Effects of Pulmonary Artery Pressure – Pulmonary Blood Flow

00:02 This is a graph that looks at pulmonary vascular resistance, which is the resistance of blood flow through the tubes of the lung.

00:08 And then we’re comparing that to mean pulmonary artery pressure.

00:13 So this is the pressure pushing the blood through those tubes.

00:18 And this forms a very unique relationship in which at low pulmonary artery pressures, resistance is high.

00:25 But as pulmonary artery pressure increases, you actually get a decrease in pulmonary vascular resistance.

00:33 And this is fairly unique.

00:34 So as pressure goes up, you have lowering of the resistance.

00:40 What does this do for blood flow is as pulmonary blood flow increases as pulmonary artery pressure increases.

00:49 So then they are more linearly related in a positive manner.

00:52 This is a very interesting process.

00:56 It means that it’s not governed in the same way as your systemic vasculature, that will be covered in the cardiovascular section.

01:03 So this brings up a very unique point of view and that is we have from the previous slide, an increase in pulmonary artery pressure.

01:12 And as pressure increases, the pulmonary vascular resistance decreases.

01:18 So what that meant was as pulmonary artery increased, blood flow also increased.

01:24 How does this happen? Well, it seems to occur via two mechanisms.

01:30 And let me go through what those are.

01:32 The first is going to be a recruitment and the second is a distension issue.

01:37 But let’s kind of walk through these step by step.

01:39 In normal pulmonary vasculature, some of the blood vessels are collapsed even during the rested state.

01:47 There are some of the blood vessels that are not collapsed, but yet the blood is not moving very rapidly through those particular capillaries.

01:59 So both of those items have low blood flow through them.

02:05 There are some of the capillaries though, just as you would expect, are open and do conduct blood.

02:11 So there’s a little bit of a notion here that you only get blood flow through some of the capillaries.

02:17 Other parts of the capillaries are collapsed and some have just low blood flow.

02:24 As pressure though increases, what you get is an opening of these blood vessels.

02:30 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.

02:46 The ones that had had normal blood flow, widen.

02:51 And so that is the distension component versus the recruitment component.

02:56 So we have recruitment that occurs through the previously collapsed blood vessels.

03:02 We had distension that occurred through the blood vessels that were already open that became wider.

03:09 Therefore, we have an end result of an increase in perfusion or blood flow through the entire lung.

03:16 So this is how the process of increasing pulmonary artery pressure increases pulmonary blood flow through both a recruitment and a distension mechanism.