CO2 Tolerance Training

The brainstem CO2 sensor protects the brain from pH shifts that would throw it out of whack

A second breathing oscillator near the facial nucleus was initially thought to be a CO2 chemoreceptor.

"That is, we want to keep carbon dioxide levels, particularly in the brain, at a relatively stable level because the brain is extraordinarily sensitive to changes in pH."

Vagus nerve stimulation reduces depression; breathing rhythm is a natural vagal signal

Artificial vagus nerve stimulation helps depression.

"But the other thing with the hyperventilation, hypoventilation, or the apnea, is your CO2 levels are going from low to high."

Episodic hypoxia vs. breath holds: CO2 stays stable in one but rises in the other

During breath holds, both O2 drops and CO2 rises. During episodic hypoxia, O2 varies but CO2 stays normal -- a key distinction.

"When you hold your breath, your oxygen levels are dropping, your CO2 levels are going up. When you're doing episodic hypoxia, your CO2 levels are going to stay pretty normal. Of course, you're still breathing. It's just the oxygen levels are gone. So unlike normal conditions, which you described before, where oxygen is relatively constant and CO2 is fluctuating depending on emotional state and activity and things of that sort. In episodic hypoxia, CO2 is relatively constant, but you're varying the oxygen level coming into the system quite a bit. I would say it's relatively, I would say CO2 is relatively constant, but it's not going to go in a direction which is going to be significantly far from normal."

CO2 tolerance and anxiety: how slow breathing restores carbon dioxide levels to reduce panic

Anxious people often hyperventilate, depleting CO2. Training slower breathing restores CO2 levels and relieves anxiety.

"That's going to change your pH level. I have a colleague, Alicia Moret, who is working with patients who are anxious, and many of them hyperventilate."

Why we breathe: oxygen in, CO2 out -- but CO2 is not the villain you think

A common misconception is that CO2 is purely bad. You actually need CO2 to liberate oxygen from hemoglobin and deliver it to tissues.

"And of course we breathe in order to bring oxygen into the body, but we also breathe to remove certain things from our body, in particular carbon dioxide."

Mechanical breathing system: nose, mouth, larynx, diaphragm, and intercostals

Understanding breathing mechanics -- lungs, diaphragm, intercostals -- unlocks control of stress, focus, sleep, and mood.

"When we're thinking about the respiration system, we also need to look at the mechanical system."

You need CO2 to liberate oxygen from hemoglobin -- the Bohr effect

Carbon dioxide is essential for oxygen delivery. Without adequate CO2, hemoglobin holds onto oxygen too tightly and tissues become oxygen-starved.

"You require carbon dioxide in order to liberate oxygen from hemoglobin."

High altitude: low air pressure means more breathing effort and CO2 disruption

At high altitudes, the O2/CO2 balance is disrupted because more energy is needed to inhale equivalent oxygen.

"If you're at a high altitude and the air pressure is very low, you have to put a lot of energy into breathing air into your lungs to get an equivalent amount of oxygen."

Opioid overdose kills by shutting down the pre-Botzinger breathing center

Fentanyl and opioids bind to receptors in the pre-Botzinger complex and shut down autonomous breathing, the primary overdose cause.

"You want to breathe in a healthy manner at rest. The best way is to spend maybe a minute each day paying attention to how quickly you are breathing per minute."

CO2 tolerance test: time your full exhale to assess your breathing health

Exhale fully and time it. Under 20 seconds = low CO2 tolerance, 20-50 = moderate, 50+ = high. This is independent of cardiovascular fitness level.

"And if, for instance, you were able to go 50 seconds or longer for that discard until you hit lungs empty, you have a fairly high degree of carbon dioxide tolerance."

Physiological sigh engages intercostals and diaphragm -- feels like a sharp second inhale

The double inhale requires active engagement of intercostal muscles and diaphragm.

