Dave: I’m Dave Asprey with Bulletproof Radio.
Today’s Cool Fact of the Day is that reading is all about carbon dioxide and it has very
little to do with oxygen. Air has about 21% oxygen and the body only needs about 5%.
Today’s guest spoke at the Bulletproof Conference and his name is Robert Lee. Robert’s a research
fellow in Law, Science, & Technology at Stanford and this is his first time coming on Bulletproof
Radio. I invited him to speak at the Bulletproof Conference on his topic that you probably
haven’t heard of. It’s the art of respiratory hacking. It’s about breathing for focus and
performance. You’ve heard me talking about breathing exercises
and doing things like pranayama or yogic breathing, but what Robert has done is look at the very,
very edges of respiration including things like deep diving. He’s looked at the whole
spectrum that you can do for breathing and built around that some practices that can
help you focus and perform better. This is an area where there just isn’t enough information,
so you’re going to learn quite a lot about that.
Stress in your mind finds its way into your body and if you can discover how to relax
your mind by just hacking your breathing, you can turn off that fight or flight response.
That will clear the fog. You can focus on mental performance. This is not a typical
Bulletproof Radio episode because we’re just diving deep on that. Robert is a true biohacker
in that he’s done a lot of this because he’s just interested in it. You’re going to learn
some cool stuff here. Dave: Robert, thank you so much for being
here with us today. Can you tell us what you’re speaking about at the 2014 Bulletproof Biohacking
Conference? Robert Lee: I’m speaking about how to be mindful
and aware of your breathing patterns. That’s, for me, based upon my experience as a freediver
and a freediving instructor. Dave: Tell us how much control do we have
over our breathing? Robert Lee: Breathing is very interesting
in that it’s the only physiological function we have that’s both autonomic and voluntary,
meaning, digestion for instance is autonomic, so we don’t have to think to digest our food.
Whereas, let’s say, doing a bicep curl is purely voluntary. We have to think actively
to do it. Breathing is at the intersection of both. Normally we don’t have to think about
it, but we can easily stop it whenever we want or speed it up, so in that sense, it’s
a very interesting physiological function. Dave: You are a freediver or you were. Can
you tell us about that and how that actually made you aware of your breathing?
Robert Lee: Free diving is simply the sport of diving on breath-hold, so not using scuba
equipment, just taking a deep breath and going down. Some people do it competitively, trying
to set records for depth, for length of time they hold their breath in the pool. I do this
for very much in the mode of somebody who’s a scuba diver. In other words, I like to be
under water, I like to look at the coral reef and the marine life. Freediving is just another
way of doing that. One great advantage of free diving, and obviously
you don’t have as much equipment, but one really great side benefit is dolphins and
other marine mammals actually recognize you almost as one of their own, in other words,
another air-breathing creature in the water. You can imagine scuba divers they find to
be a little bit alien, but freedivers they actually welcome almost as one of their community
now. Under U.S. Law, you’re not allowed to approach marine mammals within 100 yards but
if they swim up to you, there’s really nothing you can do.
When we’re training in Hawaii and teaching classes, often times we have pods of dolphins
come and swimming around with us and they’re very playful with us. I’ve even had baby dolphins,
which are incredibly cute because they’re about four or five feet long, and they’re
swimming and squeaking and what have you. It’s so quiet that you can hear a shrimp crackling
on the reef, because freediving, you’re holding your breath. It’s utterly quiet. You can hear
whales singing in the background if they happen to be nearby. That’s one of the advantages
or beauties of the sport. Dave: At what depth did you need to be in
order to have those interactions? Robert Lee: Well, you don’t necessarily have
to be deep. A lot of marine life, including dolphins, come to the surface, so actually
what I’m saying applies quite a bit to snorkeling, so I think people should spend a lot on snorkeling
when they’re in a beautiful place. Dave: How long do you typically hold your
breath? Robert Lee: Well, I don’t think there’s a
typical. I will, if I’m just casually going on a reef and swimming around and snorkeling,
two, three minutes might be a typical time. I can do more, but I like to emphasize that
for a person to, say, learn to dive to 15, 20 feet for 45 seconds, it’s still very useful
and can enhance the snorkeling experience, because if there’s something down there, you
can go ahead and look at it. It doesn’t have to be an extreme or hardcore sport in that
way at all. Dave: In order to hold your breath for that
length of time, there’s, I’m sure, preparation you need to do in order to fill your lungs
before you actually dive under water. Robert Lee: It’s mostly about relaxation,
both before the dive and during the dive. We all have enough oxygen in our lungs and
our bodies for several minutes. We just are not accustomed to doing that. As long as you
relax, because if you don’t relax, then you’re stressed out, obviously you’re burning more
oxygen. If you can get the art of relaxing beforehand, and relaxing during it, you’re
breath hold can go to several minutes. One application of this I can mention is we
teach big wave surfers the art of breath-hold. They may be surfing and all of a sudden get
hit by a huge wave and get pushed down and may be down for a minute or more. What’s more,
they’ve been exerting themselves and they may not have gotten a full breath because
they crashed all of a sudden, they’re wiped out all of a sudden. In that situation, you
can imagine what you really need to do is learn to relax.
