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

So the main thing I
wanted to do in this video is just show you the
timing of a heartbeat. And we've been drawing the
left ventricular pressure. And so far, I've
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 how
long everything seems to take. So these numbers I'm going to
write up 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 the timing. So let's get started. The left ventricle--
it begins, we know, with a pretty
low pressure. Let 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 have to pick
a point somewhere, so I'm just going to 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 thing that happens, remember, is atrial systole. And it's a lump in the pressure. The pressure goes up, and
then it slightly goes down. And that's because of
the atria contracting. And before that-- I'm going
backwards now, you see that? Before that, the atria
and the ventricle are just slowly
filling up with blood. And so the pressure's
just slowly creeping up. So that's the
first step in terms of what the left ventricle
pressure looks like. It creeps up and then has
that little bump in the end. Now, it has to go from that
point to a very high point. When the ventricle
contracts, it's going to skyrocket in pressure. And let's say it's going to
get up to around 80 or so. And it doesn't take much time. It actually does it all
in about 0.05 seconds. It just shoots up like that. So it just skyrockets up. So that's the next step. It 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, the big 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. So I'm going to
write aortic opened. And you know when
I write aortic, I mean the valve,
not the artery, because of course, the
aorta is just an artery. It's always open. But the aortic valve
opened at that point. Now, between those two--
and this is actually really a 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 room with two doors that are closed. There's nothing open
between these two spots where I've drawn the red. And so because all
of it's closed, we actually have a
special name for this because there's
contraction going on. 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. So the volume of blood
is not going to change. It's going to be the same. And the medical word for that
is "iso." "Iso" means same. So isovolumetric, same volume. So contraction. And all that means is that
hey, the left ventricle's contracting. And oh, by the way,
the blood volume is not changing, because there's
nowhere for the blood to go. So 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 a high pressure. 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 is going to be
somewhere around 100. 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 doctor's, they always check
my blood pressure. And they tell me, hey,
Rishi, your blood pressure's around 120/80. So this is helping
me draw my graph. So I can say, well, I know it
has to get up to about 120, because that's what my
doctor told me it was. And at some point, it's going
to dip down again to this point. And I'm drawing it
at 100, because we know that the aortic valve is
going to close at some point. And then, of
course, you remember that whole dicrotic notch bit. But that's roughly what
it might look like. In fact, let me actually
just draw that with a yellow. And the yellow just reminds
us that now, at this point, blood is entering the aorta. 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 C. Here, the aortic valve closes. So this is where the valve now
says, hey, enough is enough. Let's shut down,
because pressure is going the other way. And then, our blood
pressure is going to fall. It's going to fall,
and it's going to fall over a bit of time. It's actually going to
take about 0.15 seconds. And it's going to go
to about, let's say-- I'm just 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 opens. The mitral valve
opens at that spot. And then, of course, the
pressure continues to fall. It gets pretty low,
and then eventually it has to get back up
to where we started. Otherwise, the next
heartbeat is not ready to go. So we have to creep our way
back up as the blood fills in, and we're done. So this part right here,
this third segment, where I'm going to
use green, again you have the aortic valve is
closed, but the mitral has not yet opened. And so does blood
have anywhere to go? Nope. 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 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 "iso," same, volumetric. So 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 a different
color-- blue, let's say-- is where blood
is slowly just filling back into the left atrium. And obviously, since the
mitral valve is open, also the left ventricle. So these are the four segments. And you might think
well, wait a second. What about that first segment? I didn't color that part in. And what I'm going to do
instead is I'm going to say, well, let's say this is 0.2. So I'm going to do the
same thing over here. I'm going to say what
about the point 1.2? That would be equivalent. 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
continuous instead of drawing two
separate chunks, I think this will prove to
you that it's basically the same thing. So this is 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
actually to chunk it out, this part right
here-- I'm just going to draw it on the timeline
axis-- is about 0.5 seconds. I'm going to try to draw it big. I said 0.5, sorry. 0.05 seconds. My mistake, sorry. So 0.05 seconds. The next chunk, 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 get a
rough sense of simply the fact that this is actually not the
same as the contraction bit. So it's a little
bit longer to relax. So just get that
intuitive feel for that. And then finally, this last bit. This is obviously
the longest bit. This is just going
on and on and on. This is going to be about-- holy
cow, it's long-- 0.55 seconds. And of course, if you add
up these four numbers, if you add them all up, they
should add up to 1 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. Certainly sometimes it's
much faster than that. But if we assume that,
just for the sake of getting a sense or
a feel for this stuff, then this might be a rough
estimate of how it might look. Now, one thing that I've always
thought is kind of interesting. When you look at this
stuff, you think, OK, well, which parts are systole and
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 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. And you remember, we
have talked about how the fact that diastole is about
2/3 of the time and systole is about 1/3 of the time. And you can see how that's
basically true here. And now, the final
thing-- this is actually something that
always threw me off, confused me a little bit--
is this chunk right here. I've always wondered why
this isn't part of systole. It certainly looks
like it's part of the lump, or the
big mountain 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.