End systolic pressure-volume relationship (ESPVR)

by this point you may be getting kind of sick of these pressure-volume loops but I assure you they're very very worthwhile getting to know in fact let's learn one more thing out of these pressure-volume loop so let's try to squeeze all the knowledge we can out of these things so I'm going to draw one for you here very quickly and on this side we've got pressure in millimeters of mercury and on this side we've got milliliters right we're just going to use the same units we've kind of gotten very familiar with and we're going to do 50 and 100 and 125 or so on this axis that's a pretty normal set of terms or numbers and then on this side we've got 0 50 and I'm going to go up to 120 or so up here so this would be a pressure volume loop and I like to kind of start out where the pressures are low and the volumes are really really high so somewhere around here and I'm going to imagine that this is kind of the end of diastole where my heart is or my left ventricle rather is full of blood right and it's going to start rising in pressure slowly and as it rises it's going to get to let's say about this point and then the blood is going to start entering the aorta and as it enters a ORD I've got to get to a nice high pressure I know that that's the target or they're bouncing so the pressure kind of rises even higher and then the volume starts to fall as volume enters the aorta and so leaves the left ventricle and then the left ventricle continues to lose its blood to the aorta and the blood in the left ventricle that's left is around 50 and then you start having relaxation so you relax all the way down and the pressure Falls let's say to about that point and then it continues falling but now there's a little bit of blood kind of entering into the left ventricle so it's starting to fall in pressure but continues to this note let's now start rising in volume and it continues to rise until it's ready to do the whole thing all over again right and now if this is kind of our overall pressure volume loop what I want to do is kind of focus in on one particular point let's focus on this point right here and is the end of systole right talked about the end of systole being right here this is where it begins to start relaxing and when I say it I mean the muscle cells so you've got a muscle cell over here and I like to draw them kind of branched is to remind you that they're muscle cells and you've got now this cell completely contracted down right so it looks like this with the actin - and completely overlapping right because that's what you expect to happen at the end of at the end of systole and of course I'm drawing it this way really just to kind of remind you what's going on inside of the cell although you know that of course a cell has many many many sarcomeres not just one and of course this one I draw I'm just having one but you get the idea that there's a lot of overlap between the actin and the myosin in fact that's what these little red lines represent just the major proteins instead of hard cells so these are my heart cells full of protein and they're completely contracted right so sometimes they like to relax in sometimes I like to contract and at that end of systole where I've drawn that orange arrow these muscle cells are completely contracted down I'm going to write contracted just to current remind you that that's what's going on and what are they waiting for me what's next what are they hoping will happen next well they're hoping that they can now get rid of all that calcium and so they can relax so you've got a lot of calcium in this space and they're kind of hoping that the calcium will go away and they can relax and so imagine now that the calcium I'm going to draw calcium is a white circle right and I'm going to fill it in so this is my calcium right and imagine that I've got calcium in here I'm just going to draw a little white circles in here and instead of allowing my heart cell to to relax I'm going to kind of do something interesting and I remember calling it a trick last time I guess I can call this a trick and the trick is I'm going to trick my heart cell into not relaxing I will basically not allow it to relax because I load up this cell imagine I can somehow do this with lots and lots of calcium and so I just fill it with calcium it's chock-full of calcium and it has no way to really get rid of it so it is going to continue to be contracted right it's just going to continue to be contracted if I can somehow fill this with calcium and not allow it to go into relaxation so my heart cell is completely contracted that's the key right I have I have done this and so as a result of doing this now of course this won't happen this relaxation bit this won't happen and neither will the next bit so basically I'm kind of forcing myself to continue to remain contracted and all this kind of disappears and so what happens is that now my heart is basically full of blood right I've got a heart full of blood I'm going to draw it over here I'm going to just kind of ignore for the time being the left atrium and the aorta but this is my left ventricle full of blood so this is chock full of blood and what I'm going to do is I'm going to take a little needle watch this I'm going to take a little needle and I'm going to try to add a little bit of blood or take a little bit of blood away and I guess I'm going to start by taking a little bit of blood away just to just to see what will happen right so I take a little bit of blood away just to see what will happen and let me choose a different color let's choose a green color and at this point now my heart is again it's full of blood right and I'm going to now take a needle and I'm going to take some blood off of the heart I'm going to actually just pull it off like that so now I've got blood in my syringe and as a result what have I really done well I've lowered the volume right I've lowered the volume actually let me switch to a green color and show you that I've lowered the volume and if I lower the volume basically what will happen well if I lower the volume the pressure will start to fall right the pressure goes down so I go something like that and I could do this again and I could see if the pressure falls and oh it does and I could do this again in fact I could take all the blood out of the volume or out of the left ventricle and I could see that basically my pressure will go down to zero so I basically have now a few dots right I can connect my dots and I can see that I create this basically kind of a line right and so this line is what you would get if you just keep reducing and reducing reducing the volume in the heart now what if I did the opposite what if I instead of reducing the amount of blood what if I actually added blood and of course it might be kind of tricky to think by adding blood but just remember you can always add air to a balloon if you try hard enough and similarly you can actually push blood into a full left ventricle if you have enough pressure pushing down so I can actually do this I can actually try to do this in fact I'm going to add let's say a little bit of volume here right and I'm going to notice that the pressure goes up in fact it goes up even more than it ever did before right it actually rises above the line that I had drawn in blue and in fact I might even do it again I could say well let's just add some more volumes just to see what happens and the pressure goes up even higher so I could connect these lines or I could say okay well let's see what these lines look like and basically it's forming a nice straight line in fact to see it a little bit easier let me just get rid of the blue stuff let's get rid of all this stuff and you can see that you get this nice straight line that relates volume to pressure right and so this this relationship between volume pressure pressure and volume is happening with the muscle cells contracted remember all this time my muscle cells are bathing in calcium right they're completely contracted down they have not been able to relax they're contracted and so you could even say well this is basically the relationship between pressure and volume at the end of systole so you can say this is the end systole pressure volume relationship pressure volume relationship and this is kind of the long way of saying it people actually shorten all of this down they don't say all these words they usually say es you'll see this ESP VR and systolic pressure volume relationship and all it means is that if you could get a situation where your heart cells are completely contracted right completely contracted down and that's where I kind of made up the bit about you know filling it up with calcium because I guess that's one way to do it but you know completely contracted and you just kind of added volume or took it away what would the pressure do what you know how would it change and this line tells you that in fact one final kind of point I want to make about this is if you remember there's a relationship now between elastance remember the term elastance and pressure and volume in fact if you take pressure divided by volume that gives you elastance so with this line that we've drawn you can actually say well there's a slope to this line right this is I'm draw kind of a straight line so there's you know imagine there's a straight line between all these points right well the slope of that line slope is elastance right that is the elastance in fact you might even see the the term you know wherever the wherever the pressure-volume loop falls on this ESP VR sometimes even see the line actually labeled and you see it called Enon in fact so you'll you'll often see that so II not refers to the slope of the line that is formed at the end of systole