When we teach people, show them they can do three, four, five minute breath-holds in the
pool, then mentally it’s a lot easier for them to say, “Oh, yeah. It’s no big deal.
I’ll just hold my breath for a little while. I maybe have a little bit of an urge to breathe,
but I know there’s plenty of oxygen there for me to last a while.”
Dave: How much does breathing affect human emotion and cognitive function?
Robert Lee: Well, it not only affects it in quite a bit, it also is a tool for getting
information about that, in the sense that because it is autonomic, you can look at someone’s
breathing and have a sense of what their emotional state is like. At the same time, you can tell
them to be mindful of and to change their breathing pattern, and then also affect those
things. Dave: Heart rate variability is a popular
hack amongst Bulletproof biohackers. What is heart rate variability and how does it
affect performance? Robert Lee: Well, I have to say I’m not an
expert on heart rate variability as nearly as much as some of the people at this conference,
including some of the vendors at this conference. In general, my understanding is that it’s
important for there to be a variation in your heart rate over the course of a minute. A
low heart rate is generally associated with cardiovascular health and so is heart rate
variability. In other words, your heart rate should not be just 60 all the time, it should
in fact vary. When I do the type of breathing exercises
that I do before I freedive and that I’m going to show today at the Bulletproof Conference,
my heart rate may be around 70 at the inhalation, but as I exhale and the air comes out of my
lungs and the pressure in my chest decreases, that heart rate will drop into the 40s. It’ll
go from the 40s up to 70 and then back down into the 40s and it will vary like that.
Dave: How did you discover the art of respiratory hacking?
Robert Lee: It really comes from my freediving experience. Now, there are obviously lots
of very ancient arts that focus on breathing, such as pranayama, which literally means something
like breath study or life force study or practice, and qi gong, kundalini. There’s certainly
a huge amount to be learned in those. Freediving is the kind of thing where we try to introduce
people to the art of breathing in just a few days. It’s a little more practical, menu-driven,
do A, B, C. D. There’s no doubt that you seriously get into freediving, a lot of people start
studying those more ancient disciplines. Dave: Sitting here talking about breathing,
I’m very aware of the fact that I’m naturally a shallow breather. It’s making me very uncomfortable
sitting here talking about breathing because I’m aware of my breath right now. Can you
talk a bit about people that are shallow breathers and what that might mean?
Robert Lee: Well, shallow breathing just means you’re not really exchanging your oxygen and
your carbon dioxide as much. It also doesn’t give you a chance to one, induce that heart
rate variability and also do an extended exhale. I know you’re off-camera, but maybe we can
do this a little bit together, what have you. When I do talks about this, I say the quick
lesson is that a long relaxed exhalation is really important to mindful breathing. During
that exhale, as I said, the pressure’s going down in your chest. Your heart rate is dropping
and it’s easy to zone out and really relax doing that.
Now, letting the air out of your lungs, you can also control or meter by closing your
teeth or your lips, pursing your lips and letting the air slowly escape, like closing
the neck of a balloon. An inhale, you might take a couple seconds to do that, and if I
say exhale for a good 8 or 10 or 12 seconds, that might be difficult to do unless you do
what I just said, which is let it escape slowly through your teeth or your lips.
