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I want to talk a little bit
about the idea of pressure

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and volume.

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00:00:05,630 --> 00:00:07,560
And we're actually
a clear up some

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misconceptions I think
I may have caused.

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I apologize for them.

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But I think this is
a good chance for us

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to reflect on the things
that we've learned

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and also build up a
couple of new ideas.

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So let's draw volume going
that way and pressure going up.

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And one of things I
want to start with

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was the end systolic
pressure volume relationship.

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We drew it something like this.

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So we said this is
the relationship

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at the end of systole
between the two,

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between pressure and volume.

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And one thing that I wanted
to bring up immediately

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was the idea of
increasing volume.

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So as I go up to this yellow
line, I'm increasing volume.

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And sometimes the way I've
drawn that-- actually maybe I'll

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make a little bit of
space on this canvas.

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And sometimes the way I
draw an increase in volume

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can be a little bit misleading.

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So I've drawn, for
example, in the past,

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I've drawn a left
ventricle like this.

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And I said well as blood
goes into my left ventricle,

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it basically does this.

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You have more and more
blood filling up the heart.

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And I've drawn this
sort of a picture,

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and it really does tell
you about a couple things.

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It tells you that you
have filling happening.

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And that part, I'm OK with.

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But the part that
I'm not OK with

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is the idea that
it basically seems

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like you have a fixed volume.

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It looks like a fixed
volume on the heart,

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or the left ventricle anyway.

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And it almost makes
it look like you're

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filling up a glass of water.

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Basically, that's kind of
what it looks like a glass.

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And really the correct way to
think about left ventricular

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filling is a little
bit more like this.

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You should be thinking of
it more along the lines

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of a picture like this
where you basically

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have a smaller volumed the
left ventricle filling up

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with blood.

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And over time it kind
of feels in completely.

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So it starts out like that.

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And then you add more blood
and it becomes like that.

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And then you finally
fill it up like that.

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So that would be the
more accurate way

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of showing what's going
on in the left ventricle.

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And, of course,
all three of these,

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then, are the left ventricle
at different points in time.

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So this second picture also
tells you about filling,

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so you get the idea that
blood is filling in the heart.

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But it does a better
job of showing you

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that the volume changes.

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The volume of the left ventricle
changes, so it's not fixed.

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And that's correct.

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This is the better
way of looking at it.

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And kind of an analogy
might be a balloon,

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you might think of a balloon
for this filling process.

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So I want to be very clear
that the left ventricle is not

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like a glass.

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It's like a balloon.

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And that it's not
a fixed volume.

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It actually changes.

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So this is probably the more
accurate way of thinking about.

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And I apologize for doing
this sort of a drawing.

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Truthfully, I didn't
mean to confuse anyone,

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but I just want to
demonstrate filling.

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And I probably just do it
in a quick and hurried way.

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And so I want to
clarify that point now.

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So this is what it
would look like.

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And actually I could
take this a step further

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and say well what
if I was to do this?

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What if I was to take a
cross section like that,

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cut it with a blade at
these three points in time?

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Wouldn't you agree
that you would actually

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get an interesting cross
section view of it,

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if I was to take
it like that and I

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was to erase these top bits out.

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And you were to now
look down at the heart,

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you'd basically see kind
of an interesting view.

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And I'll actually try to
draw that view out for you.

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And it's helpful actually
to do it that way.

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And I'll tell you why So
this one would basically

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look like this.

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And this one would
look like this.

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And this one might
look much larger

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than the other two
something like this.

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And again this is just
looking at a cross section,

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so it's nothing
different at all.

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It's just looking at
the cut surface of it.

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And all three you'd
expect to be full.

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So this is how I'm going
to use our diagram.

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I'm actually going to
use these kinds of images

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now to show what filling of
the left ventricle looks like,

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so we can actually get
a real sense for it.

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And you'll see an interesting
problem that comes up.

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So let's do that.

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Let's draw a couple
of circles here.

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I'm going to draw, let's
say, a big circle here

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where it's really large.

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And then let's say the volume
is little small at this point.

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So let's draw
something like that.

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And the volume is
really, really tiny.

