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Current time:0:00Total duration:10:51

Video transcript

so the main thing I wanted to do in this video is just kind of show you the timing of a heartbeat and we've been drawing the left ventricular pressure and so far I've kind of just sketched it out but now I want to try to be a little bit more careful with how I draw it so that you can get a real appreciation for for how long everything seems to take so these numbers I'm going to write up are are just estimates they're not exact numbers and of course you know that many things change how fast or slow a heartbeat can be but they give you a real sense for for the timing so let's get started the left ventricle it begins we know with a pretty low pressure right pretty low pressure let's say this is about 50 millimeters mercury I'm just going to estimate this is about 10 and we know that it's going to begin contracting and I'm just going to have to pick a point somewhere so I'm just going to kind of pick this point right here it begins contracting at a pretty low pressure about 10 millimeters of mercury let's say and right before it contracts the last kind of thing that happens remember is atrial systole and it's kind of a lump in the pressure kind of the pressure goes up and then it kind of slightly goes down and that's because of the atria contracting right and before that I'm kind of going backwards now you see that before that the atria and the ventricle are just kind of slowly filling up with blood and so the pressure is just kind of slowly creeping up so that's kind of the first step in terms of what the left ventricle pressure looks like it kind of creeps up and then has that little bump in the end now it has to go from that point to a very high point right when the ventricle contracts it's going to skyrocket in pressure let's say it's going to get up to around 80 or so and it doesn't take much time actually does it all in about 0.05 seconds it kind of just shoots up like that so kind of just skyrockets up so that's the next step right it kind of Rockets up and really let's talk about these two points real quickly these points here let's call this B and I'll call this a and so between a and B what's happening exactly well a the big kind of event at a is that the mitral valve closed so I'm going to write mitral closed and then of course at B the big event is that the aortic valve opened right so I'm going to write a or tick opened and you know when I write aortic I mean the valve not the artery because of course the aorta is just in order it's always open but the otic valve opened at that point now between those two and this is actually really kind of cool thing to think about between those two what's going on well here when the mitral valve closes to the point where the other one opens you've got a chamber the left ventricle with kind of a like a room with two doors that are closed right there's nothing open between these two spots where I've drawn the red and so because all of its closed we actually have a special name for this because there's contraction going on right the left ventricle is contracting so we call that contraction but because there's a room with two doors closed the blood has nowhere to go right so the volume of blood is not going to change it's going to be the same and the kind of medical word for that is ISO ISO means same so ISO volumetric same volume isovolumetric so contraction and all that means is that hey the left ventricle is contracting in oh by the way the blood volume is not changing because there's nowhere for the blood to go so kind of a fancy word but that's what it means so now the blood is going to start entering the aorta up here and it's going to really get kind of a high pressure right and we know that it's going to take a little bit of time for all that blood to go into the aorta in fact it takes about a quarter of a second and at the end of it we know that the pressure has to be or is going to be somewhere around a hundred it's going to be around 100 but my blood pressure is going to peak out somewhere higher than that somewhere around 120 in fact I know that because whenever I go to the doctors they always check my blood pressure and they tell me hey you know Rishi your blood pressures around 120 over 80 so this is this is helping me draw my my graph right so I can say well I know it has to get up to about 120 because that's what my my doctor told me it was and at some point it's going to kind of dip down again too this point and I'm drawing it at a hundred because we know that the aortic valve is going to close at some point and then of course you remember that hole dicrotic notch bit but that's kind of roughly what it might look like in fact let me actually just draw that with a yellow and the yellow just kind of reminds us that now at this point blood is entering the aorta so whenever this whole yellow bit is blood going into the aorta and of course you get to another important spot here and you remember let's call this spot see here the aortic valve closes so this is where the valve now kind of says hey enough is enough so let's shut down because pressure is kind of going the other way and then our blood pressure is going to fall right it's going to fall and it's going to fall over a bit of time it's actually can take about 0.15 seconds and it's going to go to about let's say I'm just kind of sketching it out let's say about here so about that point let's say and it's going to fall fall fall fall fall and why did I choose this point well that's the point where we say well this is where what happens what happens at this point the mitral valve mitral valve opens right the mitral valve open to that spot and then of course the pressure continues to fall right gets pretty low pretty low and then eventually has to kind of get back up to where we started right otherwise the next heartbeat is not ready to go so we have to kind of creep our way back up as the blood kind of fills in and we're done so this part right here this third segment what I'm going to kind of use green again you have the aortic valve is closed but the mitral has not yet opened right and so does blood have anywhere to go nope it's again it's stuck in a room so if the blood is stuck in the left ventricle and the left ventricle is relaxing then you can you better believe we're going to have a fancy word for it we're going to call that relaxation I guess not that fancy but the first part of it is I so same volumetric so same volume same volume isovolumetric relaxation and that's this part right here because again the blood has nowhere to go and the left ventricle is relaxing and the last chunk out here I'm going to do in kind of a different color blue let's say is where blood is slowly kind of just filling back into the left atrium and obviously since the mitral valve is open also the left ventricle so these are the four kind of segments right and you might think we'll wait a second what about that first segment I didn't color that that part in and what I'm going to do instead is I'm going to say well this was about let's say this is point zero point two right so I'm going to do the same thing over here I'm going to say okay what about the point one point two right that would be equivalent right I'm going to say blood pressure keeps rising and let's say we have our little atrial systole something like that so just to make it kind of continuous instead of kind of drawing two separate chunks I think this will prove to you that it's basically the same thing right so this is kind of getting ready for the next heartbeat but in terms of time you would agree that that's the same segment so then if I was to actually chunk it out this part right here I'm just going to kind of draw it on the timeline axis is about 0.5 seconds so this is about I'm going to try to draw it big I said 0.5 sorry point oh five seconds my mistake sorry so 0.05 seconds the next chunk right this bit right here is about 0.25 seconds so you could say about a quarter of a second is right there this is about a quarter of a second and then you've got the next chunk this is about 0.15 seconds and again these numbers are not super important but I just want you to get a rough sense of kind of simply the fact that this is actually not the same as the contraction bit right so it's a little bit longer to relax so just kind of get that intuitive feel for that and then finally this last bit this is kind of obviously the longest bit right this is just going on and on and on this is going to be about point holy cow it's long huh this is about 0.55 seconds and of course if you add up these four numbers if you add them all up they should add up to one right one second because the whole point is that this is all happening in about a second and that's if we assume of course that our heart rate is 60 beats a minute now that is not always true of course right certainly sometimes it's much faster than that but if we assume that just for the sake of kind of getting a sense for a feel for this stuff then this might be a rough estimate of how it might look right now one thing that I've always thought is kind of interesting when you look at this stuff you think okay well which parts are systole which parts are diastole and these two if you chunk them together if you add them up this makes up your systole so that's kind of a nice way of thinking about it and if you then add up the rest of it this whole bit right here this is your diastole remember we have talked about how the the fact that diastole is about two thirds of the time and systole is about one third of the time and you can see how that's basically true here right and now the final thing this is actually something I kind of always threw me off kind of confuse me a little bit is this chunk right here this chunk I'm always wondered why this isn't part of systole you know it certainly looks like it's part of the lump right or the the big mountain kind of drawing but the truth is that we have to remember that the left ventricle is relaxing during this time and diastole is all about relaxation for the left ventricle so because it's part of relaxation it is technically and truthfully part of diastole even though it looks like it's part of the lump so just keep that in mind