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.
The lecture Effects of Pulmonary Artery Pressure – Pulmonary Blood Flow by Thad Wilson, PhD is from the course Respiratory Physiology.
If mean pulmonary vascular pressure increases, what is the corresponding effect on pulmonary vascular resistance?
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