This particular table
is going to go over
an example of what can happen
during breath hold-diving.
We have O2 concentrations and CO2.
Both in terms of percents
and millimeters of mercury.
During the resting condition,
this is the alveolar gas, is around
14% or 100 millimeters of mercury.
The carbon dioxide
concentration is about 5.6%
and that encompasses 40
millimeters of mercury.
Now, right before descent,
sometimes, people will
hyperventilate a little bit.
And they do that so
that they’ll be able to
hold their breath for a
longer period of time.
So just before the descent, the
increase in O2 will go up to 16.7%.
And the barometric pressure stays at
760, but the O2 pressure goes to 120.
Carbon dioxide gets blown off a little bit
so it went from 5.6 to 4,
that decreased the
partial pressure to 29.
Now what a person does is
they go underneath the water
so this is after they have –
right before they descended,
they now are diving down deeper.
At the apex of their dive, the
oxygen concentration drops to 11%.
However, look at the partial
pressure of O2.
more than what you started with.
In terms of carbon
it is at 3.2% or, in this case,
about 42 millimeters of mercury.
But it’s this oxygen that at the lowest
portion of the dive at the apex,
you don’t have a problem with O2.
Why? Because barometric
pressure’s so high.
Where the clinical problem comes
in with breath hold-diving
is if someone goes to the surface too quickly
after they’ve depleted their oxygen.
So as they are starting to
go towards the surface,
continues to decrease.
Now, it’s only about 5.9%.
But this is the very big problem, oxygen
drops to about 41 millimeters of mercury.
At this point, the
person can black out.
Blacking out while under
the water is not good.
This could involve a terminal condition
or the person might die because
they passed out underneath the water
and will then of course drown.
It’s interesting that barometric pressure
makes such a difference in this case
because notice that at
the apex of the dive,
of O2 were so high,
they were just high
because of the high barometric
pressure of the water.
This is an example of someone
who is holding their breath.
This first part is the
start of a breath hold.
This is the start in which the body
is really, really trying to breathe
and then this is the end
of the breath hold.
So let’s look at the process the body
does to try to hold their breath.
This particular diagram shows
a number of pressures.
This interesophageal pressure or
IEP being the most important.
So if you look at
when you do a breath
hold, it’s fairly stable
until the point at which the body
is really trying to breathe.
And this forms a number
of various portions
that cause these Muller
and Valsalva maneuvers.
And you’ve all probably
And so after this particular lecture, I
encourage you to take a breath hold.
Take in as much air as you can, hold
your breath for as long as you can.
You’re eventually going to reach a point in
which the body’s really trying to breathe.
And that is the point in which these
Muller and Valsalvas kick in.
And then finally, you have the point at
which you can no longer hold your breath
and that’s when carbon
dioxide levels get too high.
So what kind of adaptations occur when
someone is trying to do breath holds?
And how can you improve
someone’s breath hold time?
Well, breathing faster is kind of interesting
in that it blows off carbon dioxide
so you can actually
hold your breath longer
if you hyperventilate
before you breath hold.
And it’s interesting that it’s not because
you get more oxygen into your lungs.
It’s because you’re
blowing off more CO2.
And CO2 is the
stimulus to breathe.
And so if you have
less CO2 around,
you’d be able to hold your
breath for a longer of time.
However, it’s not recommended when
you’re doing breath hold-diving
because of that blackout
type of phenomenon.
What other things affect
breath hold time?
One is what you’re doing
underneath the water.
So if you’re doing something like
snorkling or taking pictures,
the amount of energy
you expend underneath
the water will affect
your breath hold time.
Also, how much O2 you have in
your lungs before you start.
Finally, there’s a number of other items
associated with psychological factors
as well as some task and focus diversions
that will increase your breath hold time.
For example, if you’re
diving off a coral reef
and see a very pretty fish or
trying to look at something,
if you’re task is focused
on that particular fish,
you can hold your breath
a little bit longer
than you can if you were thinking about
needing to come up to the surface to breathe.
There are some chronic benefits
of breath hold-diving.
These include things like increasing
in some pulmonary function values
such as total lung capacity, vital
capacity and inspiratory capacity.
There’s also blunting or decrease
sensitivity to carbon dioxide and oxygen.
And what this does is make sure that
you don’t have to breathe as often
because you can hold
your breath for a longer
period of time before the
stimulus to breathe hits.
And there may even be some adaptation
with things like diving bradycardia
and some heightened peripheral
vasoconstriction that sometimes happens.
Now, that we’ve covered increases
in barometric pressure,
let’s go to decreases
in barometric pressure.
So usually the idea of decrease
in barometric pressure is
when a person goes to altitude or
to high mountain environments.
This particular diagram shows you
that in terms of barometric
pressures along the Y axis,
these are the changes that occur as
you increase height or elevation.
I’ll point out a couple to you such
as the summit of Mount Everest.
There’s also places like
Denver or Mexico City.
So there are some of these areas
that people live for full time
throughout the whole year and other
ones that you just might visit once.