00:00
Now the other factor that
dramatically affects blood flow
increases pulmonary blood flow through both
a recruitment and a distension mechanism.
00:04
through the lungs is the
lung volume itself.
00:10
So lung volume can be thought
of as how inflated the lung is
versus how much you’ve
been able to breathe out.
00:17
So if we plot pulmonary vascular
resistance over lung volume.
00:22
With low lung volume being on
the left hand side of the graph
and high lung volume being on
the ride hand side of graph
and those are denoted as RV or
residual volume at low lung volume.
00:35
And TLC or total lung
capacity at high lung volume.
00:39
There is an effect of
compressing the capillaries.
00:45
So as you compress capillaries,
you get an increase in
resistance at high lung volumes.
00:52
Oppositely, in terms of the
blood vessels themselves,
as you go to a low lung volume,
there is an increase in
pulmonary vascular resistance.
01:07
So we have two different factors
that are affecting here.
01:11
One having high resistances at low
lung volume and then coming down
and the other is having high
resistance at high lung volumes.
01:23
This yields a total pulmonary
vascular resistance
in this kind of a
U shaped curve.
01:32
That means that at a
moderate lung volume,
the resistance through the lungs, in
terms of the blood flow, is lowest.
01:41
While you’re at a low lung volume,
you have high resistance.
01:45
And at high lung volume, you have high
resistance to pulmonary blood flow.
01:49
Okay. So how in the
world do these happen?
Let’s first take the compression
effect and discuss that.
01:55
And then we'll discuss the mechanism
behind the supply vessel dilation effect.
02:01
So if we look at the compression effect
and that’s denoted here as low
lung volumes, low resistance,
high lung volumes,
high resistance.
02:12
You can see on this graph in the slide here
where we have capillaries denoted as red.
02:19
And the alveoli as a kind
of hexagon white shape.
02:23
As you inflate those alveoli,
you can notice that they will
squeeze out some of the red
and this is compressing these
pulmonary capillaries.
02:36
You might think that
seems very odd that the
capillaries can be compressed
such as like this.
02:43
However, you should
think of there is low
blood pressure in the
pulmonary vasculature.
02:49
So factors such as inflating these air sacs
can actually increase the
resistance of flow through that
as there’s no longer as
large of a luminal diameter.
03:01
So that is the
compression effect.
03:03
Inflate the air sacs,
you have more resistance than
you did at low lung volumes.
03:10
Now, if you look at the
vessel dilation effect, for this,
we need to remember that the
blood flow supply is surrounded
by not only alveoli, but also
other connective tissue.
03:22
And what you can do is pull
on this connective tissue
by creating a negative pressure.
03:28
And we call that a negative
pleural pressure or P sub PL,
At this point, you have all the air sacs
pulling on that particular blood vessel.
03:41
And what happens is it makes
that blood vessel wider
or have a larger luminal diameter.
03:47
And in that case, it would
decrease its pressure.
03:51
And as you decrease the
pressure then, you’d have more
flow through that area
because of lower resistance.
03:57
And so that denotes the low lung
volume, having higher resistance,
and high lung volumes, having lower
resistance to pulmonary blood flow.
04:07
Putting all these together,
it gives us that U shape
of pulmonary blood flow to
pulmonary vascular resistance
in terms of the
lung volume effect.