00:01
So as I said before,
our respiration rates
are going to be affected
by multiple factors
including chemical factors.
00:08
The influence of
higher brain centers,
pulmonary irritant reflexes
and also inflation reflexes.
00:16
So, let's take a closer look
at some of these things.
00:20
So the chemical factors
are going to be the most
important of all the factors
that are going to
affect our depth
and rate of inspiration.
00:29
The partial pressures
of carbon dioxide
oxygen, as well as our
H+ concentrations are pH
are going to be the most important
of these chemical factors.
00:41
Levels of these
chemicals are sensed
by central chemoreceptors
found in the brain stem
as well as peripheral
chemoreceptors
found in the aortic arch
and the carotid arteries.
00:55
So taking a closer look at
these peripheral chemoreceptors.
00:59
We find that sensory nerve
fibers and cranial nerve lX
or the pharyngeal branch
of the glossopharyngeal
cranial nerve
are going to send impulses
to the carotid bodies
found on the carotid arteries.
01:15
From their central nerve
fibers in the cranial nerve X
are the vagus nerve
are going to send signals
to the aortic bodies
found in the aortic
arch of the heart.
01:28
So other influences
are going to be
things like the partial
pressure of carbon dioxide.
01:35
So this is the most potent
and closely controlled.
01:39
If our partial pressure
of carbon dioxide levels
rise or go up,
which is known as hypercapnia.
01:47
The carbon dioxide will
accumulate in our brain
and join with water to
become carbonic acid,
and the carbonic acid
will then dissociate
leasing the H+
and causing a drop in our
pH or increased acidity.
02:05
Increase H+ stimulates
the central chemoreceptors
of the brain stem
which will then synapse
with the respiratory regulatory
centers that we talked about.
02:17
The respiratory centers
will increase depth
and rate of breathing
which will act to lower
our partial pressure
of carbon dioxide
by getting us to exhale
more carbon dioxide
and this will
cause our pH levels
to rise back to normal levels.
02:37
If blood partial pressure of
carbon dioxide levels decreases.
02:41
Our respiration will
become slow and shallow.
02:45
Also apnea or when
you stop breathing
or breathing cessation may occur
when our carbon dioxide
levels are extremely low.
02:57
Sometimes swimmers take
advantage of this phenomena
and voluntarily hyperventilate
in order to enable them to
hold their breath longer
this works because as
they hyperventilate
it causes their carbon
dioxide levels to drop
because they're exhaling
a lot more carbon dioxide
than they're inhaling oxygen.
03:19
This causes a delay
in respiration
as the carbon dioxide levels
need to build back up.
03:26
And so while they're
holding their breath,
they're able to hold it longer
because their body wants to
hold in more carbon dioxide.
03:36
However, by doing this
they are counteracting
the the need their body
has four oxygen levels.
03:43
So this is still a
dangerous practice to do.
03:48
So the changes in our partial
pressure of carbon dioxide
can regulate ventilation by a
negative feedback mechanism.
03:57
So let's just take a look
at how this negative
feedback works.
04:02
First,
let's start with a stimulus
if that stimulus
is the partial pressure
of carbon dioxide
decreasing the pH in the
brains extracellular fluid,
then the central
chemoreceptors in the brain
are going to respond
to that lower pH.
04:21
As well are peripheral
chemoreceptors
found in our carotid
and aortic bodies
can also be stimulated
when there is a
decrease in the pH.
04:33
Both of these stimuli
are going to send impulses
to our medullary
respiratory centers.
04:41
The medullary respiratory
centers then send impulses
to the respiratory muscles
in our thoracic cavity
and this is going
to cause ventilation
or more carbon
dioxide to be exhaled.
04:55
So we already had too
much acid or too much H+.
05:00
And so we need to get
rid of carbon dioxide
so we can shift that
reaction away from H+.
05:09
And once this happens,
the arterial partial pressure
of carbon dioxide and the pH
will return back to normal.
