Health and medicine
- Arteries vs. veins - what's the difference?
- Arteries, arterioles, venules, and veins
- Layers of a blood vessel
- Three types of capillaries
- Pre-capillary sphincters
- Compliance and elastance
- Bernoulli's equation of total energy
- Stored elastic energy in large and middle sized arteries
- Compliance - decreased blood pressure
- Compliance - increased blood flow
Find out how compliance allows arteries to store elastic energy (and lower pressure). Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
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- So, when feeling the pulse, one is actualy feeling the enlargement of the vessels, as systole pressured blood passes through them?(6 votes)
- Yes, but remember the energy pulse itself moves much faster than blood and that's why you can feel almost instantaneously the beat of the heart, located in the thoracic cavity, at the radial or ulnar artery that pass in the wrist.(7 votes)
- The above scenario will match a person manifesting arteriolar sclerosis and arteriosclerosis together (which is the actual case in most of the hypertensive patients)..But in the above scenario,as KhanAcademy was referring to arteriosclerosis(Aorta/Any artery in general)
the increase in DBP does not fit right with the explanation
Here's Why:::>>>The diastolic blood pressure in a non compliant vessel or a low compliant vessel falls lower than normal due to windkessel effect.The above example showing 160/100 for the non compliant scenario should have been 160/76 or 160/78.(less then 80)..?(5 votes)
- I agree with the above observation that non compliant vessel will have lower diastolic blood pressure. The way I understand this is that in the absence of elastic energy, the forward movement will be at the cost of pressure energy and hence will lead to lower diastolic pressure.(5 votes)
- At9:47, Rishi says that there is no movement in the aorta of a non-compliant person in diastole. How is there pressure if there's no movement?(3 votes)
- There is pressure within a balloon even if there is not further expansion. It is opposed by the tendency for the balloon material to contract to regain its resting shape/size. You can see this if you pop the balloon. The same principle is at play here.(5 votes)
- Actually this pressure wave moves much faster than the blood itself! Can anyone please explain the physical reason behind this phenomenon?(3 votes)
- In non-compliant systole, how does the movement energy still exist? This stuff confusing me since dr. Desai said that the elastic energy not only make the pressure lower, but also helps the converting process. If the elastic energy is absent, where does the movement energy come from?(3 votes)
- Why isn't this all being modeled with the flexible vessels, arterial and venous, shown as capacitors, and the whole thing layed out on a timing grid?(2 votes)
All right, I'm going to compare two individuals. One individual with very compliant blood vessels, and that person is going to be, as a result of the fact that they're compliant, they're going to be very happy. And then one person with very non-compliant vessels. And that person will be sad. And we also have two parts of the heart cycle. We have systole and diastole. So we're going to do it both for systole and diastole. This is systole, and we'll do it for diastole. And I'll write it out again, because I want to make sure we see clearly the difference between someone with compliant blood vessels and someone with non-compliant. Remember, non-compliant basically means having stiff blood vessels. And the processes that cause this are things like arteriosclerosis for the large vessels or arteriolosclerosis for the smaller vessels. And let's divide it out with a large line. So let's imagine that we have now, for our first person who has compliant blood vessels in systole. What will that look like? So let's say you have your heart here. And I'm going to stretch out the aorta. So it doesn't normally look this way. But I'm just going to show you what it would look like in a person that has the ability to have nice, flexible arteries. It would look something like that. And the same region of the heart and blood vessels in someone with non-compliant arteries would look like this. So again, this is right when the heart is squeezing blood out. So we know that blood is flowing through here. And in fact, just to highlight the fact that this person has very stiff vessels, let me show you kind of these atherosclerotic plaques sitting inside of their arteries, making them stiff. So really, they're unable to be flexible. They're not ballooning out. And let me show you what the vessel kind of would look like, just so you can see how ballooned out this person's blood vessels really are here. So this is that inner dimension of the vessel. This is what would look like if they didn't balloon out. But in fact, they did. So let's take a point, maybe there and there. And let's call that the spot where we're checking pressure energy. And I'm going to talk in terms of energy. And this is where we're actually detecting pressure energy, let's say. And this bar represents how much energy we actually see. So this is a representation of how much pressure energy is at that spot. And let's assume that, even though we know that the vessels are different in these two people, that their hearts are the same, that they're working equally hard, and putting equally a similar amount of energy into the blood vessels. So we know that the pressure energy should be quite similar between the two, from the heart's standpoint. And we also know that blood