Dave: Is that merely an exercise or can you actually train yourself to breathe naturally
a different way? Dave: It’s both. You do it as an exercise
and then you tend to be able to invoke it when you need to. For instance, when you’re
reacting to a stressful event, I’m sure many of us have heard take a deep breath. Pause
and take a deep breath. I would add to that, take several slow, deep breaths. If you’re
shallow breathing, you can’t do what I just said in terms of taking a nice, long exhale
to relax. In addition, it’s a focus on that long exhalation, several deep, slow breaths
with a nice, long exhalation where you can, like I said, maybe close your eyes and really
just relax and let it out. The exhalation doesn’t take any positive effort. You can
just relax and let it out. Dave: We’ve all heard the term fight or flight.
How does our body and breathing react to a stressful event? Break it down for us.
Robert Lee: Imagine a stressful event, which in pre-modern times might have been encountering
a mountain lion. In modern times, it might be some co-worker yelling at you. Now, in
the mountain lion situation, you take off and you run and you discharge that energy
that your body’s built up. That’s actually a healthy response. When we’re in the office
or any other modern life situations, you can’t physically discharge the stress that’s been
brought out by that. What happens when you encounter that stressful
situation that your sympathetic nervous system is engaged, your heart rate and your respiration
rate go up, and one additional observation that I have had about this physiology, is
that you tend to take a quick inhale, your breath, and hold it for a moment. I think
that literally may be due to the fact that you’re trying to stay as quiet as possible.
You saw the mountain lion, you’re not sure if it saw you, so keep quiet for a second.
If it starts charging you, know it’s seen you, so then you have to take off and run.
Those are the three things that happen when we have a stressful event.
Dave: What is your recommendation for a mindful response to a stressful event, whether it
be seeing a mountain lion or encountering an angry friend or colleague?
Robert Lee: Take a deep breath, as they say, or take several slow, deep breaths and, like
I said, take several slow, deep breaths and focus on a nice, long, relaxed exhalation.
Dave: So much of breathing is involuntary. What are the actual mechanisms of inhalation?
Robert Lee: Well, there are several different muscle groups involved in breathing. The main
one is your diaphragm, which is the dome-shaped muscle at the bottom of your lungs which pull
down and pull air into your lungs. If you watch anybody while they’re sleeping, you’ll
see that that’s really the only muscle they’re engaging. It’s the most efficient muscle to
use to breath. We should naturally try to focus on that. When we get more tense, we
tend to not to engage that as well and invoke other muscle groups, which we can also use,
but the diaphragm is the main one we should focus on and be mindful of.
In addition, you have muscles between your ribs called the intercostal muscles which
are literally the ribs you eat if you’re having a barbecue. Those are the muscles. They can
expand the ribcage as well, but the amount of air they can move is much smaller.
Finally, you can also expand your ribcage by raising your shoulder blades, which adds
just a tiny bit little more air to your breathing. Freedivers actually have a couple more tricks
to add even smaller amounts of air, but that’s not relevant to mindful breathing practice.
Dave: Sometimes deep breathing is really uncomfortable. Is optimal inhalation supposed to feel good?
Robert Lee: Well, I teach maximal inhalation, which is in other words, taking the biggest
possible breath you can, engaging all those muscle groups, your diaphragm, your chest
and your shoulders. That’s good for practice just to see how big a breath you can take.
Obviously, for freedivers, where when you have that one breath to work with, we want
to do that. That’s really just an exercise so that you understand the mechanics of inhalation
better. In general, mindful breathing doesn’t go to that super full point. What it does
is fully engage the diaphragm to fill up your lungs and then adding your chest, what I would
say is about half-way, in other words, slightly more than a normal inhalation.
Dave: We’ve taken a deep breath in, but now let’s talk about the exhale. How important
is the exhale of a breath? Robert Lee: For mindful breathing, I’d say
it’s the key. If there’s one thing you can take away from this, it’s that doing a long
exhale and, as I said, metering the amount of air coming out of your lungs through your
teeth or your lips, will allow you to relax. Even if you ignore everything else, a long
exhale should help you relax. Dave: Should the length of our inhale and
the length of our exhale actually be similar in time or are they different?
