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Current time:0:00Total duration:13:02

Video transcript

so we've talked a lot about pressure and time and how pressure actually changes in the left ventricle over time and I'm going to kind of take that one step further by describing to you what happens in the left atrium over one second so still kind of the same way we've been looking at it with pressure and time on the two axes and of course pressure goes up in that direction let's say this is about 100 and let's say zero is down there and I'm going to measure it all in the same units millimeters of mercury so let's start with the left ventricle and we know that the left ventricular pressure kind of Rises steadily and then it contracts really hard right so it kind of has this huge contraction which increases the pressure dramatically and then it kind of bottoms out as the left ventricle relaxes and then it kind of slowly picks up again and pressure as more blood fills in and of course then you have your aortic pressure as well I'll put the aortic pressure in yellow and they or tech pressure is actually kind of slowly drifting down and then it kind of picks up along with the left ventricle goes for a nice ride and then at some point the aortic pressure actually kind of exceeds goes higher than the left ventricle pressure that's because of the compliance of the aortic walls and you get this kind of knotch this what we call a dicrotic notch and then you just make sure I kind of end it in the right spot something like that so that's kind of what the aorta is doing and this is our aorta pressure curve a or tack curve and this of course is our knot CH not CH and the name of our notch is dicrotic notch dicrotic notch so you'll see that word now what's happening with the left atrium well the left atrial pressure is basically the same as our left ventricular pressure for a little while and I'm actually going to sketch it out on the side so you can kind of get a visual idea of what's happening in the left ventricle and the left atrium during this time so you know you've got the aorta coming off and let's draw big ventricle down here and our atrium our left atrium which is right here is getting blood from two sources right the left and right pulmonary veins so this is our left pulmonary vein and of course then there's the right pulmonary vein and let me actually finish off the aorta first before I draw the pulmonary veins so this is our pulmonary vein kind of going from behind and this is coming from the other lung right so this is our right pulmonary vein so these are our two sources of blood this is where the blood is really coming from and the pulmonary veins have blood that's coming with a little bit of pressure right a little bit of pressure with these veins and so blood is kind of coming in this way and it's staying in the you know at times in that left atrium and why is it staying there well because there's a valve here right there's no valve that separates the left atrium from the pulmonary veins there's no valve there but there is a valve here there's also a valve in here so these valves we know this is called the mitral valve mitral valve and that separates it from the ventricle and on the other side you've got your aortic valve the aortic valve and at the beginning kind of the beginning of this process what's going on well you've got the there's a free kind of space here and he had make it very clear there's space here between the left atrium and left ventricle the valves are not closed right and you are actually getting blood flow this way so really the way why you think about is the left atrium left ventricle are really one giant chamber at this point right there's no difference in the two and so of course the pressure would be basically the same and so I'm trying to draw it basically the same in those two spaces right so the pressure is basically the same and the maybe a slight increase in the left atrium side and why would that be well that's where the blood is initially coming in so there's a high pressure in the pulmonary veins and so maybe there's a slight increase in pressure on the left atrium over the left ventricle but it's very similar right so this pressure tracing looks about the same but then there's a bump there's a bump here why would there be a bump well there is a process called atrial systole meaning the atrium actually contracts that's all it means so atrial systole just means that just like the ventricle likes to contract the atria can also contract and I'm going to actually put a giant red square around this letter a because we actually end up calling this the a wave the a wave so the pressure tracing for the ventricle then is not really accurate it's not really straight is it it actually has a little bump as well so because the two chambers are continuous whatever is happening in one is reflected in the other and you get this little bump there so then you get this huge so then the contraction stops right so atrial systole is over with contraction stops and that's why the bump comes back down so that's that's what explains why it kind of comes down this way now the ventricle contracts right that's the part we we definitely feel very comfortable with the ventricle is a huge contraction we know this and so of course you're going to get you know all this pressure building up and this causes this is actually going to get kind of interesting here this causes these valves this mitral valve to kind of all of a sudden close up now remember these atrioventricular valves meaning the mitral valve and the tricuspid valve those are the two atrioventricular valves they have these interesting chordae tendineae right they have these things called chordae tendineae basically little tendons or cords i guess you could use either word right chordae tendineae and what it does is it really prevents the mitral valve of course the mitral valve is going to want to close right there's no doubt about it because the pressure in here is so darn high in the ventricle so of course the mitral valves going to want to close with so that means that this arrow is gone right but these cords prevent the valve from kind of flipping backwards they don't let the valves go into the left atrium and kind of flop in the wind they really keep the