urge to breath Archives

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).

breathing for freedivers (central chemoreceptors)

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

Useful videos to watch

Tag: urge to breath

Breathing For Freedivers (Part 1)

1. CENTRAL CHEMORECEPTORS

2. PERIPHERAL CHEMORECEPTORS

BREATHING CONTROL FOR FREEDIVERS

USEFUL LINKS