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Current time:0:00Total duration:12:44

Video transcript

so we've talked about the pressure in the left ventricle and the aorta and I thought it would be kind of fun to kind of sketch it out again but I wanted to go into some details because when we did it last time I brought up some issues but kind of quickly glossed over them and you may be wondering about them now so I thought we would kind of get into some of the details and finer points of the pressure and the heart the left side of the heart so you know we usually think pressure in millimeters of mercury so that's why I want to just kind of write that out so it's clear and I'm going to sketch out the pressure tracing we said happens with the aorta and the left ventricle so first a lot ventricle we said that the pressure rises kind of slowly and then eventually the left ventricle is going to contract really hard and that's the real cause of why the pressure rises abruptly and then it relaxes and eventually as it relaxes more it kind of Falls and then blood kind of riku malade sin to that or falls into that chamber from the left atrium and that's why the pressure kind of goes back up again so that's kind of a very quick way of thinking about the left ventricle and then of course you have the aorta and I'm actually going to do the a or a little bit more slowly they ordered of course there's blood leaving the order going to different parts of the body and then let's let's stop it right there and now kind of talk about exactly what happens when the pressure of the aorta and the left ventricle cross so let me draw for you I'm going to draw on the side kind of what this looks like in the body so you've got the left atrium here and then you've got the left ventricle kind of coming off and is enormous right so just draw it that way and then there's the aorta also kind of a large vessel coming off of the left ventricle and the aorta kind of wraps around and goes down but it leaves a few branches right it has a few branches one there one there and let's draw a third one so classically kind of three branches coming off of the arch called out the arch of the aorta and then that's the aorta kind of there so let me label this stuff this is my aorta this is my left atrium and my left ventricle so what is happening I'm going to draw a little blue arrow than to start us off what is happening right there well at that point we know that we have a couple valves this is let's say our mitral valve here mitral valve and I'll label up mitral and while I'm at it I'll draw in the aortic valve here and this is my aortic valve so these are my two valves the mitral valve is closed and remember it closed actually a long time ago well I shouldn't say a long time because not a lot of time is passed between these two points but it closed over there so if I'm going to show it closing I'm going to have to kind of I'm just going to block it off just to make it very clear that it's closed really no blood can pass through that gate right so we're in the middle of contraction and and I'm going to draw pressure with yellow arrows so you've got a lot of pressure kind of coming in here because of the contraction of the left ventricle a lot of lot of contraction there a lot of pressure and the question is is the aortic valve open well if I'm talking about my blue arrow on my figure well not really right it still hasn't gotten the same pressure that the aorta has so the valve is still closed so really both valves are closed and pressure is building in the left ventricle now as the left ventricle pressure increases even more as it increases even more and rises let's say we get to kind of this point well all of a sudden now the pressure is greater than the aorta so let's actually show that by drawing a little opening there so now that Valve opens right and you actually have blood flowing this way flowing this way and actually of course it flows into all of these different places right so it starts flowing through the aorta through all the vessels but one thing that often is forgotten is that the aorta is actually compliant compliant let's actually write that out because that's that's kind of the big key for understanding how the aortic pressure tracing looks so compliance all right compliance and what is compliance mean it basically I kind of think of it as stretchability stretchability so if you can actually stretch these vessels and you can then you can begin thinking about them almost like you would think about a balloon right they're actually stretchable the vessels themselves and so while there's blood kind of rushing around it's also kind of pushing off into the walls right the walls themselves are going to kind of stretch because I said it's a little bit like a balloon and really what you get is you actually get these walls are no longer going to be as they look now they're going to stretch out and so you get something like this you basically get stretched out vessel something like that right so this is actually quite interesting because now it begins to look balloon like and what's actually stretching it out well blood is stretching out right it's not like you're using a puff of air or something like you would for balloon literally blood is pushing into the walls and stretching them out so you've got blood in here that's what's causing the stretching so while you have stretching the vols you actually have increase of aortic pressure so the aortic pressure starts to rise and that's what the tracing looks like right so rises to that point so that's the most pressure that's in the aorta at any given time right so this is the point when the walls are actually maximally stretched so this is where there's maximal stretching of the walls right here and then you can see the left ventricle pressure starts falling and as it falls so does they or tack pressure because it's all a continuous space right but as this is falling as it starts to fall what's happening this is my question what's happening to the walls well at that moment when it begins to kind of fall again the walls remember they're like rubber bands the moment that you put