"It feels like the only way I can describe it really is as a sharp second and third inhale, because you really have to engage the musculature of those intercostal muscles in the diaphragm in order to do it. And then that long exhale can be through the nose or the mouth, but I find it particularly relaxing or even pleasant to do it through the nose. This method of three can be through the nose or the mouth, but I find it particularly relaxing or even pleasant to do it through the nose. This method of three inhales through the nose, followed by a long exhale through the nose or mouth will eliminate hiccups right away, because what it does is it hyper excites the phrenic nerve three times in a row, a very unnatural pattern for the phrenic nerve to fire. And then it undergoes a hyperpolarization, as we call it, in which the phrenic nerve actually stands a much lower probability of getting activated again for some period of time afterwards. So it is important that you try and return to normal cadence of breathing after doing this three inhales followed by the long exhale. If you need to perform it a second time in order to eliminate hiccups because they're simply not going away, that's fine. You can do that. But as far as we know, this is the most efficient and science-supported way to eliminate hiccups. Now, up until now, I've been talking about breathing techniques, and I've mainly focused on breathing techniques that emphasize the exhale, whether or not it's the carbon dioxide tolerance test, whether or not it's cyclic sighing or the physiological sigh that you use in real time to reduce stress. One thing that we haven't talked about so it's cyclic sighing or the physiological side that you use in real time to reduce stress. One thing that we haven't talked about so much is cyclic hyperventilation. Cyclic hyperventilation, as you recall, is a bout of 25 or so breaths, inhaling deeply through the nose and then passively exhaling or sometimes actively exhaling, typically through the mouth. So it might look like this."

Inhale-emphasis breathing improves focus and information retrieval

When inhale duration exceeds exhale duration, the brain shifts into a more focused mode with better memory access.

"If you're learning from and or enjoying this podcast, please subscribe to our YouTube channel. That's a terrific zero cost way to support us. In addition, please subscribe to the podcast on Spotify and Apple. And on both Spotify and Apple, and on both Spotify and Apple, you can leave us up to a five-star review. If you have questions for us or comments about the podcast or guests that you'd like me to include on the Huberman Lab podcast, please put those in the comment section on YouTube. I do read all the comments. Please also check out the sponsors mentioned at the beginning and throughout today's episode. That's the best way to support this podcast. Not so much on today's episode, but on many previous episodes of the Huberman Lab podcast, we discuss supplements. While supplements aren't necessary for everybody, many people derive tremendous benefit from them for things like improving sleep, hormone function, cognitive function, and so on. The Huberman Lab podcast is now partnered with Momentus Supplements. We've done that for several reasons. First of all, Momentus Supplements are of the very highest quality. Second of all, Momentus supplements are of the very highest quality. Second of all, momentous supplements tend to center around single ingredient formulations. This is incredibly important because if you're going to include supplements in your daily regimen, you're going to want to use the right supplements and the right dosages, and you want to do that in the most biologically and cost-effective way. And single ingredient formulations are the only way that you can determine what works and what doesn't work for you. And it's the only way in which you can adjust the dosage of given supplements, or maybe even alternate days that you take one and not the other, in a way that really allows you to home in on which supplements are going to be ideal for your mental health, physical health, and performance. Also, Momentous Supplements ship internationally, and that's great because we know a number of you reside outside of the United States. If you'd like to see the supplements discussed on the Huberman Lab podcast, you can go to Live Momentous, spelled O-U-S, so livemomentous.com slash Huberman. If you're not already following us on social media, we are Huberman Lab on Instagram, Twitter, Facebook, and LinkedIn. And I should mention that on all those platforms, I discuss science and science-related tools, some of which overlap with the contents of the Huberman Lab podcast, but much of which is distinct from the content of the Huberman Lab podcast. Again, it's Huberman Lab on all social media platforms. And if you haven't already subscribed to our Neural Network newsletter, it is a zero-cost monthly newsletter in which we give summaries of podcast episodes and toolkits, for instance, toolkit for sleep, toolkit for managing dopamine, toolkit for deliberate cold exposure."