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Pressure in the left heart - part 1

Watch the pressure in the left heart go up and down with every heart beat! Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.

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  • piceratops seedling style avatar for user http://facebookid.khanacademy.org/1529980964
    Hi at around of the video you discuss the closing of the Valves. When you say that the closing of the valves cause the sound, is that the actual closing of the flaps or is it the blood hitting the valves?
    I am slightly unsure about which is right.
    (8 votes)
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    • aqualine ultimate style avatar for user invictahog
      The valves close silently - this has been proven using echophonocardiography. The first heart sound is related to the closure of the tricuspid and mitral valves. After they close, the blood begins to press against them and they bow slightly into the atrium. They reach their maximum elastic point and then begin to spring backwards against the blood. This sets up vibrations in the heart wall and the blood itself that is heard as S1. S2 is associated with the closure of the aortic and pulmonic valves. They also close silently and the noise is made by the vibrations set up within the vessel and the blood itself by the impulse of the blood striking the closed valve.
      (12 votes)
  • blobby green style avatar for user tara
    How did blood flow to a dinosaur's brain? maybe in the Sauroposeidon's brain? What experiment can I do to help me understand that?
    (5 votes)
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    • blobby green style avatar for user kaoutar
      the problem in understanding the physiology of the circulation of blood in dinosaurs is that their actual anatomy is not certainly established... there are some proof that the ''Thescelosaurus'' particularly could have had a certain cardiac stucture wich looked like a four chambered heart and coming out of it and going posteriorly a vessel that is similar to aorta...
      so assuming that a dinosaur has a cardiac circulation that is slightly similar to ours...: since the problem in the lenght of it neck and the fact that the blood flow must be opposite to gravity in direction...
      the systolic pressure will be much more important which can be due to a more important ventricular muscle,
      the carotide artery which brings the blood to the head and neck ( in our context) is the first branch that leaves the left ventrical, so it gets loaded the first... in order to enhance it's flow it could have a larger diameter in dinosaurs (resistance decreases),
      again the problem in order to explain how does blood get to the dinosaur's brain, we need to have a clear idea about its anatomy first:)
      i hope it was helpful:)
      (9 votes)
  • duskpin tree style avatar for user TheFlyingScotsman
    So, can I imagine the left heart to be like a bag with two holes, with blood flowing in such a way that :
    (1) the 'in' hole (mitral valve) is open, the 'out' hole (aortic valve) is shut
    (2) the bag gets filled (with blood)
    (3) the 'in' hole shuts
    (4) the 'out' hole opens (blood flows out)
    (and the process is repeated)

    Did I get it right?
    (4 votes)
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    • blobby green style avatar for user kaoutar
      the phenomenon is a little more complicated than what you just described:) this videos are talking about the particular changes in the pressure of the left ventricules, we could do the very same thing to study all the other 3 chambers: (if you could bear with me:))
      - first, you need to see the function of the heart in a gross manner then you could focus on each cavity and study it isolated.
      *the first important concept when you look at the heart as a hole, is that it can be devided into two functional parts: a left heart (left atrium and ventrical) and a right heart (left atrium and ventrical)
      -> the right heart :the atrium receives the blood coming from the veinous circulation ( wich contains waste product: CO2) throught the superior vena cava for the superior part of the body, inferior vena cava for the inferior part of the body (simplifying:)) ,the blood in squeezed into the right ventrical throught the tricuspide valve wich ejects it throught the pulmonary valve and pulmonary artery to the lungs. So: the right heart gets the veinous blood, pomps it to the lungs...:)
      -> the left heart: the left atrium receives the blood from the lungs, (which has got O2) , pomps i throught the mitral valve to the ventrical which ejects throught the aortic valve to the body: so the left heart pomps the oxygenated blood to the body.
      --> the two systems are parallel: as you can imagine desoxygenated blood comes to the right atr, to the right ventricals to the lungs, to the left atrium to the left ventrical to the body and the cycle repeats itself...ps: there are no valves between right atrium and both the vena cava, and the left atrium and the pulmonary veins.
