00:01
So the final influence
is going to be
what we know as
ventilation perfusion coupling.
00:08
So just a couple
of vocabulary words
when we say perfusion.
00:12
We're referring to
the blood flow
that is reaching the alveoli.
00:17
When we refer to ventilation,
we're talking about the gas flow
or the amount of gas
that is reaching the alveoli.
00:25
So for optimal
efficient gas exchange,
we want our ventilation
and our perfusion rates
to be equal to each other.
00:36
These are going to be regulated
by auto-regulatory
mechanisms in the body.
00:42
When we look at our partial
pressure of oxygen.
00:45
This is going to actually
control
perfusion by changing
the diameter of our arterioles.
00:54
We look at the partial pressure
of carbon dioxide.
00:57
This is actually going
to control ventilation
and it's going to do this
by changing the diameter
of our bronchioles.
01:07
So changes in the partial
pressure of oxygen
as I said before,
is going to lead to changes
in the diameter of arterioles.
01:16
When our alveolar
oxygen is high.
01:19
So we have a high partial
pressure of oxygen.
01:22
This is going to cause
the arterioles to dilate.
01:26
But when the alveolar oxygen
levels are lower
the arterioles are going to constrict.
01:34
This constriction
of the arterioles
is then going to direct
blood away from the alveoli
that have low oxygen
toward alveoli that have
a higher oxygen load.
01:45
So that the blood
can pick up more oxygen.
01:49
This is an interesting
phenomenon because it
is opposite of what we see
and our systemic arterioles.
01:56
So in our systemic arterioles,
we dialate our arterioles
when our oxygen levels are low
in order to get more oxygen
and we constrict them
when our oxygen levels
are high or adequate.
02:12
So changes and our partial
pressure of carbon dioxide
in our alveoli,
are going to affect the diameter
of our bronchioles.
02:20
So it is going to have
more of an effect on ventilation.
02:25
When our alveolar carbon
dioxide levels are high
we dilate are bronchioles
in order to allow
for more exhalation
of the carbon dioxide.
02:35
But when our
alveolar concentrations
of carbon dioxide are low
we're going to constrict.
02:41
The bronchioles.
02:45
The dilation again
of these bronchioles.
02:48
It's what's going to allow
for more elimination
of our carbon dioxide.
02:55
So changes in the diameters
of our local arterioles
and bronchioles
are what we refer
to as ventilation perfusion.
03:04
So this ventilation perfusion
is never going to be balanced
across all of our alveoli.
03:10
And the reason why is
because our alveoli
themselves are never balanced.
03:15
There are regional variations
between the alveoli
due to things such as
the effect of gravity
on blood and air flow.
03:25
Also sometimes
are alveolar ducts
can become plugged
and therefore those alveoli
are not ventilated
or have very low oxygen.
03:34
And because of that we do not
want our blood going to these
and adequately
oxygenated alveoli
and so we divert
the blood to other
alveoli that are
more well-ventilated.
03:49
So, let's see what happens
when we have a mismatching
of ventilation and perfusion.
03:55
So and areas were ventilation
is lower
than perfusion or
when there is a local hypoxia,
and there's less oxygen
in an alveoli.
04:06
We are going to
constrict the arterioles
so that we divert perfusion away
from this local hypoxia
to areas of the lungs
that have adequate oxygen amounts.
04:20
We are going to do this
until we match
the ventilation and perfusion.
04:27
The opposite occurs
when our ventilation
is greater than perfusion
and we have a higher
than normal level of oxygen.
04:36
In this case instead
of constricting arterioles
and diverting blood away,
we're going to
dilate the arterioles
so that we can adequately
you get more blood to
get some of this oxygen
out of the alveoli
into the blood.
04:53
And we do this until again
we match ventilation
and perfusion.