Robert Lee: There’s all sorts of different breathing practices. I’m not going to speak
universally, but given what I just said about the long exhalation as a mode of relaxation
… People have different practices and might decide that they only want to do a few breaths
with that long exhalation like I said. In general, the way we teach it in terms of freediving
is that long exhalation. Can you do a 10-second inhalation as well, sure you can, but that’s,
I think, one of those arts that’s probably learned through one of these ancient practices
that takes a while. In general, we teach it’s a normal inhalation that takes a second or
two and then that extended exhale. Dave: For you, what is normal breathing for
you? Robert Lee: Interestingly, I’m not as good
about mindful breathing as I should be, so I should practice what I preach. Certainly
when I’m aware of it, I’ll do it and my exhale will actually extend well beyond that 10 seconds
oftentimes. Ten seconds is not … That precise number is not important, but when I’m really
trying to relax and particularly before a dive, that exhale for me may be 15, 20, even
30 seconds. Dave: I’m sure you talk about breathing a
lot. Some of our listeners right now might be having a similar reaction that I’m having
of being really uncomfortable, because I’m paying so much attention to my breathing.
When you talk about it, do you have a similar reaction with it, being very hyper-aware of
your breathing, and are you comfortable with that?
Robert Lee: Because it is both voluntary and autonomic, obviously it is the kind of thing
that induces that kind of awareness. Like I said, I’m certainly not a naturally calm
person, grace under pressure, ice water in your veins type of person. That’s why I was
attracted to this kind of practice, because it does allow me to do that when I focus.
Like I said, I should probably be better about incorporating it into everyday life, although
I certainly can do it when I’m diving. Maybe even right now we can just take a few
breaths like that way and see if it carries on for the next several minutes, so we’ll
skip for the moment the maximum inhalation. I described it a little bit and you can try
that out. What we’ll do what I said is the mindful comfortable inhalation. First you’ll
inhale with your diaphragm fully, and then you’ll use your chest. I’ll do it once, and
then I’ll have you try it. Diaphragm … and chest … and then I’ll exhale. I feel like
you’re almost falling asleep during that phase, so I’ll talk you through it, okay?
Dave: Okay. Robert Lee: Go ahead and inhale with your
diaphragm. Nice and full using that muscle down there, add in the chest a little bit
so it’s nice and full, but not uncomfortable and then let it out slowly through your lips
… two, three, four, five, six, seven, eight, nine, ten. Inhale again. Inhale with the diaphragm
and the chest, and exhale … two, three, four, five, six, seven, eight, nine, ten.
Inhale again, diaphragm and chest, and exhale … two, three, four, five, six, seven, eight,
nine, ten. Okay, great. Do we feel good about continuing?
Dave: Yes, we do. It is interesting. I’m sure a lot of our listeners were doing it with
me. When I started the exhale through my teeth, I felt a little dizzy, and then I felt myself
calm down. It was really a wonderful experience and I hope everyone else is feeling that.
How do our lungs age? Robert Lee: You know, I’m certainly not an
expert on that. I do know that for freedivers specifically, what’s the great thing about
the sport is that your ability diminishes very little with age. It’s not weight bearing,
you don’t have to worry about dealing with heavy weights. The water is pretty forgiving.
I imagine one day when I’m a lot older, if I’m going diving I may need friends to help
me carry my equipment to the shore and help me get suited up and everything like that.
Once I’m in the water, imagine a baby that has very little muscular development, but
it’s fairly still easy for them to move in the water. There are many freedivers who are
very accomplished freedivers who are literally senior citizens.
Dave: Is holding your breath beneficial to your health or harmful?
Robert Lee: Well, certainly chronically it’s not a good thing. Just like stress in the
short term is a perfectly fine thing. It motivates us, it helps us get things done. If we’re
running away from a mountain lion, it’s a very good thing, but we don’t want to have
it become a chronic thing where we have that stress of seeing a mountain lion be our baseline
level throughout life. That’s what causes problems such as cardiovascular problems and
what have you. Breath holding in many ways would be the same
thing. In fact, people talk about apnea or email apnea. Sleep apnea is when you’re having
trouble breathing while you’re sleeping. Some people have even talked about email apnea
where they take a breath and they’re typing their email and then they let it out. That’s,
I think, an example of chronic stress. In terms of a training modality, in other words,
would doing a five minute breath hold three times a week be good for training? I think
it very much could be. It certainly creates large oxygen debt and extreme aerobic stress,
of course. It also even more so induces metabolic acidosis,
which is the kind of thing that happens whenever you engage in serious aerobic exercise. Freedivers
are able to do that even to a greater extreme. In fact, one fact that might interest medical
professionals is that we can all learn to voluntarily hold our breath until our oxygen
saturation is around 50%, peripheral oxygen saturation. So if you put on a pulse oximeter,
which is a cheap device you can buy at a drug store, a lot of doctors I tell that, think
of it as physiologically impossible until I show it to them. Like anything else, people
can learn to do interesting things. Anecdotally, I’ve heard one person say that
he did nothing but breath holds for a month as exercise, literally nothing but breath
holds lying in bed, and he lost six pounds. Could it be the new weight loss fad? Perhaps,
I’m not sure simply because it’s not an easy thing. In other words, the first one or two
or even three minutes of a breath hold when you’re trained are pretty easy, but that last
minute where you’re getting the strongest effects does take a lot of focus. I know some
doctors who think it would be a very interesting training tool and hope to see it gather some
momentum, but right now it’s more just something that we need to do some studies about. I can
just tell you anecdotally some of the things that I’ve seen.