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Let's draw something
like that over here.

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Now if you have these three
volumes, you might say,

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well, OK you've colored them in.

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Well, one thing
you'd have to admit

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and you'd realize pretty
soon is that at the bottom

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of this curve, you
have a small volume,

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but it does take a little bit
of blood to fill that volume in.

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When you have zero
volume-- like right

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here there's zero
blood in there--

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it would be an empty
left ventricle.

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And then you'd actually add
a little bit of blood to it.

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Let's say you fill it up.

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Let's say halfway.

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And now you've got a
half full ventricle.

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And then you keep doing it
and you have a full ventricle.

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So you basically are going
this way along the curve.

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But until you have
a full ventricle,

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and this is the point, until
you have a full ventricle

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you actually don't have
any increase in pressure.

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So previously when I drew
out the end systolic pressure

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volume relationship
with that yellow line,

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I drew it the way
you see it now.

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But now I'm telling you that
the truth is that it actually

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looks a little bit
different, especially

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at the bottom end of this curve.

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So I'm going to erase this
and draw it in properly.

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And this is the more accurate
way of drawing it in.

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You basically have
almost no-- or really no

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increase in pressure.

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I shouldn't say almost no.

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And then once you get
to a full ventricle,

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now you start seeing an
increase in pressure.

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And really the way that an
increase in pressure looks

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is that you have
a larger volume.

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And that's what you're
starting to see.

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You're start to see
that larger volume.

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So even a tiny
bit of pressure is

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going to push out on
the left ventricle.

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And you'd actually notice that
because now it gets larger.

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So the left ventricle actually
doesn't change in size

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initially.

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And, finally, when the pressure
starts actually mounting up

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it starts changing in size.

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So you can start
appreciating why

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I am saying that this first
yellow line is incorrect.

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Let me erase it completely
so it doesn't distract you.

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So I've drawn out the end
systolic pressure volume

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relationship, but what I
want to do is now add to it

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our end diastolic pressure
volume relationship.

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We know it goes
something like that.

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And let me just label
it in a yellow color

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just to be parallel.

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So this is our end diastolic
pressure volume relationship.

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Now if I was to say, well, what
would the cross section look

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like?

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Now let's just kind of
choose a couple points

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to say this is this point.

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This is this point like that.

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And if I said what would
the same volume look like

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on the other curve, I
would have to actually

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just draw a line
down and say, OK.

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This is this volume right here.

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And this is this
volume down here.

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And along those
points-- let me ask

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you just mark it
on my other curve.

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Those points would
be right there.

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And I actually could just
similarly draw them out.

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I could say well
this is about that.

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And then the other one looks
maybe a little bit larger.

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It would be something like that.

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So these are my two curves.

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Right?

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Now I'm trying to make them
look as similar as possible

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to the other ones.

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And I'll fill them in.

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So that's what the volumes
would look like at these points.

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So really when you
look at the volumes,

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they look about the same.

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They don't look any
different at all.

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And so you're left wondering
well how in the world is it--

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and this is actually very,
very confusing to think

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about for folks-- how
in the world is it

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that the pressure is so darn
high on the end systolic curve

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whereas it's low on the end
diastolic curve, when they look

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the same?

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They don't look any different.

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And to figure this out-- I think
one easy trick I've been using

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is to just imagine what's
happening at the muscle level.

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So the muscle cells are kind
of contracting and pulling

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in those z-disks.

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At the end of systole, we've got
tons of contraction happening.

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And it's happening here too.

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In fact, it's happening at
every part of this curve.

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And if I was to try to simplify
this, instead of drawing

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00:08:40,900 --> 00:08:42,799
hundreds of arrows
like this, I could

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do this for every single point.

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So instead of drawing
hundreds of arrows,

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you could imagine
that I can actually

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connect all these
arrows like this

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00:08:50,060 --> 00:08:52,480
and that I would have a
similar effect if I just

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drew it like this.

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00:08:53,910 --> 00:08:57,040
I could simply draw almost
like a rope or a band--

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imagine a band or rope
that's pulling and tugging

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00:09:01,290 --> 00:09:03,900
this way and this way.