less pressure on them they're going to start to recoil then immediately they start to recoil so they start doing this right they're recoiling and so you've got two things happening as these yellow arrows in the aorta are being created and then those yellow arrows represent kind of recoil the yellow arrows in the ventricle are disappearing remember that's contraction so you have this passive process we think what is kind of a passive process here passive passive recoil remember that is kind of this elastic energy elastic energy and I say passive because it's elastic and it's not chemical energy and in the ventricle you've got this active active contraction I just want to kind of contrast the two right active contraction is using chemical energy right when the ventricle contracted we were basically burning up a bunch of ATP right that's how we got that so remember that's ATP when I say chemical I'm talking about ATP whereas when I say passive recoil its passive because it's not using chemical energy but it is using elastic energy and that was actually stored up remember that was stored up energy and when was it stored up but will stored up when the left ventricle first forced blood into the aorta so you stored up some energy and now those rubber bands are recoiling and so it's a very natural process makes sense and so while we're on the down hill of our pressure slope the bands are recoiling and now eventually what's happening is that pressure here is rising just slightly from the fact that you've got some recoil and pressure here is falling quickly because basically now this process of contraction has gone away right on the downswing of the left ventricular pressure these arrows go away so at this point now you've got slight increase in pressure in the aorta slight decrease in pressure in the left ventricle so what's going to happen well at some point the pressure in the aorta is actually going to slightly exceed exceed the pressure in the left ventricle so again this point the point where you actually have more pressure in they order than the left ventricle you might be like well how could that ever be there aren't they continuous right they are continuous but a different process is happening here then here here you've got less pressure in the left and go less pressure because the contraction is stopped and the aorta you've got more pressure because you've got recoil of the walls so as the pressure gradient switches now you've got more pressure in the aorta what happens well you've got a little bit of blood of pushes out this way and pushes out this way because of course the walls are coming back in and the moment that there's slightly more pressure on the aortic side this valve snaps shut hey or dick valve snaps shut so now that valve snaps shut and that's very interesting and that's actually a very critical moment because let me actually make some space here and this is all happening of course within fractions of a second right that valve snaps shut and there's blood that literally kind of wanted to go in and end up basically gets the door slammed in its face and it actually kind of recoils and goes back around so it wanted to kind of go towards the left ventricle the aortic valve snap shut and push that blood back into the aortic space and of course if there's always blood kind of snaps back what's it going to do it's going to push again it's going to push back just like it did the first time out on those walls so these pressure arrows reverse these pressure arrows reverse and you actually get pressure going the other way because of this snapback so you might think well you know that's such a small amount of blood how can it make such a big difference but it does that tiny amount of blood that hits off of the aortic valve pushes back into the aorta and actually increases the pressure in the aorta so let me actually write that out very formally here you actually have a snapback snapback that's just my own terminology of blood bouncing off the aortic valve bouncing off a or t'k valve okay so now it's really clear where that pressure is coming from it's coming from the snapback of blood and as a result you actually have a slight pickup of pressure in the aorta so now blood is going to kind of re-enter the walls here right re-enter the walls and now finally you've got your aortic valve closed and you've got blood in the walls and blood kind of leaving as it always has through all these different routes right leaving through all the vessels going to the different parts of the body so at the end of this what's going to happen well eventually all this blood is going to kind of want to leave it's going to all kind of want to leave and the walls will basically kind of empty out so all this blood will kind of finally leave empty out and the walls kind of go back to the original shapes let me just show them in their original shape and the whole process can start over again so these walls go back to where they were when I first drew them something like that and this is of course due to the fact that the the rubber bands are basically back in their natural position and as that's happening blood is kind of draining off to the different parts of the body and you basically get something like that so this point and this point are the same so you really kind of come full circle right and what you get here what it looks like is a knotch right because pressure goes up here and it comes down here so it basically looks like a little notch now before I drew it kind of just more straight I didn't really draw that notch because it was a little bit clearer to show that the simpler way but but truly this is actually what happens in this knotch is called a dicrotic notch dicrotic notch so I'm going to draw this again for you with the dicrotic notch and you'll see how it differs from the way we drew it before the way we drew it before this is the inaccurate way was something like this I said well it goes down like that well accurate the more accurate way would be to say okay goes down but then there is actually a notch that kind of comes in there so this increase this difference is because of the compliance of the aorta