Dave: So you brought up sleep apnea. Can some of these breathing exercises actually help?
Robert Lee: Well certainly I’m not an expert in sleep apnea, but to the degree that you
can improve your breathing mechanics, and to the degree that you can become more relaxed
and more mindful, I would think it would help. Now on the other hand, when we’re sleeping
we all tend to breathe fairly well. The stress goes down, we breathe with our diaphragm,
so sleep apnea may be mostly a result of physiological issues such as a tongue rolling into the back
of the throat or something like that, which I’ve heard about, that you may not really
be able to fix through this sort of thing. I suppose it couldn’t hurt to try.
Dave: What about people that have asthma? Robert Lee: Asthma, certainly I can’t talk
about counter indications, in other words, whether holding your breath for a long time
could induce certain issues. There’s certainly, you can imagine at the end of a long time,
you’re under extreme stress and you’re breathing really, really hard and that can cause some
kind of bronchial spasm or something, for all I know. The mindful breathing part where
you’re inducing relaxation, what have you, I would imagine that would be helpful.
Dave: Why is holding your breath so uncomfortable? Robert Lee: Well there’s a few reasons. One
is that we’re simply not used to it, so in some seminars I will have people do a simple
one minute breath hold just to see what it’s like. The discomfort there is not from lack
of oxygen, because we have plenty of oxygen to last well beyond a minute and you’re barely
tapping into your reserves at that point. The main reason is simply that you are not
used to your chest not moving for a full minute. It’s just uncomfortable. How many times have
you done that in your life? Maybe a handful, like when you were a kid and you challenged
some friends to a breath holding contest and you did that a few times in junior high school
or what have you, but when’s the last time you did it? Maybe never.
The initial training there is just getting used to that fact. In fact, when people take
freediving seminars they often ask me, they say, “If I’m getting uncomfortable at the
end, can I slowly let some air out?” and I say, “You know, you can do that, but that’s
kind of a beginner’s trick,” because, again, they’re not used to that complete lack of
movement. Very quickly divers stop with that trick because they realize they want to keep
the air in and they’re just used to that static state.
Once you get two minutes into a breath hold, then you’ll start to get a stronger urge to
breathe and that also doesn’t come from lack of oxygen. It comes from the increase in carbon
dioxide. The carbon dioxide waste product in our bodies is the proxy generally for low
oxygen, because our carbon dioxide chemoreceptors are much simpler than oxygen chemoreceptors.
They developed evolutionarily first and most organisms use carbon dioxide as a proxy or
an inverse proxy for oxygen. They’re saying, “Hey, your carbon dioxide is high,” meaning
your oxygen is probably low. Dave: With the build up of carbon dioxide
, is that a bad thing when you’re holding your breath?
Robert Lee: In the short term it’s not a bad thing. It’s a stress. I like to talk about
the stress in terms of you stress and distress. Running is stress. In fact, while you’re running,
you have a higher chance of having a heart attack than while you are sitting on the couch,
but nonetheless we do it because our bodies adapt to that stress well, and it’s therefore
a you stress. Breath holding in limited form and in the ways we have discussed, can be
a form of you stress. Dave: Can you give us a few real life scenarios
about how we can apply mindful breathing? Robert Lee: Well, sure. When I’m doing a freedive,
typically I will do this type of breathing for up to eight minutes. In those situations,
we’re really trying to oxygenate ourselves fully and make sure we’re lying wholly still,
so literally we’ll lie in the water still for eight minutes, breathe like this and then
do the dive. That’s a fairly long time, but you can do it for just a few minutes in any
kind of situation. Imagine you’re playing golf and you’re walking
up to the putting green and getting ready to putt. Do this as you’re walking up to the
green and it should put you in a more focused state. By and large, when people are anticipating
a performance, they get overly amped, overly hyped up about what they’re going to do and
that can detract from performance. This will help reset that to an appropriate level. Even
one or two breaths can help. For instance, imagine you’re playing basketball
and you just scored a basket to tie the game and you got fouled. You might need to take
a few deep breaths to blow off some of that carbon dioxide, but then as you’re walking
to the free throw line, you can take one or two of these breaths and maybe we can visualize
that right now. Go ahead, close your eyes. Like I said, you
just got fouled. You scored the basket to tie it. You have one free throw you’re awarded
to win the game. You take a few deep breaths to blow off some of that carbon dioxide. Now,
inhale … and exhale … two, three, four, five, six, seven, eight, nine, ten … and
inhale and exhale. The referee bounces you the ball … four, five, six, seven, eight,
nine, ten. You take one more inhale, and you shoot the basketball. There you go.