      *then once you've known that, the second concept would be that: there are two phenomemons that control the heart activity: the electic phenomenons (related to the excitable tissu of the heart: studied by EKG), the mecanical phenominons (due to the changes in pressure studied by the heart sounds and pressure measurments).
      these are like the very ABC that you need to know before going any deeper in studying cardiac physiology... in order to imagine those i used to draw schemes that are rather primitive but helpful:)
      i hope that was clear enough:)
      (6 votes)
  • winston baby style avatar for user Ali Arshad
    How does the resistance in Aorta keeps the pressure high ?
    (3 votes)
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    • hopper cool style avatar for user SofiyaMarkova
      resistance builds up the pressure as the fluid is not allowed to move through even though it has the energy to. pressure is a force on something by something else in contact with it. keeping the resistance high and not letting the blood move through makes the blood push on the walls of the Aorta, making a high pressure until the resistance is released and the blood rushes with a high pressure as all that built up force and energy can be released
      (2 votes)
  • leaf yellow style avatar for user Salsabeel Abu Aisheh
    at if the aoratic pressure stays high , why he draw the line towards down ?
    (3 votes)
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    • hopper cool style avatar for user SofiyaMarkova
      the pressure is high and since the blood under high pressure continues to find a place to go and there is an opening to go back (going forward is harder because of the resistance from blood vessels) some of it goes back through where it came from.

      analogy: when there is a crowded bus and more people want to go in while fewer people are slowly going out from another door. it is hard to get into the bus as there is resistance from having less room for people to go in. this leads to some people who are trying to go in to step back/ fall out of the bus as they don't have anywhere further to go in and get pushed back from where they came from as there is more space and less pressure outside of the bus.
      (2 votes)
  • blobby green style avatar for user jessica.sax94
    So does the ventricle contract all of the blood out of that chamber or does some of it get left behind after the semilunar valve close?
    (3 votes)
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    • blobby green style avatar for user J fx
      There is always some residual volume left in a chamber after a contraction this is known as ejection fraction which is a measure of the initial volume at the beginning of the contraction divided by the residual volume after the contraction. A typical value is ~60%.
      (2 votes)
  • blobby green style avatar for user ajmiyabeevim
    Could you plz explain the branches and rebranches of aorta?!😊
    (2 votes)
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Video transcript

So you're pretty familiar with this image of the heart. We have the four chambers. And I'm just going to start by labeling them-- the right atrium and right ventricle on this side and the left atrium and left ventricle on this side. And the question is this. What happens if we choose two spots? I'm going to choose this one right here, with the little x in left ventricle and some other spot over here in the aorta, let's say, with the purple x. And this is, of course, our aorta up here. What happens if I follow the pressure at those two spots? So of course, I was going to say maybe if I'm the red blood cell sitting there, but we know red blood cells move around. But let's say I'm just following the pressure at those two spots, those locations, over time. So this will be time over here. What does the pressure look like at that location? And let's say I'm following for, let's say, one second. So, if my heart rate was somewhere like 60 beats a minute, that would basically mean one second would be one beat. This is 60 beats a minute. And just keep in mind, 60 beats a minute is actually pretty low. So that would be like if I'm reading a book or sitting around relaxing. And on this side, let's do pressure. And I'll do 0 to, let's say, 100 up here. And remember, the units of pressure are millimeters of mercury. Now actually, before I start, let me even jump into some naming, just so we don't have to stop later. These are the valves. This is the mitral valve. And below it, I've drawn the tricuspid valve. And put together, we would call these the AtrioVentricular valves. This is the AtrioVentricular valves. And AtrioVentricular, I've capitalized A and V because sometimes you'll see the word AV valves. AtrioVentricular valves are also known as AV valves. And the other two valves, here, this is the pulmonary valve down here. And on the other side of it right here is the aortic valve. Put together, we would call these the semilunar valves. And actually, semilunar, you might think of it as like a half moon. But there's no shorthand for that, usually. So people just call them the semilunar valves. So what does the pressure tracing look like at my yellow x? Let's go back to that question. So I'll start out here on the axis. So it starts out really low. Left ventricular pressure is surprisingly low most of the time. And you'll actually see that now when I draw it out. You know, I always