valves tight now remember there's so much pressure in the left ventricle that the valves are going to want to kind of buckle in but the cord 10 they keep them firm right but what really happens interestingly is that because the contraction happens so darn quick there's blood that's actually snapping Mac just like in the dicrotic notch remember we talked about snapback of blood it really is you can think of it as crashing off of that valve so now there's actually blood crashing I'm using that word specifically crashing off the mitral valve off the mitral valve mitral valve so what would that do well if blood is crashing off the mitral valve then it's going to increase pressure in the left atrium right you're going to get a little bit of increased pressure in the left atrium so for a short time right when the aortic sorry right when the mitral valve is closing you're going to get a little bump and pressure so that explains what's happening here you gets tiny little bump in pressure and we call that this sea wave so there's a sea wave that happens so it's interesting you get this a wave and this sea wave right and then actually maybe I drew this a little bit too low and then you have over time now that the mitral valve is closed more blood coming in right so you've got more blood coming in from the two sides from the left and right pulmonary vein of course that's continuously happening except now there's no continuous space with the left ventricle so all that blood has only one chamber to sit in right not too like before only is one chamber which is the left atrium so the pressure starts rising rising rising rising rising rising in the left atrium because of course it's taking in a lot of blood and it really can't release it because that mitral valve is still shut now at some point that left atrium is going to wait it's going to wait for the left ventricle to finally have less pressure it's waiting for the pressure on the left ventricle to kind of decrease and what is that decrease well this contraction finally kind of relaxes right so all these arrows kind of go away slowly kind of go away slowly over time and you have a little bit of contraction left let's say but but really it's it's almost just a little bit compared how much there was so the pressure is almost back down and so the left atrium is filling up with blood let me show that filling up with blood so that's why the pressure is rising here and simultaneously the pressure is falling in the left ventricle so there you have an interesting difference so there you have an interesting difference because on one side pressure is rising the other pressure is falling and you're going to actually get a cross here across which means that the pressure in the left atrium left atrium pressure is actually going to be higher it's going to be higher than the left ventricle pressure so at that point of course if the pressure on one side is higher now than the other this mitral valve is going to open again so finally you're going to get opening of the mitral valve again right and blood can now in the blood can now dump in so at this point blood dumps in the left atrium is just so relieved it's like you know imagine you have to go to the bathroom and you you know finally urinate your bladder is so relieved because all that fullness is gone right the same thing the left atriums fullness is gone and so it basically kind of empties out very quickly and the pressure falls so you might be thinking well wait a second if pressure is falling in the left atrium that makes sense but why is pressure falling in the left ventricle I mean isn't it filling up with blood and doesn't filling it you know if it's filling up with blood doesn't that mean that you know pressure is rising that's sort of true but remember there's also another process going on so on the one hand on the one hand you have more blood and you're right that would definitely cause more pressure right that should cause more pressure but on the other hand remember you solve relaxation right you have another process going on the heart or the left ventricle is still relaxing all those muscles are repolarizing so that's going to cause a decrease in pressure so you have these two counteracting forces and for a very short time just for you know let's say from here to here this short period of time the pressure is actually falling because the relaxing winds out that's actually the bigger deal and so you have a decrease the left ventricular pressure because that last little bit of pressure that it was exerting goes away and finally when that goes away now you have nothing but filling so now you kind of slowly will fill it up more you know let's say to that level and then you'll fill it up more let's say to this level and you'll just keep filling all the way back up right so you'll kind of slowly fill back up and the pressure will just kind of keep rising in the left ventricle and similarly the left atrium because of course the there's a continuous space like we talked about between the two ventricles so now you can see that there's actually a third you can call it a wave but really it's just kind of a spike in a way right here which we call V and you can kind of remember that by saying well that's when the left atrium is very full so very full left atrium very full left atrium is what causes that last little spike and the fact that there's a quick drop office because that's when the mitral valve opens so let me actually box that so you can remember the three interesting parts of the left atrium pressure wave the a is when there's atrial systole so you have a little bump in pressure from the contraction of the muscle C is from blood crashing off of that mitral valve so that's really because of the left ventricle squeezing and of course all the the mitral valve snapping shut suddenly and then V is the very full left atrium right and one final thing I want to point out is that the middle one this C you know this is actually really quite similar to what we described happening with the dicrotic notch right similar idea because there we also had blood crashing off you had blood crashing off the aortic valve and there we talked about the compliance of the aorta so there's actually some similarities between the two but this is the left atrium pressure wave now