Health and medicine
- Pressure in the left heart - part 1
- Pressure in the left heart - part 2
- Pressure in the left heart - part 3
- Left ventricular pressure vs. time
- Left ventricular volume vs. time
- Drawing a pressure-volume loop
- Understanding the pressure-volume loop
- End diastolic pressure-volume relationship (EDPVR)
- End systolic pressure-volume relationship (ESPVR)
- Reimagine the pressure volume relationship
- What is preload?
- Why doesn't the heart rip?
Ever wonder exactly how the left ventricle's pressure changes over time? Find out in this color-coded video! Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
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- How much do the relative proportions of contraction and relaxation discussed in the video change with rising heart rate?(5 votes)
- As HR increases, the time available for Ca sequestering (Ca removal from cell=cell reset) starts to decrease. This means that more Ca is in the cell than normal. This also means that Ca is more likely to be released from intracellular stores via Ca-induced-Ca-releasing pathway. This also means that Ca is more likely to bind to Trop-C on the myosin. This translates into the reduction of wait time in the Cardiac cycle, which is contract-reset-wait for Ca availability-contract-reset..... As we can see this is an over simplification but it works to illustrate the key-point. As we increase our HR we increase the intracellular Ca concentration because we do not have time to remove it, which reduces the wait time needed to initiate contraction of the heart because the necessary Ca needed to start the different events for contraction is already at hand; thus HR increases. This will happen until Ca-wait-time is reduced to a maximum extent (thus HR is max) and can only be maintained for a short time. This is because Ca is toxic to cells and if Ca remains in a cell for too long a time at a certain level it will initiate cell death cascades. If we push bodies past the max ability of the heart to pump, the different tissues of the body begin to break down as they begin to starve. This then leads to a systemic cascade of badness that ultimately leads to death.
So, as contraction speed and force increases, the relaxation time decreases until each is at their max increase and max decrease. Thus, the ratio will shorten somewhat, but it is predictable and fairly constant. (I wasn't sure exactly what you meant so I tried to answer in a way that could lead to clarification if it does not provide it.)
Note: The initiating event for an increase in HR can be controlled voluntarily (choosing to run), or involuntarily (being scared-ANS activation, drugs, poison).(5 votes)
- can you explain me about right ventricle of heart and about heart beat?(3 votes)
- The right ventricle contracts at the same time as the left ventricle. It contracts first at the apex and the signal is conducted superiorly towards the valves. Contraction causes pressure to rise and the tricuspid valve to close causing (along with mitral valve at the same time) the S1 heart sound or 'lub'. Then after isovolumetric contraction the pulmonary valve opens allowing blood flow into the pulmonary artery. The right ventricle relaxes and the pulmonary valve closes leading to the S2 heart sound or 'dub' (again with aortic valve). The pulmonary artery also has some compliance leading to a dicrotic notch in the pressure/time curve as occurred in the aorta. The right ventricle continues relaxing (isovolumetric) and the tricuspid opens again draining the right atrium. Overall, the pressure/time curve looks much the same as the left ventricle but the pressures are lower. This makes sense as this side of the heart only needs to work hard enough to pump blood through the lungs and not around the whole body. http://img.tfd.com/ggse/da/gsed_0001_0023_0_img6734.png
This is a great question because there are some key differences between the right and left sides of the heart and we usually talk more about the left side. First, the left atrium contracts slightly after the right atrium. This difference is called the interatrial conduction time but is fairly insignificant compared to the atrioventricular conduction time (10msec vs 100-200msec). Second, the S2 heart sound can separate into two sounds during breathing making the heart beat sound 'lub dudub', called physiological splitting. This is because during inspiration there is a decrease in pressure within the chest (as the diaphragm pulls down); this translates into the pulmonary vessels. This means the pulmonary valve (in the right ventricle) will close later than the aortic valve (in the left ventricle) causing the 'dub' of 'dudub'. During expiration the two sounds come back together and the sound returns to a 'lub dub'.(6 votes)
