- Hey Brian, great to see you. - Good to see you, Andrew. - Brian McKenzie, world expert in human performance, breath work, AKA respiration physiology and its application to things related to mental health, physical health and performance. So if you're an athlete, a student, a parent, a teacher, or just somebody interested in the use of respiration, AKA breath work, in order to understand and regulate your physiology and psychology, the work that Brian does is absolutely first rate and important, I believe, to know about.

Without further ado, let's talk about the carbon dioxide tolerance test, what it's good for and how to do it. - Yeah, well, the carbon dioxide tolerance test was something that we created kind of like it's our own little HRV, right? - Heart rate variability. - Yeah, heart rate variability screen without using the technology, right?

Keeping us as the technology. So ideally the setting is you're either lying down or you're sitting up. It's the same thing every time you do it. You don't need to do it every single day per se, but when you first get started with this, that is the best bet and doing it the same way each time.

If you don't, you're gonna be changing a number of the variables that could be occurring, much like you would do with an HRV assessment in the morning, right? So ideally you're sitting or relaxed for a couple minutes. You're either lying down or seated at the first time you're doing it.

And then what we do after a couple of minutes is you would take a full inhale through the nose and you're going to exhale as long and or as slowly redundant as possible through the nose only. The reason we don't use the mouth is because I can purse my lips and I can control a lot of the variables that we're looking at here.

One of those variables is a mechanical issue that may be occurring with, let's say the diaphragm and intercostals on the eccentric control of that exhale and glottal control, right? That goes kind of out the door if I can purse my lips. So people can actually extend this or prolong it with a mouth exhale versus the nose inhale, but you can get good at this with the nose exhale and essentially do the same thing.

- So let me make sure I understand. So sit down, relax, or lie down, relax. - Couple of minutes. - Then a big inhale. - Full inhale. - Lungs full. And then a slow controlled exhale, what you're calling the eccentric portion of the breath through the nose. - Through the nose.

- Because doing it through the mouth, there are just too many variables related to all the things you mentioned that can allow someone to adjust that duration. But through the nose, it's more objective. Is that right? - Correct, correct. And obviously you're gonna have a timer with you. So the moment that you hit the top end of your inhale, the timer starts and you begin to exhale.

If you're questioning the exhale at all, the easiest thing to do is just to cover your nostrils and you should feel a slight pressure that's still occurring due to the exhale happening. You can cover the nostrils and there will be pressure and you can just remove them once you have the pressure, once you feel the pressure and continue to exhale.

- So before we go any further, maybe we just try that first piece. - Go for it. - All right, so when it hits that five mark, I'll go. (inhales) All right, all right. - Which is actually, I mean, and your time is pretty good considering the fact that we're sitting here talking.

You didn't have time to relax, right? That's not, I would not use this, even though you did that right here, that wouldn't be an accurate assessment of what your morning kinda, let's call it readiness would be, right? - So ideally I'd take that two minutes or so rest, sitting or lying down.

Okay, then do that. The duration there for me was a little over 25 seconds or something on the exhale. I noticed that when I inhale all the way, the temptation is to hold my breath before I start, but you said you immediately wanna reverse into the exhale. - Yeah, you wanna start into that exhale.

- So at a very coarse level, if somebody has a very short exhale time, let's say the total duration for them to get to lungs empty on that exhale is 10 seconds or less, versus 20 to 30 seconds, versus 60 to 90 seconds. What general sorts of information is that giving them about the state of their physiology?

- That's a really good question, because what we've been able to uncover, and this, you know, with the help of Andy Galpin and his lab, for the lower scoring, that there is definitely a lean towards more of a state anxiety. Now, I say state for a very important reason.

This is not a diagnosis, right? I am not diagnosing anxiety that is not what the, we're talking on a scale of arousal, my state is probably a little more anxious. So I've probably been a little more revved up. You just fit into that category. Under 30 seconds is where we start to fit into that category, right?

But that would make sense for somebody who is more in, you know, had no practice, no calming down effects. - I've been drinking a little bit of caffeine. - You've been drinking a little caffeine, we're ramped up a bit. Like you didn't have any, right? Like, so having a lower score is going to just mean I'm a little bit more ramped up, things going on.

- Sympathetically leaning, right? So I've got more sympathetic tone going on. - Some people will hear that and they'll think sympathy. We're talking about the so-called sympathetic arm of the autonomic nervous system, which is nerd speak for the aspect of our nervous system that's associated with alertness and arousal as opposed to parasympathetic, which is generally associated with states of more calm, sleep, the so-called rest and digest system.

So we say sympathetic leaning for somebody who has a carbon dioxide discard rate of, you know, 30 seconds or less, it's that they're kind of, they're alert, they're awake. It doesn't necessarily mean they're having an anxiety or panic attack, they're just alert. - Yeah, I mean, if you're working out, you're not going to exhale very long, right?

