This is a graph that looks at
pulmonary vascular resistance,
which is the resistance of blood
flow through the tubes of the lung.
And then we’re comparing that to
mean pulmonary artery pressure.
So this is the pressure pushing
the blood through those tubes.
And this forms a very
in which at low pulmonary artery
pressures, resistance is high.
But as pulmonary artery
you actually get a decrease in
pulmonary vascular resistance.
And this is fairly unique.
So as pressure goes up, you have
lowering of the resistance.
What does this do for blood
flow is as pulmonary blood flow
increases as pulmonary
artery pressure increases.
So then they are more linearly
related in a positive manner.
This is a very
It means that it’s not governed in the
same way as your systemic vasculature,
that will be covered in the
So this brings up a very
unique point of view
and that is we have from
the previous slide,
an increase in pulmonary
And as pressure increases, the pulmonary
vascular resistance decreases.
So what that meant was as
pulmonary artery increased,
blood flow also increased.
How does this happen?
Well, it seems to occur
via two mechanisms.
And let me go through
what those are.
The first is going to be a recruitment
and the second is a distension issue.
But let’s kind of walk
through these step by step.
In normal pulmonary vasculature,
some of the blood vessels are collapsed
even during the rested state.
There are some of the blood
vessels that are not collapsed,
but yet the blood is not
moving very rapidly
So both of those items have
low blood flow through them.
There are some of the capillaries
though, just as you would expect,
are open and do conduct blood.
So there’s a little bit
of a notion here that you
only get blood flow through
some of the capillaries.
Other parts of the
capillaries are collapsed
and some have just
low blood flow.
As pressure though increases,
what you get is an opening
of these blood vessels.
First the ones that were
previously collapsed start to open
and the ones that were not
conducting flow through very rapidly
as the pressure increases, those are
pushed through to a much greater extent.
The ones that had had
normal blood flow,
And so that is the distension component
versus the recruitment component.
So we have recruitment that occurs through
the previously collapsed blood vessels.
We had distension that occurred
through the blood vessels
that were already open
that became wider.
Therefore, we have an end result
of an increase in perfusion or blood
flow through the entire lung.
So this is how the process of
increasing pulmonary artery pressure
increases pulmonary blood flow through both
a recruitment and a distension mechanism.