- Can you explain me why did you put the (atrial) systole in the curve left (ventricular) curve, please?(3 votes)
- i think he said in the previous video that the pressure during atrial systole will be increasing in both of the left atrium and the left ventricle , since the mitral valve at that point is open
and the two spaces are continuous
so that rise in pressure you are asking about does exist in the left ventricular pressure curve too cuz this "pressure increase" occurs in the ventricle too not just the atrial systole(4 votes)
- 2:50to3:20Is the temperature of the blood going up during this time with the two valves closed, pressure going up but volume staying the same?(3 votes)
- Realistically yes, but it is not sig. The time it takes to raise temp of blood is not available initially and does not play a sig role, temp is hemostatically controlled. However, (again) as HR increases so will temp of the blood over time. This becomes sig in the breakdown of proteins and protein function more so than with increasing pressure because blood vessels are very complaint. It is the contraction of muscle which creates heat and the transfer of heat from muscle to blood over time and its effect on the proteins that is sig, not the effect temp has on blood pressure, because the body adapt to and function at different levels of pressure very well, but it cannot function well outside a small temperature range.(4 votes)
- I am confused by the pressure in the graph, is it the force exerted by the ventricles or the pressure by the blood on the ventricles? Its not making sense to me either way, can you please explain to me what pressure it is in the graph(3 votes)
- The pressure in the graph is the recorded pressure generated by the left ventricle through one heart beat or ventricular contraction. The left ventricle is the chamber that pumps the blood out to the systemic circuit, or the body during ventricular systole. In order to push the stroke volume or a portion of the blood out of the ventricle, the left ventricle must contract, causing pressure to increase as the ventricle's size gets smaller. Typically, it will generate something around 120 mmHg of pressure to overcome the systemic vascular resistance so it can push the blood into the aorta and to the body. This is the systolic pressure. The diastolic pressure in the left ventricle is very low, as the heart is relaxing and filling with blood. As the blood fills that volume of space, a small increase in pressure is noted on the graph in the video. (Any closed container that has a volume of fluid added to it would record an increase in pressure.) These pressures are obtained from special catheters that must be threaded into the left ventricle using peripheral blood vessels. If we check the pressure recorded by a blood pressure cuff on the brachial artery when the heart is filling with blood it is much higher, about 80 mmHg. That pressure is actually due to the elastic recoil in the arteries that pushes the blood along, making the pulse. So blood pressure taken with a blood pressure cuff on the arm is 120/80 mmHg. He is also inclucing what valves are open and closed. Take a look at the wikipedia page for an overview. Also, I like this site at a Utah school that has tutorials too. I hope this helps, the heart is complex and takes time to figure out. https://en.wikipedia.org/wiki/Cardiac_cycle
- in the part of isovolumetric relaxation u said that the blood has no where to go ...
now where does that blood come from if the ventricle has just finished contracting and pushing blood into the aorta ?
or there is some blood that remains in the ventricle even after contarction is over and aortic valve shuts ?(3 votes)
- 50% to 75% (as I recall) of blood leaves the ventricles. Thus some is left over after contraction. Isovolumetric is the stage where pressure builds until it can over come the pressures above it or below it, thus all valves are closed in the heart as pressure builds but no blood flows. This can be good (valve opens in proper direction due to pressure) or bad (valve opens in the wrong direction due to pressure), depending on which way the blood is suppose to move. if the pressure is over come in the wrong direction (seen in faulty heart valves) you get ventral or atrial regurgitate of the blood (blood moving backwards).(3 votes)
- During the second half part of the yellow line (at the top), there is relaxation of the ventricles therefore the left ventricle pressure drops, then why it is considered under the systole at the end of the video ?(4 votes)
- At6:44"So same volume. Isovolumetric relaxation, and that's this part right here. Because again, the blood has nowhere to go, and the left ventricle is relaxing."
