[BLANK_AUDIO] Okay, so we've been through the ECG tracing at the top of this illustration. Notice that the illustration's also showing us heart sounds, pressures, ventricular volume and then some of the valve action that occurs in the heart. Let's focus on the pressures, for a minute. Because you now know that it's pressure changes that are going to cause valves to open and close, and prevent a back flow of blood, right? So, if we go up to the P wave in the ECG trace and just follow a line down the page, you'll be able to see that the P wave is following very closely by changes in pressure in the atria. Yeah, you see it? >> Mh-hm. >> So you see that little bump in atrial pressure, which we're calling atrial systole. Have you heard that world before, systole? Mia? >> We hear it when you talk about blood pressure. Like systolic blood, blood pressure. >> Aah. And what, what do you think systole refers to? >> Maybe contractions? >> Yes. So anytime you see systole, like systolic blood pressure, it's the pressure that's created by ventricles contracting. Here we're looking at atrial systeli and so what we're thinking about is that period when the atria are contracting, okay? And so you see that atrial systeli creates a little bump in atrial pressure. Why do you think it's just a small bump? Remember anything about the thickness of the atrial walls? Natalie. >> Well they're thinner, and they can't push as much out as the ventricles can? >> Right, so they're thinner, which means when the atrial walls contract, they don't generate as much force as we'll see the ventricular walls are going to generate, right? Cool. Okay, so we see atrial sistole happening and then notice that the atria kind of relax. And pressure stays kind of low in the atria after that. Right? Going back up to the ECG tracing. Look at the QRS complex and then follow it straight down the page and you'll see that the QRS complex begins. And it's followed almost immediately by an increase in ventricular pressure. So exciting the ventricular cells, which is what happens during the QRS complex, right? That excitation caused the ventricles to contract. And so what's ventricular contraction going to be called? What's that phase called? >> Ventricular systeli? >> Exactly. Ventricular systeli. So the QRS complex, triggers ventricular systole. And what we see, if we look at that left, that left ventricular pressure line, what we see is that ventricular pressure begins to increase. Now at some point, very quickly, ventricular pressure increases and it crosses over that pink line. What happens at the point where ventricular pressure increases above atrial pressure. Sure. Yeah. >> Would that be when there's the closing of the AV valves. >> Exactly, exactly, and that's when the AV valves close, that's what makes them close. And in this picture, we're looking specifically at the pressure in the left ventricle, and the left atrium. And so at that point where left ventricular pressure gets higher than left atrial pressure specifically what valve closes? [INAUDIBLE] >> The mitral valve. >> The mitral valve closes, right. But then, pressure continues to rise in the left ventricle because the ventricle is still contracting, right? And if you follow that pressure line upward, you'll see that eventually pressure in the left ventricle becomes higher than pressure in the green line, which is representing pressure in the aorta. Now, at the point where left ventricular pressure is higher than the aortic pressure, what's going to happen? Andre? >> The aortic semilunar valve opens? >> Exactly. And so that would be the point at which the ventricles really begin to eject blood, right? Okay, exactly right. So the aortic semilunar valve opened at the point where the left ventricular pressure got higher than aortic pressure. So blood is getting ejected out of the heart. Blood is going into the, aorta because we're looking at the left ventricle. So blood is being ejected into the aorta. Notice that the pressure continues to climb in both the left ventricle and in the aorta. Left ventricular pressure is continuing to climb because the left ventricle is continuing to contract, right? Even though the valve is opening, the ventricle is still contracting and pushing on the blood that's present there. Pressure in the aorta is increasing during this phase, because the left ventricle is pushing blood out into the aorta. So, you know as more blood gets injected into the aorta, the blood pressure will increase. Okay, but you know what happens in the heart is we have contract, contract, relax, right, and so after reaching a peak, you can see that the left ventricular pressure begins to fall. Now at some point, left