is moving out. So we actually can look at movement energy as well. And I'm going to draw that as a bar also. We've got movement energy here in yellow and pressure energy in purple. And as you look at this, you're going to see that the movement energy, I'm going to assume for the two cases, is similar. So similar-sized bar. And actually, in people with atherosclerosis, they have compensation, so these bars actually start looking a little different. But just for right now, let's imagine that we're just taking a snapshot the moment after these vessels became hard. So that's the movement energy, and I'll just label it movement. And in purple is the pressure energy. And what I want you to notice is that I haven't addressed a very important point, which is that this is ballooned out. And so we know that, just like in a balloon or a rubber band, if you stretch it out, you're going to actually start getting some extra energy. And we call that elastic energy. And that elastic energy would be something like that. It would actually take up a chunk of that pressure energy. Because it's the pressure in the blood that's actually causing the vessels to balloon out. So this is the elastic energy, which just took a chunk of that pressure energy away. And what's left is the leftover pressure energy. And we have really no ballooning on this side. So really it's all pressure energy. So if I was to actually try to measure how much energy, and obviously, I don't measure movement energy or elastic energy. The only thing I really measure in the doctor's office is the pressure energy. And I say, hey, your pressure was so-and-so. So let's give some numbers just so we can keep all this straight. This person might have a blood pressure, let's say 160. And the person who's happy with compliant vessels might have a blood pressure of 120. And we can see exactly why, because some of that energy got taken away and stored away as elastic energy. So, so far, so good. You can already see how elastic energy is really helpful, because it helped you lower the pressure. Now what happens in diastole? So now, the heart is resting. The heart is taking a quick breather to refill. And the vessels are now a little bit less full of blood, because a lot of that blood has already left and gone on to the foot and the face and all of the different parts of the body. And this is what the inside of the vessel looks like again, just to keep that straight in our heads. And on this non-compliant person's vessels, they actually look basically the same. It's not going to look any different. And you've got your atherosclerosis. That didn't go away. Because this is all just looking at two different parts of the heartbeat, the resting and the active part of the heartbeat. So none of that goes away. And so let's say I do the same experiment, where I look at this purple x, and I take a look at how much pressure energy there is. Now I know there's going to be less than before. I know that because the heart is taking a break. And so this is all just whatever's residual, whatever's left over from systole. I've got a little bar of purple there. And let's say that the bar is about the same height here. And I've got some pressure energy here as well. And already you can see that the lesson from the first part of this picture was that we have a little bit of elastic energy here. And you can see that. Otherwise, the two vessels would look the same. But you can see there are still some areas where it's a little stretched out. So let's draw that in here. A little bit of elastic energy left. It's not completely gone. This is my elastic energy. And already, you can see that that means that, of course, in diastole, my pressure is going to fall as well. So I've got lower pressures in diastole, just like we did in systole. This is my non-compliant diastolic blood pressure. And I would even throw some numbers. I could say this is maybe, let's say 100, and up here, maybe 80. Because it's got to be a little bit lower, right? Now notice this. This is actually really, really interesting. Notice this. Notice this elastic energy here. And is it the same as the amount here? Well, the answer is obviously no. It's not the same. There's less. And so the other cool feature about elastic energy is not only does it lower your pressure, which we've talked about, but it also can be used to convert it into movement energy. So isn't that interesting? You can actually use this stored elastic energy-- let's say that's the difference. I'm just trying to eyeball it. But let's say this is the difference. You can actually use this to move blood. You can actually use this for movement energy. And so you can see that this actually adds up. You can see that the elastic energy before is about the same as the elastic energy afterwards plus the movement energy. So there are two important points here. One is that the elastic energy helps lower the pressure. We saw that here and here. And two is that it actually helps you generate movement of blood. And so you can actually, now in diastole, move some blood forward. And that's because the elastic energy is recoiling, just like a rubber band recoils, and that energy has to go somewhere. And it's going into moving some blood forward. So it's taking a little bit of blood and saying, OK, move forward a little bit. And you actually don't have that phenomenon, or that interesting, cool property is not really happening down here. So you don't have any of that on the non-compliant side. So these are the things I wanted to kind of point out to you, and show you why it's so important to have flexible arteries.