think of it as this chamber that's cranking and pushing and high pressure. And that's true. There is some of the points along the way when the pressure gets very high. But for most of the time, it's actually pretty low. And it creeps along, goes up very slowly. Well, why is it going up at all? That's the first question. Why doesn't it just stay steady? Whatever pressure it is, why is it going up? Well, it's going up because there's actually flow here through the mitral valve. So blood is going into the left ventricle initially, and when there's more blood in that chamber, over time, the pressure slowly builds up. Just like if I'm pouring water into a water balloon, over time, every little bit more water I put in there, the pressure in the balloon goes up. So, that's why it's creeping up. And then you get to a point where all of the sudden, there's a muscle contraction. So you have a depolarization wave that comes through, and all of this heart muscle is cranking, just pushing in. And of course, simultaneously, the right ventricle is doing the exact same thing. So all of the things that I'm saying for the left ventricle, for the most part apply also on the other side. So they're contracting. And the left ventricle contracts hard, and the pressure begins to rise. Now just right there, just right where it begins to rise, you might say, well, what did you even do? And at that moment where I drew a slight increase, a tiny little increase-- you can see it if you squint your eyes-- at that moment, this valve closes. Why? Because at that moment, at that very moment, there is a little bit of push back here. And the slightest bit of push back makes the valve shut. So once the pressure on the left ventricle side is greater than the pressure on the left atrium side, the valve shuts. And so the valve closes at that point. And then you have a rise, a rapid rise, in the left ventricular pressure. And it goes up, up, up, like that. So let me just write that down since I just said it. The AV valves close. And that's a new thing, because they were open. So let me box that. AV valves close. And the semilunar valves, the other ones, they stay open. Semilunar stays open-- nothing new there. Actually, sorry, I said open, and I'm even writing open. But I mean close. Sorry. So let me not confuse you and just change that right now. Semilunar valves stay shut. And to drive home that message, I'll even put a block there. So they're still shut. So all the valves at this point are now closed. And that might be news to you. You might have thought, well, I thought at some point, some valves were always open. And that's not true. At this point, both valves are closed. And the left ventricle is basically squeezing. But the blood has really nowhere to go. It's just sitting in a trapped room, and the pressure is rising and rising fast. And then at some point, it gets to a spot where an interesting thing occurs. So let me actually draw that here. Let me erase this slightly. Let's draw the aortic pressure. So the aortic pressure, let's say, is something like this. And it's drifting down. Well, why is aortic pressure drifting down? Well, it's because in the aorta, blood is rushing away. Remember, from the previous squeeze, you've got blood rushing away, out all these vessels. It's going away. And as blood rushes away, of course, pressure is going to fall. Remember, there is a relationship between having more blood volume and pressure. So as the blood volume in the aorta drifts away, the pressure drifts down. And this aortic pressure is rising. And at that spot-- it's hard to see, again. I'm going to just circle it to draw your attention to it. But at that spot, you'll see the aortic pressure is slightly below left ventricular pressure. And because the pressure is slightly below, all of the sudden, this is no longer blocked. Now you've got a free path here. This valve opens up, and blood can come in. So new blood can come in from the left ventricle. So blood starts rushing in. And of course, the left ventricle is still contracting, so it still continues to rise. And it gets to about there. And the aortic pressure is going to rise. And so let me draw that. Actually, I might have switched colors, but you'll forgive me. It starts to rise. And it follows the course of the left ventricle. So basically, it's rising with the left ventricular pressure because there's a continuous space there. There's no valve between the two. So what happened at this spot exactly? Let's just recap it. Well, the AV valve is still closed. Nothing has changed there. But the semilunar valve opened. And that's the interesting new thing. That's the cool, new thing that allowed the blood to go from the left ventricle out into the aorta. And now what happens? Well at some point, all this contraction I've drawn relaxes. It finally goes away. It goes away on both sides. And all these black arrows, I'm going to erase. And this muscle now, instead of depolarizing, begins to re-polarize. Now, why didn't I erase that last black arrow? Because again, there is some pressure in the left ventricle. And in fact, looking at my graph, you can see there's not just some, but there's a lot of pressure still in there. So all that's changed is that the muscle is now relaxing. And if the muscle is relaxing, then this yellow line begins to drift down. And if the left ventricular pressure drifts down, so does the aortic pressure. That drifts down too. Well at some point, what will