ventricular pressure falls below the pressure in the aorta, that green line pressure. What happens at that point? Natalie. >> Then the semilunar valve, or the aortic valve would close. >> The aortic valve closes, and what would be the benefit of the aortic valve closing? >> It will prevent the back flow of the blood back into the heart. >> Exactly. It prevents blood from flowing backward from the aorta into the left ventricle. So, the left ventricle pressure falls below aortic pressure. The Aortic valve closes but notice at the left ventricular pressure continues to fall. And that's because the left ventricle is continuing to relax, right? At some point, the left ventricular pressure falls below the left atrial pressure and what happens at that point? [BLANK_AUDIO]. >> Is that when the AV valves open back up? >> Exactly. That's exactly when the AV valves open. And so the ventricles will be able to start filling with blood. So that they're ready to pump again during the next heartbeat. Excellent. Great. Now if we wanted to continue on down the page, one of the things that we really do need to think about, is ventricular volume because the whole point of the heart beating, is because we want to eject blood into the systemic or the pulmonic circulations, right? And so, if you'll notice in this illustration what you can see is that they're showing you ventricular volume. And you can see that ventricular volume is fairly high at the beginning of the graph. And you know from looking at the pressure curves that are represented up above the ventricular volume, you know that at the beginning of the graph we're in a period of a trio relaxation, ventricular relaxation, right? So pressures are low everywhere. That's a period of time when the ventricles are filling with blood, and so ventricular volume is pretty high. Notice atrial systole, if you look at what happens to ventricular volume during atrial systole what do you see Andrea? >> Oh, it still continues to increase. >> Yeah. Yeah. But it doesn't increase them a, a whole lot. Right? But there's a slight increase in ventricular volume. So, when the atria contract, they do push just a little bit more blood into the ventricles. Right? Then the atria relax and we're getting ready for ventricular systole. When the ventricles actually contract, you see ventricular pressure going up, right? Notice what's happening to ventricular volume. [BLANK_AUDIO]. >> Then it decreases? >> Yes! It decreases, so during ventricular sistole, while the ventricles are injecting blood, ventricular volume falls. Exactly what you would think, right? Now we finally get to the lowest volume in the ventricles, you see it? The place where the ventricular volume is the lowest. And then you see that ventricular volume starts to increase again. Now, some valve changed its state to allow ventricular volume to begin increasing again, which valve was it? >> The AV valves. >> Exactly. When the AV valves open, blood begins to passably flow from the atria into the ventricles once again. Right? So, I know that we talked about systole, and said that that's the contraction event of the heart. What's the relaxation phase called? Mia? >> Diastole? >> Diastole, yes. So, the ventricles fill with blood during what period? >> When it's relaxed. >> Yes, so that-. >> The ventricles will fill with blood. So during diastole? >> Ventricular diastole. >> Ventricular. >> Yes. Yes, the ventricles fill during ventricular diastole and they eject blood during ventricular systole. We're just practicing using the term so that you feel comfortable saying them. And your friends will think you're highly educated. [LAUGH]. >> All right. So, now there are a couple more pieces that we've talked about far as we've learned about the heart and its function that are also represented in this illustration. Notice up at the top of the illustration. The heart sound tracing. Heart sound one is caused by what event in the heart? Yes Steph. >> When the AV valves close? >> When the AV valves close. And so we could say that heart sound one indicates the beginning of what phase in the heart? >> Ventricular sistole? >> Ventricular sistole, yes. Exactly, and then hearts on two, I see that a little bit further along. What causes heart sound two? Mia? >> When the semilunar valves close. >> Exactly. And so s two, heart sound two actually represents for us or tells us what? Phases starting. >> Ventricular systole or diastole. >> Exactly, ventricular diastole is starting. Right. Good job. I think we've pretty much covered all of the cardiac cycle. But you will all have to do, is review it a couple of times. Just so heart function really starts to make sense. [BLANK_AUDIO]