05:20
So hyperventilation
is when we increase the depth
and the rate of breathing
and it exceeds our bodies need
to remove carbon dioxide.
05:30
So we're breathing out so much
that we're actually
losing more carbon dioxide
than our body should.
05:39
Usually hyperventilation
can be caused
by anxiety attacks.
05:43
Although there are other reasons
why you might hyperventilate.
05:47
This hyperventilation
leads to a decrease
in our bloods
carbon dioxide levels
known as hypocapnia.
05:55
Hypocapnia can lead to
cerebral vasoconstriction,
which can lead to ischemia
which can result in
dizziness and
sometimes fainting.
06:06
Usually you are able to know
when your blood CO2 levels
are starting to drop
because the early symptoms
include things like the tingling
and involuntary muscle spasms
in your hands and in your face.
06:20
The way we treat
hyperventilation
is by getting people
to breathe into a bag.
06:26
So if a person is having
an anxiety or panic attack
and they're hyperventilating
and removing too
much carbon dioxide,
we get them to
breathe into a bag
and by doing this,
we're going to
have them inhaling
some of that carbon dioxide
back into their body
thus increasing our
carbon dioxide levels
and getting us back
to normal CO2 levels.
06:54
So not only does CO2
or the partial pressure
of CO2 have an effect
but also the partial pressure
of oxygen can have an effect.
07:04
Peripheral chemoreceptors
and our aortic
and carotid bodies can sense
arterial oxygen levels.
07:12
If the partial pressure of
oxygen begins to decline
there's only a slight
effect on ventilation
because we have huge
reservoirs of oxygen available
in our hemoglobin.
07:26
It's going to require
pretty substantial drop
in arterial partial
pressure of oxygen
in order to increase
ventilation.
07:35
So you would have to get
really low oxygen levels
in order for our body to respond
by trying to breathe more.
07:44
When excited, the chemoreceptors
will then cause the
respiratory centers
and our medullary and pontine
areas to increase ventilation,
but this again only happens
when we drop really low.
08:01
So pH is another factor
that influences our rate
and depth of breathing
and pH can modify
respiratory rate and rhythm
even if the carbon dioxide and
the oxygen levels are normal.
08:15
This is going to be mediated by
those peripheral chemoreceptors
in the carotid
and aortic bodies.
08:22
And a decrease in the
pH can either reflect
too much carbon dioxide in the
body or carbon dioxide retention,
but it can also reflect things
an accumulation of lactic acid
after a particularly
anaerobic exercise activity
like sprinting or
lifting weights
as well as excess ketone bodies,
which are lot of
times are acidic
this can happen when
people go on diets
like a keto diet,
where they're taking
in more protein,
beans and fats and
less carbohydrates
and so their body
switches to ketosis.
08:59
The respiratory center
can control attempts
to raise the ph
by increasing the
respiratory rate and depth.
09:07
So if the pH drops too low,
then the body can control
by a causing you to exhale
or breathe in and
out a lot more often.
09:21
So to summarize
because we've gone
through a lot of these
different factors.
09:27
Rising carbon dioxide levels
are a powerful
respiratory stimulant
when the carbon dioxide levels
go up or down
our body is going to respond.
09:40
Normally our blood oxygen levels
are going to affect breathing
but only indirectly
by influencing
peripheral chemoreceptors
and sensitivity to changes
in the partial pressure
of carbon dioxide.
09:56
If our arterial oxygen levels
fall below a
threshold of about 60.
10:03
That is when the partial
pressure of oxygen
will now become a major
stimulus for respiration
by way of those
peripheral chemoreceptors.
10:14
When we have changes
in our arterial pH,
this can also affect
our respiratory rate
by resulting from
carbon dioxide retention
or metabolic factors,
like something we ate
or some type of disease
and by this we're going to
try to adjust our bloods pH
by adjusting how
much carbon dioxide
is coming in and
out of the body.
10:38
This too is also
going to be influence
by those peripheral
chemoreceptors.