I would like to ask, since the Pressure is going down, shouldn't the Volume go up? Ty :)(3 votes)
So the main thing I wanted to do in this video is just show you the timing of a heartbeat. And we've been drawing the left ventricular pressure. And so far, I've just sketched it out. But now, I want to try to be a little bit more careful with how I draw it so that you can get a real appreciation for how long everything seems to take. So these numbers I'm going to write up are just estimates. They're not exact numbers. And of course, you know that many things change how fast or slow a heartbeat can be. But they give you a real sense for the timing. So let's get started. The left ventricle-- it begins, we know, with a pretty low pressure. Let say this is about 50 millimeters mercury. I'm just going to estimate this is about 10. And we know that it's going to begin contracting. And I have to pick a point somewhere, so I'm just going to pick this point right here. It begins contracting at a pretty low pressure, about 10 millimeters of mercury, let's say. And right before it contracts, the last thing that happens, remember, is atrial systole. And it's a lump in the pressure. The pressure goes up, and then it slightly goes down. And that's because of the atria contracting. And before that-- I'm going backwards now, you see that? Before that, the atria and the ventricle are just slowly filling up with blood. And so the pressure's just slowly creeping up. So that's the first step in terms of what the left ventricle pressure looks like. It creeps up and then has that little bump in the end. Now, it has to go from that point to a very high point. When the ventricle contracts, it's going to skyrocket in pressure. And let's say it's going to get up to around 80 or so. And it doesn't take much time. It actually does it all in about 0.05 seconds. It just shoots up like that. So it just skyrockets up. So that's the next step. It rockets up. And really, let's talk about these two points real quickly. These points here-- let's call this B and I'll call this A. And so between A and B, what's happening exactly? Well, the big event at A is that the mitral valve closed. So I'm going to write mitral closed. And then, of course, at B, the big event is that the aortic valve opened. So I'm going to write aortic opened. And you know when I write aortic, I mean the valve, not the artery, because of course, the aorta is just an artery. It's always open. But the aortic valve opened at that point. Now, between those two-- and this is actually really a cool thing to think about-- between those two, what's going on? Well here, when the mitral valve closes to the point where the other one opens, you've got a chamber, the left ventricle, with kind of a room with two doors that are closed. There's nothing open between these two spots where I've drawn the red. And so because all of it's closed, we actually have a special name for this because there's contraction going on. The left ventricle is contracting. So we call that contraction. But because there's a room with two doors closed, the blood has nowhere to go. So the volume of blood is not going to change. It's going to be the same. And the medical word for that is "iso." "Iso" means same. So isovolumetric, same volume. So contraction. And all that means is that hey, the left ventricle's contracting. And oh, by the way, the blood volume is not changing, because there's nowhere for the blood to go. So a fancy word, but that's what it means. So now the blood is going to start entering the aorta up here. And it's going to really get a high pressure. And we know that it's going to take a little bit of time for all that blood to go into the aorta. In fact, it takes about a quarter of a second. And at the end of it, we know that the pressure is going to be somewhere around 100. It's going to be around 100, but my blood pressure is going to peak out somewhere higher than that, somewhere around 120. In fact, I know that, because whenever I go to the doctor's, they always check my blood pressure. And they tell me, hey, Rishi, your blood pressure's around 120/80. So this is helping me draw my graph. So I can say, well, I know it has to get up to about 120, because that's what my doctor told me it was. And at some point, it's going to dip down again to this point. And I'm drawing it at 100, because we know that the aortic valve is going to close at some point. And then, of course, you remember that whole dicrotic notch bit. But that's roughly what it might look like. In fact, let me actually just draw that with a yellow. And the yellow just reminds us that now, at this point, blood is entering the aorta. This whole yellow bit is blood going into the aorta. And of course, you get to another important spot here. And you remember, let's call this spot C. Here, the aortic valve closes. So this is where the valve now says, hey, enough is