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00:09:03,900 --> 00:09:06,130
If I was actually to
draw the band like that,

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00:09:06,130 --> 00:09:08,280
you could imagine then, it
would be the same effect

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00:09:08,280 --> 00:09:11,590
as the hundreds of little
muscles that are contracting.

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00:09:11,590 --> 00:09:13,430
And to take it a
step further, you

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00:09:13,430 --> 00:09:16,440
could actually even imagine
people yanking on that band.

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00:09:16,440 --> 00:09:18,840
So this is how I
picture it, just

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00:09:18,840 --> 00:09:21,300
people yanking on that band.

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00:09:21,300 --> 00:09:22,720
These are like two
little workers,

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00:09:22,720 --> 00:09:26,175
let's say, yanking on
the band and pulling it

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00:09:26,175 --> 00:09:27,520
in opposite directions.

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00:09:27,520 --> 00:09:29,645
And if they were pulling
it in opposite directions,

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00:09:29,645 --> 00:09:32,150
you basically have what we
think of as contraction.

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00:09:32,150 --> 00:09:33,860
You could have
little workers that

225
00:09:33,860 --> 00:09:37,800
are basically yanking on all
these things, yanking away.

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00:09:37,800 --> 00:09:40,400
And by yanking away, what
you basically end up with

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00:09:40,400 --> 00:09:43,380
is a force of contraction.

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So this is basically how
I imagine contraction,

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00:09:46,100 --> 00:09:48,620
having workers yanking in
two different directions.

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And if you had them going
all around the heart

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00:09:51,120 --> 00:09:53,300
in every direction you
could possibly imagine,

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00:09:53,300 --> 00:09:56,270
that is what a contracted
ventricle is like.

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00:09:56,270 --> 00:09:59,230
And because they're
yanking so darn hard,

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because they're pulling
so hard on this thing,

235
00:10:02,110 --> 00:10:03,930
you basically have
a lot of increase

236
00:10:03,930 --> 00:10:07,974
in pressure building up on the
inside of these ventricles.

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00:10:07,974 --> 00:10:10,390
And you really don't have that
happening on the other side

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00:10:10,390 --> 00:10:13,730
because on the end
diastolic curve--

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00:10:13,730 --> 00:10:15,980
I guess the question is
do we have any workers?

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Are they yanking?

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00:10:16,780 --> 00:10:18,350
And the answer is no.

242
00:10:18,350 --> 00:10:20,860
The muscle cells are
completely relaxed.

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00:10:20,860 --> 00:10:21,940
They're relaxed.

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00:10:21,940 --> 00:10:25,390
They're just hanging
out and taking a nap.

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00:10:25,390 --> 00:10:29,090
You can imagine your workers
are really not yanking at all.

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00:10:29,090 --> 00:10:31,372
And as a result,
you don't have any

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00:10:31,372 --> 00:10:32,580
of that increase in pressure.

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00:10:32,580 --> 00:10:35,940
You have just a very,
very low pressure.

249
00:10:35,940 --> 00:10:37,789
And so that's the
reason you can imagine

250
00:10:37,789 --> 00:10:39,830
there's a difference, even
though the volumes are

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00:10:39,830 --> 00:10:42,450
the same, that there's a
difference in pressure.

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00:10:42,450 --> 00:10:45,010
So final question that plagues
a lot of people-- and I'm

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00:10:45,010 --> 00:10:46,843
actually going to make
a little bit of space

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00:10:46,843 --> 00:10:51,224
to answer it-- is so why is
their blood in the ventricles

255
00:10:51,224 --> 00:10:52,140
at the end of systole?

256
00:10:52,140 --> 00:10:54,910
I mean isn't that the point
where all of the blood

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00:10:54,910 --> 00:10:57,596
has exited the ventricles
and gone into the aorta?

258
00:10:57,596 --> 00:10:59,220
Why is there any
blood in there anyway?

259
00:10:59,220 --> 00:11:00,990
Shouldn't it be empty?

260
00:11:00,990 --> 00:11:03,390
And to answer this--
to think about this,

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00:11:03,390 --> 00:11:05,560
we can actually draw a
pressure volume loop.

