, eventually leading to the activation of central chemoreceptors.
Eventually, central chemoreceptors can desensitise, which is why we have the potential to become less sensitive to high H+ over a period of training with exposure to a high CO2 (whether it is a CO2 tolerance training or some form of high-intensity interval training).
2. PERIPHERAL CHEMORECEPTORS
They are not part of the central nervous system (instead, they are an extension of the peripheral nervous system) and are located inside the aorta (the largest artery of the human body). More specifically, inside the aortic and carotid bodies. Interesting fact – here we have one of the highest blood flows in the human body.
Chemoreceptors inside the aortic body are sensitive to the change of partial pressure of CO2 and O2. If there is a change, they send the signal to the Medulla Oblangata via the Vagus nerve.
Chemoreceptors inside the carotid body are sensitive to changes in the partial pressure of CO2/O2 and changes in pH (metabolic changes, due to high lactate production, for example). And if there is a significant change, send the signal to the respiratory centre via the Glossopharyngeal nerve.
The main function of peripheral chemoreceptors (glomus cells) is control of pO2 (in contrast with central chemoreceptors, where the main trigger is a change of pCO2/H+). As I said earlier, they are also sensitive to changes in pCO2/H+, but these are secondary. It means that the sensitivity of these receptors to the low pO2 is greater when pCO2/H+ is high.
Activation of peripheral chemoreceptors is low when the partial pressure of O2 is close to the normal (100 mmHg), but when it is below 60 mmHg, the activity increases rapidly due to a decrease in haemoglobin-oxygen saturation.
Peripheral receptors are not desensitized over time.
Two common hypoxic ventilation responses (CO2/pH can stay at the normal level) – reaction to high altitude or high concentration of carbon monoxide in breathing air.
BREATHING CONTROL FOR FREEDIVERS
How can all of this information about breathing be useful for us, Freedivers? During the middle part of the breath hold, when contractions begin, it is a reaction to high CO2/H+ levels sensed by central chemoreceptors. Peripheral chemoreceptors are not playing an important role at this moment since the partial pressure of O2 is close to normal. But close to the end of your MAX attempt, when pO2 is going to be close to 60 mmHg and lower, a reaction from them will contribute to your urge to breathe.
USEFUL LINKS
- https://en.wikipedia.org/wiki/Carotid_body
- https://en.wikipedia.org/wiki/Aortic_body
- https://en.wikipedia.org/wiki/Hypoxic_ventilatory_response
- https://en.wikipedia.org/wiki/Monocarboxylate_transporter
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5037729/?fbclid=IwAR3nDgh7ug_IEySb_VuPk18HxFp0umhjqZCXqr1oe8gf16W9so3MOBLPD04
- https://en.wikipedia.org/wiki/Glomus_cell
- https://www.nature.com/articles/nrn.2018.19?fbclid=IwAR1EWHxSNYGucR4TH4eWlvPWi60Snu4P8DKn4CDZYuJTZ-LcZiP51OZBZ_s
- https://www.researchgate.net/publication/16127919_Blood-Brain_Barrier_Permeability_to_Lactic_Acid_in_the_Newborn_Dog
- https://www.nature.com/articles/nrn.2018.19?fbclid=IwAR1EWHxSNYGucR4TH4eWlvPWi60Snu4P8DKn4CDZYuJTZ-LcZiP51OZBZ_s
- https://study.com/academy/lesson/gas-exchange-diffusion-partial-pressure-gradients.html
Useful videos to watch
- https://www.youtube.com/watch?v=fWBhmrrSPUk&list=LLJQxema4h0Dgx345fC_Q5yA&index=14
- https://www.youtube.com/watch?v=cJXY3Cywrnc&index=18&list=LLJQxema4h0Dgx345fC_Q5yA&t=366s
- https://www.youtube.com/watch?v=ce3RrCl5nwQ&index=22&list=LLJQxema4h0Dgx345fC_Q5yA&t=0s
- https://www.youtube.com/watch?v=8W_u28pxxcw&list=LLJQxema4h0Dgx345fC_Q5yA&index=25&t=0s
- https://www.youtube.com/watch?v=gd3ICLDrO2Q&list=LLJQxema4h0Dgx345fC_Q5yA&index=28
For them, number 1 recommendation – spend some time in advance training your swimming skills. Yes, we have fitness requirements in PADI freediving course. But no worries, it is just basic swimming (200 meters without fins or 300 with fins) and can be performed in any style (also without time limit). If you know, that you cannot meet this requirement, then it is 100% better to train swimming skills before. In some organizations, though there are no requirements for swimming at all. Which seems extremely strange.