enough. Let's shut down, because pressure is going the other way. And then, our blood pressure is going to fall. It's going to fall, and it's going to fall over a bit of time. It's actually going to take about 0.15 seconds. And it's going to go to about, let's say-- I'm just sketching it out-- let's say about here. So about that point, let's say, and it's going to fall, fall, fall, fall, fall. And why did I choose this point? Well, that's the point where we say, well, this is where what happens? What happens at this point? The mitral valve opens. The mitral valve opens at that spot. And then, of course, the pressure continues to fall. It gets pretty low, and then eventually it has to get back up to where we started. Otherwise, the next heartbeat is not ready to go. So we have to creep our way back up as the blood fills in, and we're done. So this part right here, this third segment, where I'm going to use green, again you have the aortic valve is closed, but the mitral has not yet opened. And so does blood have anywhere to go? Nope. Again, it's stuck in a room. So if the blood is stuck in the left ventricle and the left ventricle is relaxing, then you better believe we're going to have a fancy word for it. We're going to call that relaxation. I guess not that fancy, but the first part of it is "iso," same, volumetric. So same volume. Isovolumetric relaxation, and that's this part right here. Because again, the blood has nowhere to go, and the left ventricle is relaxing. And the last chunk out here, I'm going to do in a different color-- blue, let's say-- is where blood is slowly just filling back into the left atrium. And obviously, since the mitral valve is open, also the left ventricle. So these are the four segments. And you might think well, wait a second. What about that first segment? I didn't color that part in. And what I'm going to do instead is I'm going to say, well, let's say this is 0.2. So I'm going to do the same thing over here. I'm going to say what about the point 1.2? That would be equivalent. I'm going to say blood pressure keeps rising. And let's say we have our little atrial systole, something like that. So just to make it continuous instead of drawing two separate chunks, I think this will prove to you that it's basically the same thing. So this is getting ready for the next heartbeat. But in terms of time, you would agree that that's the same segment. So, then if I was actually to chunk it out, this part right here-- I'm just going to draw it on the timeline axis-- is about 0.5 seconds. I'm going to try to draw it big. I said 0.5, sorry. 0.05 seconds. My mistake, sorry. So 0.05 seconds. The next chunk, this bit right here, is about 0.25 seconds. So you could say about a quarter of a second is right there. This is about a quarter of a second. And then you've got the next chunk. This is about 0.15 seconds. And again, these numbers are not super important, but I just want you get a rough sense of simply the fact that this is actually not the same as the contraction bit. So it's a little bit longer to relax. So just get that intuitive feel for that. And then finally, this last bit. This is obviously the longest bit. This is just going on and on and on. This is going to be about-- holy cow, it's long-- 0.55 seconds. And of course, if you add up these four numbers, if you add them all up, they should add up to 1 second. Because the whole point is that this is all happening in about a second. And that's if we assume, of course, that our heart rate is 60 beats a minute. Now, that is not always true, of course. Certainly sometimes it's much faster than that. But if we assume that, just for the sake of getting a sense or a feel for this stuff, then this might be a rough estimate of how it might look. Now, one thing that I've always thought is kind of interesting. When you look at this stuff, you think, OK, well, which parts are systole and which parts are diastole? And these two, if you chunk them together, if you add them up, this makes up your systole. So that's a nice way of thinking about it. And if you then add up the rest of it, this whole bit right here, this is your diastole. And you remember, we have talked about how the fact that diastole is about 2/3 of the time and systole is about 1/3 of the time. And you can see how that's basically true here. And now, the final thing-- this is actually something that always threw me off, confused me a little bit-- is this chunk right here. I've always wondered why this isn't part of systole. It certainly looks like it's part of the lump, or the big mountain drawing. But the truth is that we have to remember that the left ventricle is relaxing during this time. And diastole is all about relaxation for the left ventricle. So because it's part of relaxation, it is technically and truthfully part of diastole, even though it looks like it's part of the lump. So just keep that in mind.