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Current time:0:00Total duration:9:01

Video transcript

so this is our left ventricular pressure curve and I've divided into four sections and actually I've chunked in this extra bit here this is actually kind of going to the second heartbeat and the reason I did that remember is because I wanted to make sure that you can see the entire last chunk of the heart cycle is blue bit instead of having to kind of try to remember adding this part in so just to keep it easy on the eyes I just kind of went into the next heart beat to make you kind of see very easily that this is all one part of the cycle in a sense now instead of looking at pressure what I want to do is actually kind of look at volume and so when I'm going to do is I'm actually going to draw out the same axis right so we're going to have time using seconds over here and I'm going to kind of follow the heart specifically the left ventricle in the same way I was following it before kind of in four sets right this is like let's say one point two seconds this could be one second this could be 0.75 and this could be 0.5 and this could be 0.25 right something like that if there we go and on this side I'm going to do volume so volume in milliliters and we're going to start with zero down here and we'll do 50 right there let's do a hundred and 125 and these numbers I'm actually just kind of choosing because I think there are reasonable numbers but of course we know that these numbers can change person to person now to figure out what is happening over time I'm actually going to label the four points as before where the color is kind of changed on our graph ABCD and we know that going from A to B this we called isovolumetric contraction isovolumetric contraction meaning kind of the the volume in the heart stays the same while there's a contraction going on there and on the other side in green we have isovolumetric relaxation so kind of the same idea that volume is not changing during these times and because of that I think that's kind of an easy place to start our graph so we're going to use a B C and D for isovolumetric contraction and relaxation now when we're talking about contraction you know that at this point the heart the left ventricle is really full of blood right when it's about to contract it's as loaded up as it's going to be and so these are the two points a and B right and then for C and D you basically have blood kind of what's residual in the heart and that let's say is around 50 so these numbers 125 and 50 I've chosen them because again they're reasonable numbers but it could definitely change person to person and I really just want you to kind of get a sense for the the overall pattern what it kind of looks like so these two parts of our graph I'm just kind of sketching out like that and in fact I can even draw that last a right because it gets into the next heartbeat to be somewhere like that that's kind of resetting and restarting the next heartbeat so the question is you know what is the slope of the line here you know is it just kind of a linear thing like that is it just a line or blood kind of fills in something like this or is it something a little bit different from that and to answer this question I think it really is helpful to revisit that old equation Delta P equals Q times R something like that right and in fact I'm actually going to blow up two sections of the curve I'm going to blow up one section like this and I think you'll recognize which sections they are just based on the color and the shape I'm drawing them in another section like this all right so we've got two sections and actually maybe the slope is not quite like that and it looks maybe like this so there are two sections here right the way to kind of apply this idea Delta P equals Q times R what I want you to do is think about this think about section one which is right here in section two separately this is section one and this is section two and what's happening in terms of the aortic pressure drink section one well they order is of course kind of coming in like this and it you know immediately they order valve opens and then quickly the pressure rises and it rises and then finally kind of catches up with the aortic pressure or the left ventricular pressure and then at some point let's say right here it's going to kind of do this and have that dicrotic notch we talked about and on the bottom this is of course the aortic pressure right and on the bottom we've got left atrial pressure to think about so left atrial pressure is kind of coming in like this and it's rising quickly and it's maxing out remember it's very full we said and then it kind of begins to fall right it begins to fall and then it kind of picks up again so these are the kind of curves that you get for the left atrium left atrium and the aorta why did I draw this out why did I make it all big like that well because if we're talking about Delta P all that means is the difference between the yellow line and the white line that's all it is Delta P difference in two pressures so if I look at this it's actually kind of a nice difference kind of a good size difference if I look up here it's kind of a medium size difference and if I look over here there's almost no difference right so Delta P is starting big and getting small right so Delta P is getting smaller and smaller with time and over here it's kind of a similar situation starts out big and then it gets kind of medium and then it goes eventually kind of small so it starts out big and then eventually gets smaller so whenever you see Delta P change and pressure and you see two pressure lines that's kind of an immediate that's an easy one in a sense right you just have to look at the difference between the two lines so how does that help us well you can see that Delta P equals Q times R and what is Q exactly well Q remember this is flow blood flow and the units on Q and this is going to kind of maybe you'll have an aha moment I did when I first thought about this the blood flow is simply volume over time right and if you have volume over time then that's nothing more than the slope of the line the slope down here on this line is going to be volume over time right so if I can show differences in Delta P and I guess here we have to I have to state my assumption my assumption is that resistance isn't changing much so this is kind of basically steady this is basically steady within the heart within the heart it's not there's not huge changes in resistance from heartbeat heartbeat within the heart we don't assume that so really if you can see a change in Delta P then you'll see a change in flow and that's exactly what happens right so initially we said that there's a big Delta P over here right a big Delta P with aortic pressure so that's kind of looking at this point right here and that means that there's going to be a big flow that there's a lot of blood flowing in this case out of the heart and then there's a lot of blood flowing out of the heart then that means that this line the slope of the line is going to be really steep and negative and then eventually you get kind of a small flow right eventually the the Delta P kind of becomes tinier and the flow becomes less significant so that you get a smaller flow so you get basically something like that so instead of that white line the truth is that you got something that looks more like that yellow line now what about the other side going from D to a well going from D to a let me just switch colors here you have a similar situation you've got kind of a big Delta P initially right a lot of blood flowing this time into the left ventricle so it kind of rises quickly and then eventually it kind of gets smaller over time right so eventually it's going to kind of do this and that's why on the other side we have to kind of change that white line as well so this white line over here is going to change as well and it's going to look more like that it's going to look more like that so this is exactly what the volume time graph looks like it kind of has this interesting shape and instead of just kind of having you memorize a shape I want you to understand where it comes from so there you go