What else can be done if you have a few months ahead before the freediving course? You can do some stretching exercises. Stretching is beneficial for freediving, however, it is easy to pass the 1st level without any stretching at all. But if you are going to do advanced or master course, stretching will be super valuable and will help to make the course much safer and enjoyable.
breathing technics for different purposes. You need to focus on relaxation breathing for freediving (here is the
DR is activated when our face is cooled (by cold water for example) or when we hold our breath. When we do both – even better!
reduction of HR for Freedivers (up to 50% or more in highly trained athletes). There are stories with even more impressive results, but let’s skip them now. Sounds impressive? How about this – laboratory rats have 80% decreases in HR while submerged underwater!!
Peripheral vasoconstriction (PV) is a narrowing of the blood vessels to reduce blood flow to non-vital organs (such as skin or inactive muscles, for example) ensuring that oxygen-sensitive organs like the brain or heart receive enough O2 for normal function. In another word PV is a redistribution of blood to vital organs from peripheral organs. PV also induces anaerobic metabolism, with an increase in lactic acid as a by-product. Interesting that the release of lactic acid into the bloodstream doesn’t occur (or at least significantly reduced) until Freediver resurface (at least this is what experiments on laboratory rats show).
why while Freediving you want to pee much often! As you know part of DR is PV and it causes increased blood flow to the torso area and increased blood pressure as a result. Our body detects it and releases a specific hormone responsible for liquid regulations, which increase urine production. Don’t be embarrassed because of it! But make sure that this reflex doesn’t make you dyhadrated (drink enough before and after Freediving session).
First one, let’s call it “old school” relaxation breathing is when you are trying to slow down breathing rate by extending your inhale and especially exhale part. There is even recommendation – exhale twice longer than inhale (not sure why twice). Let’s be honest – it is a mild version of hyperventilation (if you extend your exhale over a period of time, you removing extra CO2 from your body). I think Goran Ccolak said in his interview to Freediving Café, that every breathing, which differs from tidal breathing is hyperventilation. The question is how big ;-).
extending the duration of your exhale, do tidal breathing and then just 1-2 big breath in (with passive exhale) before actual breath hold. Same breathing what you have before you fall asleep. Still better to use diaphragm breathing for it though (it means that you still want to learn and practice it). Let’s say for two minutes you are doing tidal breathing. You relax your muscles and mind. Your heart rate will go down since you are more and more relaxed. And your CO2 level not going to be high as well. But at the same time, it is not going to be below the normal level for this particular level of activity.
The answer is – try to become as much relaxing as possible. Easy to say, hard to do. What I recommend for my beginner students is to “scan” their body during breath hold and check if their muscles relax or not.
still have plenty of O2. Enough for every body’s cells. And you know that and this is why you are keep holding.
Another important rule – do recovery breathe every single time, not only when it was “hard” dive. Even after very easy dive you need to do it – it will help you to create a very useful habit and put it on a subconscious level!
In scuba diving, when you are breathing compressed air underwater, your body is saturated more and more with Nitrogen (79% of the air is Nitrogen). The chain looks like this – you breathe in the compressed air from a scuba tank and now the pressure of N(Nitrogen) in your lungs more than in your blood, so, it going to your blood. And now in your blood pressure of N is higher than in your tissues, so, it is going to your tissues. Until you have an equal pressure of N everywhere (this is what we call saturation). And when you start coming up, opposite happens. Now pressure of N is smaller in your lungs, so the reverse process is happening – from your tissues N going to the blood and then to your lungs and then you exhale it. But it doesn’t happen that quickly. In some tissues, this process is slower than in others.
If they violate these rules, they have a very good chance to have DCS! Without making it too complicated, DCS is when molecules of N combined in your blood (or tissues) in the form of a bubble and can cause very serious damage!
small recovery time has a very good chance to get DCS….What to do, if you are spearfisher? Limit duration of your spearfishing session, have enough rest between dives, use appropriate thermal protection, stay hydrated!
First of all – symptoms of DCS. Type 1 DCS – skin rash on shoulders and upper chest, joint and limb pain. Type 2 DCS – peripheral tingling and numbness, unconsciousness, respiratory arrest and paralysis, coughing, feeling of air-starving.
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?
an urge to breathe – it is simple contractions of your respiratory muscles (diaphragm for example), which are trying to remove CO2 from your body.
(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.
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!
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).