happen? Well, the aortic pressure is still high. And think about this. This is actually a tricky point. It's still high because there's resistance. Remember, there's resistance from all of the blood vessels. There's resistance here. All these blood vessels are offering lots of resistance. So, with all this resistance from the blood vessels, the aortic pressure stays high. And the left ventricular pressure is relaxing. It's drifting back down. And so this arrow, instead of blood just going one way, there's a little bit of pressure coming back the other way. There's a little bit of pressure going this way, this way, and this way. And there is some pressure this way still because the left ventricle still has some pressure. So they're matched. There's pressure coming from the aorta and also pressure coming from the left ventricle. Initially, the left ventricle just overwhelmed the amount of pressure in the aorta. But as it's drifting back down, now that aortic pressure is matching the left ventricular pressure. And at this particular moment, that left ventricular pressure is going to be lower than the aortic pressure, something like that-- an interesting cross-over. And that's, again, because the aortic pressure stays high because of all that resistance, but the left ventricular pressure continues to drift down because it's relaxing. And the moment that the pressure in the aorta is greater than the pressure in the left ventricle, this shuts down again. So that valve slams shut. And so at that point, what would we say? Well we say, well, the semilunar valve closed, and the AV valve opened. Sorry, I keep saying that, and I apologize. The AV valve is still closed. I didn't mention anything with the AV valve. That's still closed, as it has been for the last two points on our graph. In fact, let me just label this point one, point two, point three. So at this point, what's the next thing that's going to happen? Well, the left ventricle continues to relax, and it goes all the way down through my word, semilunar closed, all the way down almost to 0. And before it gets there, before it gets all the way to 0, the pressure's so darn low in here that now, left atrial pressure is actually higher than left ventricular pressure. And blood can flow back through. So if blood can flow back through, then we know that as blood fills up a ventricle, the pressure continues to slowly rise over time. And it gets to about there, which is the same spot that we began at. And meanwhile, the aorta continues to drift down because, just as in the beginning, we said well, when time passes, blood drifts down through to all the vessels. So blood is now drifting away, as it did before, into all the vessels. And as it drifts away, the pressure in the aorta drifts back down again. And it goes something like that. Actually I guess further, because my second is not there-- something like that. And you have to assume, based on my drawing, that these two points are the same. And if they're not, then I haven't drawn it correctly. So that's what the aorta does at the end. So let me just label this now, this last point here, this point four. Sorry, before I get to point four, point three, the thing that was interesting and new-- I should just box it. I'm just trying to box the things I want to draw your attention to-- is that the semilunar valve closed. So what is happening at point four? Now at point four-- a couple things. The AV valve now finally opens. I said that prematurely before. And that's the new thing. The AV valve opened. And the semilunar valve is still closed. So that did not change. So this is exactly what happens at the four stages, the four important points. So, just to recap-- and actually, as I recap, let me mention something new that's interesting as well. Remember that when valves close, they usually make noise. So it's like a slamming of the door. So when a valve shuts, it makes noise. And so you have to look on these four points, when does a valve close for the first time? Well, the AV valve closes right here. This is the point where it first closed. So when the AV valve closes, it makes a loud thwack, a loud noise. In fact, sometimes people call it a lub. You hear that lub noise if you listen to your heart. And that's the first heart sound because that door just shut. And you can see, based on the pressure differences, it's really closing because the left ventricular pressure is going up so fast. So when you hear that first lub-dub, when you hear that lub, that's also the beginning of the high pressure, the contraction of the left ventricle. Now point two, does any door close? Does any valve shut? Not really. The semilunar valve opens, but opening of a valve doesn't really cause any noise. At point three, the semilunar valve closes. So that's where the aortic valve and pulmonary valve slam shut. So again, you get some noise up here. This causes noise. So at point three, if I was to draw a straight line down here, you'd get some noise. I'm going to cover up my number four, but that's OK. You know where it is. And this is the second noise. And it's coming from the closing of the semilunar valve. And then, point four, the AV valve opening, well, opening doesn't create noise, and the semilunar valve is still shut. So really, the two sounds, the heart sounds, S1, S2, come from the closing of the AV valves initially, the mitral and tricuspid. And then the dub comes from the closing of the aortic and pulmonary valves.