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Current time:0:00Total duration:9:58

End diastolic pressure-volume relationship (EDPVR)

Video transcript

let me draw out the pressure-volume loop I'm going to just start out something like this and it's really easy to try to draw a pressure-volume loop from scratch that's one of the reasons I love about it one of the things I love about it rather got pressure on this side and we're going to do it in millimeters of mercury which is pretty typical for us right we've got 0 to 100 and let's just make this 120 up here and this can be 50 and on the volume side let's make this 100 over here that makes this about 50 and I'll make this about 125 right and I like to start out with kind of low pressure and high volume that's the you can start out anywhere in the loop really right but I just like to always start out right here with a blue dot and that's the point where the heart the left ventricle specifically in the heart is full of blood and it's going to start squeezing right it's going to start contracting so pressure is going to go straight up and it's going to keep rising rising rising to about let's say here and I hope that was a straight line it's about around 80 or so and then the blood starts getting into the aorta right because the aortic valve flips open at that point and so it starts losing volume because the the blood volume is actually heading into the aorta and then the the volume continues to fall and the pressure begins to fall and so it looks something like that and that blue line that I drew so far that is systole right that's systole so that's the part where the muscle is contracting or the heart muscle is contracting and then you have the next part of the pressure volume loop where now you have relaxation so you have a fall in pressure to about there right and then you have a continued decrease so it continues to go down let's say to about there and this is now where blood is entering the left ventricle which is why I'm showing it going up in volume and you finish your loop something like that so this is your pressure volume loop now I'm going to zoom in on let's say a heart cell just to kind of point out what's going on at the heart cell level and remember heart cells are often branched so I'm just going to draw it that way and let's show some actin and myosin of course I'm kind of exaggerating what it looks like just to kind of make the point but you might have something like this right lots of actin and myosin inside of these cells and remember these cells now I'm just kind of reviewing with you have a nucleus here maybe a second nucleus there but they're full of actin and myosin it doesn't look exactly the way I drew it but I just want to remind you that there is a lot of protein inside those cells and the thing that these cells are waiting for is calcium right the moment calcium enters these cells then they can contract and if they contract then you basically have this part occurring in fact also this part occurring right this is all contraction so all this contraction is happening with the assumption that calcium is coming inside of those cells so what if I decide to play a little trick and I basically somehow I vacuum up all the calcium and I don't let that calcium enter the cell well what would happen well you know you might have a loop but the moment I start doing this then you don't really have contraction anymore right so all of a sudden at this point I'm going to just kind of erase it you don't allow any more contraction so you wouldn't have this sharp increase in pressure in fact you would have any of this right if I could actually vacuum up all the calcium you wouldn't have any of that systole really happening you'd be basically kind of stuck in diastole so you'd basically be stuck here right and this is remember this point we used to call end diastolic and diastolic so when you get to that end diastolic point instead you'd be basically kind of stuck in limbo right now what if I took it one step further and I said well I'm just going to make a little space here by erasing all this what if I now draw for you the heart let's draw the left ventricle out like that and I'm not going to draw the the left atrium and just the left ventricle and I'm going to fill it in to look something like this right so you've got lots of blood inside of that that chamber of the heart right it's full of blood and let's say now that it's full of blood and it's not contracting I got to do something with with the left ventricle and I decide to kind of continue my experiment and I say okay I'm going to take an injection and I'm going to inject this left ventricle full of blood I'm going to put more blood in to the left ventricle I'm going to put more blood in and you might be thinking well how in the world do you put more blood into something that is full if it's full it's full right so how can you put more blood in well think of it like a balloon you can have a full balloon but if you put enough pressure you can actually increase the volume right so in this case it will take pressure and you know I'm not going to you know candy-coat this this will take work but if you're willing to do it you could actually put more blood into a full ventricle so let's extend this out let's say I put some extra volume in right like that well my pressure will go up a little bit and my curve will look like this let's say I extend this out it'll start looking like that and I could actually do it again I could put more volume in there and this time it took actually a little bit more effort because it's getting harder and harder not unlike a balloon right it's looking like that and I could do it again I can say well let me try one more time and now it's getting even harder right even harder to do this so my curve is kind of looking a little bit more like this more steep as time goes on so on the one hand I'm adding more volume that's what all these V's are but as I do that the pressure is going up that's what these Peas are so pressure and volume are of course related right and we could do the reverse I could actually flip it around and say well hold on a second instead of adding blood instead of adding blood what if I decide to take blood away what if I want to do something like this when I actually pull blood away off of the heart suck it back and take it and maybe throw it down the sink then what would happen well let's say I start at the same end diastolic point just to kind of make it nice and clear well if I was to do that if I was to take blood away then my volume of course would go down and if the volume goes down the pressure goes down and then I can do it again I could take more volume away and the pressure would go down and actually it would look pretty much the same as that chunk of our pressure volume loop so you can actually see now when we have our pressure volume loop that's actually kind of showing you what it would look like to fill up the heart and it makes perfect sense right as you as you change the volume of course the pressure will fall a little bit if you take more volume away the pressure will fall even more but what if I kept doing it you know what if I just kept extending this out and taking more volume off taking more volume off well the pressure would go down a little bit and I could do it again I could take even more volume off and I could end up with really no blood in my chamber and I would have of course no pressure at that point so you can actually connect these lines you can say okay well this is kind of what the curve might look like right something like that and of course I would have to erase this a little chunk because that was not related to passive filling right I always remember where the heart was still or the left ventricle is still relaxing and I can also just erase all this stuff to make our line more clear and easy to see and so now you see what you see emerging is a fantastic relationship right a pressure volume relationship and this pressure volume relationship is assuming that the left ventricle muscles are relaxed right this is assuming that there is no contraction happening so if remember my first assumption which was around getting rid of that calcium if you can really fully relax these cells if they're relaxed and then you kind of passively fill them up with blood or take blood away like I've done with my injection my needle then you develop this interesting pressure-volume curve so this is a pressure volume relationship pressure volume relationship and you might actually see all this kind of shortened down sometimes people don't have the time to say well it's the end Stalag pressure-volume relationship they have you know that's five long words so instead they might just say well this is your IDI P V R you might see that IDI PVR and you know one final point I want to leave you with is remember anytime you see pressure divided by volume that's really a slope of a line right so this could be the slope of the line right there or you can have the slope of the line right there so anytime you have P over V that's just a slope and that slope equals the elastance remember the concept of elastance elastance is just the slope of the line so if you ever want to think about it differently you could say well really the end diastolic pressure volume relationship line is also telling you a little bit about the elastance of the left ventricle of the left ventral when it's relaxed when it's relaxed so I'll leave you there and you can think about this a little bit more on your own