ANDREW HUBERMAN: Hey,
Brian, great to see you. BRIAN MACKENZIE: Good
to see you, Andrew. ANDREW HUBERMAN: Brian
Mackenzie, world expert in human performance, breathwork, a.k.a. 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, a.k.a. breathwork, 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. BRIAN MACKENZIE: Yeah, well, the
carbon dioxide tolerance test was something that we created-- it's our own little HRV. ANDREW HUBERMAN: Heart
Rate Variability. ANDREW HUBERMAN: Yeah, heart
rate variability screen without using the
technology, be-- 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
going to be changing a number of the variables
that could be occurring, much like you would do with an
HRV assessment in the morning. So ideally you're sitting or
relaxed for a couple of minutes. You're either lying down
or seated 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
the glottal control. That goes 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. ANDREW HUBERMAN: So let
me make sure I understand. So sit down, relax
or lie down, relax-- BRIAN MACKENZIE:
A couple minutes. ANDREW HUBERMAN:
--then a big inhale-- BRIAN MACKENZIE: Full inhale. ANDREW HUBERMAN: --lungs
full, and then a slow, controlled exhale-- what you're calling
the eccentric portion of the breath-- through the nose. BRIAN MACKENZIE:
Through the nose. ANDREW HUBERMAN: 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? BRIAN MACKENZIE:
Correct, correct. And, obviously, you're going
to have a timer with you. So the moment that you hit the
top end of your inhale [INHALES] 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. ANDREW HUBERMAN: So
before we go any further, maybe we just try
that first piece. BRIAN MACKENZIE: Go for it. ANDREW HUBERMAN: All right. ANDREW HUBERMAN: So when it
hits that five mark, I'll go. [INHALES SHARPLY] [EXHALES] All right. All right. BRIAN MACKENZIE:
Which is actually-- I mean, your time is pretty
good considering the fact that we're sitting here talking. You didn't have time to relax. 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, let's
call it readiness, would be. ANDREW HUBERMAN: So, ideally,
I'd take that two minutes or so rest sitting
or lying down. BRIAN MACKENZIE: Yeah. ANDREW HUBERMAN:
OK, then do that. The duration there for me
was a little over 25 seconds or something on the exhale. BRIAN MACKENZIE: Yeah. ANDREW HUBERMAN: I noticed
that when I Inhale all the way, the temptation is to hold
my breath before I start. BRIAN MACKENZIE: Yes, of course. ANDREW HUBERMAN: But you
said you immediately want to reverse into the exhale. BRIAN MACKENZIE: Yeah, you
want to start into that exhale. ANDREW HUBERMAN: 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. BRIAN MACKENZIE: That's
a really good question. Because what we've
been able to uncover-- and this-- 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. I am not diagnosing anxiety. That is not what-- 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. But that would make sense
for somebody who is more-- had no practice, no
calming down effects. ANDREW HUBERMAN:
I've been drinking a little bit of caffeine. BRIAN MACKENZIE: You've been
drinking a little caffeine. We're ramped up a bit. You didn't have any-- so having a lower score
is going to just mean, I'm a little bit more ramped up,
things going on, sympathetically leaning. So I've got more
sympathetic tone going on. ANDREW HUBERMAN: Some
people will hear that and they'll think sympathy. We're talking about-- BRIAN MACKENZIE: No. ANDREW HUBERMAN: --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-- BRIAN MACKENZIE: Correct. ANDREW HUBERMAN: --sleep,
the so-called rest and digest system. BRIAN MACKENZIE: Correct. ANDREW HUBERMAN: So when we say
sympathetic-leaning for somebody who has a carbon dioxide
discard rate of 30 seconds or less it's that they're
alert, they're awake. It doesn't necessarily mean
they're having an anxiety or panic attack. BRIAN MACKENZIE: Correct.
If-- ANDREW HUBERMAN:
They're just alert. BRIAN MACKENZIE: Yeah, I
mean, if you're working out, you're not going to
exhale very long, 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. ANDREW HUBERMAN: OK. BRIAN MACKENZIE: 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
seconds and move into the 30- to 45-second range, that gets
a little bit more difficult in ranging. 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-- ANDREW HUBERMAN: So 60
seconds, 90 seconds-- BRIAN MACKENZIE: Yeah, yeah. Getting up above
roughly 60, 70 seconds, you're going to see
your apnea protocols. These are things that are more
advanced protocols and, in fact, you would get into more of
the breath hold work per se. Let's just say
static apnea work. ANDREW HUBERMAN: So carbon
dioxide blow off time, which means it takes X
number of seconds to-- BRIAN MACKENZIE: Yeah. ANDREW HUBERMAN: --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. BRIAN MACKENZIE: Yep. ANDREW HUBERMAN:
60 to 90 seconds-- BRIAN MACKENZIE: 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. ANDREW HUBERMAN: So 45-second
discard rate would be a good "goal" for people. BRIAN MACKENZIE: Correct. ANDREW HUBERMAN: OK, 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
is 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 downregulation breathing, exhale-- emphasize 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? BRIAN MACKENZIE: Yeah, you
could implement it there. The easier thing
would just knowing-- you're going to see a very-- you're going to see a
much shorter assessment. ANDREW HUBERMAN: So
people should be aware. What about on waking,
when people wake up first thing in the morning? BRIAN MACKENZIE: Yeah. ANDREW HUBERMAN:
Is it a good idea to do it in bed in the morning? BRIAN MACKENZIE: I
wouldn't say in bed. I would say give it 15 minutes,
get out of bed, do a few things, go to the restroom, get some
water in you, then go lie down, go-- or go sit down, chill
out for a couple of minutes, then do it. ANDREW HUBERMAN: 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? BRIAN MACKENZIE: I usually-- 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. There-- 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 their-- ANDREW HUBERMAN: Hey, Dozer. Brian's dog, Dozer,
has got a giant-- he's got a giant head and he's
a beauty, goodness gracious. He's got-- his head's as
easily as big as Costello's. BRIAN MACKENZIE:
Oh, yeah, he's-- ANDREW HUBERMAN: OK, so
he's a nasal breather. BRIAN MACKENZIE: Down. ANDREW HUBERMAN: 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 and-- BRIAN MACKENZIE: It's important. ANDREW HUBERMAN: Sounds
like it's a good idea to do it in the evening too. BRIAN MACKENZIE: Let's
apply a scientific method to your own world here. 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 time frame for what's happening. And we've collected and
had enough information to understand where you
would fit inside of a sche-- the schema of, hey,
whether I'm up-- ramped up, sympathetic or I'm actually
more parasympathetic, charged-- or downregulated, I should say. ANDREW HUBERMAN: Yeah, I've
found the carbon dioxide tolerance test is 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. It's-- I mean only-- the whole
thing only takes three minutes total. BRIAN MACKENZIE: Yeah. ANDREW HUBERMAN:
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 how you're progressing
through life in terms of managing your internal state. So thank you for explaining
carbon dioxide tolerance test. BRIAN MACKENZIE: Yeah. ANDREW HUBERMAN:
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.