That’s a scenario in which you can apply that. In addition, mindful breathing as a steady
state thing can definitely help focus and flow overall. It’s a very important part of
flow state and in fact, Steve Kotler talks about the respiratory component of flow state.
Dave: Is the Bulletproof Biohacking Conference important to you as a biohacker and to the
work you do? Robert Lee: It definitely is in the sense
that I’m trying to help people improve their performance and their everyday life through
this one modality of breathing. People here at the conference are attacking that from
all different angles, so I hope this is one relatively straightforward easy tool that
people can add to their kit. Dave: Well, let’s end with, what are your
top three recommendations for kicking ass at life and being bulletproof?
Robert Lee: That doesn’t necessarily have to do with breathing?
Dave: It can have to do with anything you want.
Robert Lee: Well, one we’ll say is the breathing and which we’ve talked about for the past
half hour or so. The other I would say is not caring what people think or not worrying
how you’ll be judged. Again, as Steve Jobs famously said, “We’re all going to die pretty
soon anyway, so what does it matter.” Let’s just go and … Carpe diem, as they say. I
don’t know if that’s two or three, but maybe we’ll count that as three.
Dave: Let’s count it as three. Robert Lee: Okay.
Dave: Robert, thank you so much for being here with us today.
Robert Lee: Thank you for having me. Dave: If you’re looking for a way to know
which foods are making you weak, check out the free app called Bulletproof Food Sense.
It works by using the phone camera in order to get a measurement of your heart rate, or
you can just type in your heart rate if you know what it is from some other monitoring
device. You do this before a meal and you do it after a meal a couple times.
Based on changes in your heart rate, the application can help you to identify which foods are causing
an immune response in your body. Based on that, you can choose to avoid those foods
and you’ll find a huge boost in your performance just from not eating the foods that you have
sensitivities to. You’ll also find that you can lose weight much more easily when you’re
not eating foods that cause you to feel foggy and inflamed all the time. This app is free.
It’s called Bulletproof Food Sense and it’s available on the iPhone Store.
You can also take a step further. Check out Bulletproof HRV Sense. That stands for heart
rate variability sense. Bulletproof HRV Sense goes a step beyond Food Sense and it works
with a wireless heart rate monitor that goes around your chest. You wear the heart rate
monitor and it’ll talk to your iPhone or your tablet and it’ll show you your stress levels
throughout the day. It’ll help you know whether you’re over trained, over stressed or even
just help you know which meetings are causing the most stress in your nervous system, so
you can learn to take control of that stress. This is an awesome app. Number one, Bulletproof
Food Sense is free and number two, Bulletproof HRV Sense is a few dollars and it makes a
huge difference in how you manage and control your stress. Featured
Robert Lee Performance Freediving
Performance Freediving on Facebook Twitter � @BreathHolder Resources
Freediving Train Your Heart & Brain to Work Better Together
� Heart Rate Variability (HRV) Pranayama
Diaphragm and lungs Intercostal muscles
Mindfulness breathing Sleep apnea (Mayo Clinic)
Metabolic acidosis Blood oxygen saturation test (Harvard Medical
School) Pulse oximeter, Blood oxygen monitor
CO2, brainstem chemoreceptors and breathing (Progress in Neurobiology)
Eustress vs Distress (Brock University) Bulletproof
2014 Bulletproof Biohackers Conference Bulletproof Toolbox
Podcast #185, Robert Lee 17 � The Bulletproof Executive 2013