Like you've got a lot of buildup of a lot of things going on including your sympathetic nervous system and CO2 because of the energy demand of what's going on. So that said, when we, with people who score under that 30 second mark, when applying this assessment, we have them start with more basic protocols, right?

So this would just simply be more of an equal in and out, just working that in and out based off of the scoring that was going on with that. Then as we get up above 30 seconds and move into the 30 to 45 second range, that gets a little bit more difficult in ranging, right?

So what we use with rhythms starts to change. We go to a more complex rhythm. Ultimately, as we get up into the higher ranges of the exhale assessment or the-- - So 60 seconds, 90 seconds. - Yeah, yeah, getting up above roughly 60, 70 seconds, you're going to see your apnea protocols, right?

These are things that are more advanced protocols and in fact, you would get into more of the breath hold work per se, like let's just say static apnea work. - Okay, so carbon dioxide blow off time, which means it takes X number of seconds to go to completely lungs empty, the way you described before, of 30 seconds or less is more sympathetic leaning, meaning more alert, maybe a little bit anxious.

35 to 45, maybe 60 seconds, calmer. - Yep. - 60 to 90 seconds. - You're in your normal range around 45. This is an absolutely normal range with somebody who hasn't tested, who's calm. That is a very normal range. - So 45 second discard rate would be a good goal for people.

- Correct. - Okay, got it. So if we take a step back and we just look at this test, what is it good for? When could one use it? I know it has multiple uses. In other words, why do this test in order to determine one's underlying physiology? Is it, for instance, post-exercise as a way to determine whether or not you've calmed down and entered a recovery state?

I know Dr. Andy Galpin's really big on this. He talked about it on our podcast and elsewhere that after a hard workout, it's a great idea to do three to five minutes of down-regulation breathing, exhale-emphasized breathing, or something to down-regulate meditation, just something to calm down, enter the recovery phase.

I suppose one could then do the carbon dioxide tolerance test at the end of that to determine whether or not they are, in fact, calm. Would that be one potential use? - Yeah, you could implement it there. The easier thing would just, knowing, you're gonna see a much shorter assessment.

- So people should be aware. What about on waking? When people wake up first thing in the morning, is it a good idea to do it in bed in the morning? - I wouldn't say in bed. I would say give it like 15 minutes, get out of bed, do a few things, go to the restroom, get some water in you, then go lie down or go sit down, chill out for a couple of minutes, then do it.

- When else have you applied this? Like when you teach it to athletes, military, CEOs, high performers, is it something to do before they go out on stage, something to do mid-competition? What are some other applications? - So what I do, the application I use it for is to identify breathing protocols where that individual's at.

Once we get good at this, once we have a rhythm and where I can see a baseline is, I stop doing it every day. We then apply it maybe weekly or even monthly based on, I give them breathing protocols. Based on that assessment, for the general population, for everybody, obviously we've got rhythms that are associated with that and a calculator that people can input to actually get those rhythms and to apply those rhythms for roughly three to five minutes whatever after they're done.

- Hey Dozer, Brian's dog Dozer has got a giant head and he's a beauty, goodness gracious. He's got, his head's easily as big as Costello's. - Oh yeah, he's-- - Okay. So he's a nasal breather, if you notice. He's a calm dog. At this point, it's clear what the carbon dioxide tolerance test is and that the number that you get consistently over time, say in the morning-- - It's important.

- Sounds like it's a good idea to do in the evening too. - Let's apply a scientific method to your own world here, right? And this is easy for people to do because we've got all the information up that they can actually input and go, oh, I've got a different protocol in the evening than I do at night, oh, and I'm also very different after training, so just using this assessment gives you an actual timeframe for what's happening and we've collected and had enough information to understand where you would fit inside of a, you know, the schema of, hey, whether I'm up, ramped up sympathetic or I'm actually more parasympathetic charged, right?

Or down-regulated, I should say. - Yeah, I've found the carbon dioxide tolerance test just to be a great available anytime measure of internal state. And by doing it in the morning, and now it sounds like I should also do it in the evening, interesting, I mean, the whole thing only takes three minutes total.

And you can just note the number in your mind or write it down, put it in your phone. It gives you this baseline evaluation of sort of how you're progressing through life in terms of managing your internal state. So thank you for explaining carbon dioxide tolerance test. - Yeah.

- Give it a try, folks. It's very informative. It takes only about three minutes, zero cost. Very easy to do. You'll get interesting information about your particular physiological state at that time. But if you do it a few times consistently, you'll get really interesting information. And Brian McKenzie and colleagues have developed a terrific zero cost website.

It's shiftadapt.com/breathwork, where you can take your carbon dioxide tolerance time, you enter it into a table there, and it will give you really useful information about certain breathwork protocols and how to do them specifically. The duration of inhales, breath holds, and exhales. Again, that's completely zero cost. So a terrific resource.

Thank you, Brian, for providing that resource. Shiftadapt.com/breathwork is where you can plug in your carbon dioxide tolerance test results and apply those to improve any aspects of your mental health, physical health, or performance that you're interested in.