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00:11:05,560 --> 00:11:07,310
I'm just going to
draw it in purple just

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00:11:07,310 --> 00:11:09,570
to create a little
difference in color.

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00:11:09,570 --> 00:11:12,260
And let's say that
I have contraction

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00:11:12,260 --> 00:11:14,230
right here where I
have a big purple dot.

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00:11:14,230 --> 00:11:15,970
That's where I begin
my contraction.

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00:11:15,970 --> 00:11:19,740
So I'm going to draw going
up from there like that.

268
00:11:19,740 --> 00:11:24,090
And let's say now my
ejection is happening.

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00:11:24,090 --> 00:11:27,860
And let's say, just rides
over my picture of the worker

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00:11:27,860 --> 00:11:28,560
like that.

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00:11:28,560 --> 00:11:32,500
Let me actually draw
one final volume piece,

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00:11:32,500 --> 00:11:34,710
and that would be what
is the volume here.

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00:11:34,710 --> 00:11:37,020
Because we know that the
volume is not changing there,

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00:11:37,020 --> 00:11:38,540
it's constant volume.

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00:11:38,540 --> 00:11:41,490
And at this point,
you begin ejections.

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00:11:41,490 --> 00:11:44,240
So this is all ejection.

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00:11:44,240 --> 00:11:48,370
I'm going to write ejection on
the curvy part of the curve.

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00:11:48,370 --> 00:11:51,950
So this is ejection
happening right here

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00:11:51,950 --> 00:11:53,500
over the hump like that.

280
00:11:53,500 --> 00:11:56,500
So ejection is happening
between my two white lines.

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00:11:56,500 --> 00:12:01,500
And here in the vertical part, I
could draw a picture like this.

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00:12:01,500 --> 00:12:04,330
I could say, well, my
heart will be really full.

283
00:12:04,330 --> 00:12:06,677
So it'll look-- in fact,
let me make it bigger.

284
00:12:06,677 --> 00:12:08,510
My heart is going to
be really, really full.

285
00:12:08,510 --> 00:12:10,970
Let me try to
illustrate that nicely.

286
00:12:10,970 --> 00:12:13,080
So I could have
something like this.

287
00:12:13,080 --> 00:12:15,780
I could have
something like that.

288
00:12:15,780 --> 00:12:19,740
And if my ventricle is that
big, if it's that large-- let

289
00:12:19,740 --> 00:12:21,780
me actually just
color it in now.

290
00:12:21,780 --> 00:12:25,360
Then what's actually happening
when I have ejection?

291
00:12:25,360 --> 00:12:29,250
Well, I'm going to cut
and paste this little guy,

292
00:12:29,250 --> 00:12:33,580
and show you on the top
what it would look like.

293
00:12:33,580 --> 00:12:36,410
So let me just drag this
little fella over here.

294
00:12:36,410 --> 00:12:41,110
And now this, if this
is how I start out,

295
00:12:41,110 --> 00:12:43,714
then when I eject
blood, you're basically

296
00:12:43,714 --> 00:12:45,130
going to have
something like this.

297
00:12:45,130 --> 00:12:49,210
You're going to have an
amount that goes away,

298
00:12:49,210 --> 00:12:50,820
and an amount
that's left behind.

299
00:12:50,820 --> 00:12:54,030
So the amount that's left
behind is, of course, the amount

300
00:12:54,030 --> 00:12:57,580
that I showed you on the side.

301
00:12:57,580 --> 00:12:58,880
And I'm cutting it out.

302
00:12:58,880 --> 00:13:01,080
And this doughnut hole
shape that's left,

303
00:13:01,080 --> 00:13:03,620
this is actually
our stroke volume.

304
00:13:03,620 --> 00:13:05,810
This is our stroke volume.

305
00:13:05,810 --> 00:13:08,930
So you actually do have a lot of
blood that goes into the aorta.

306
00:13:08,930 --> 00:13:11,340
Of course, that's important.

307
00:13:11,340 --> 00:13:13,690
And you have a little
chunk that's left.

308
00:13:13,690 --> 00:13:18,220
So now you can see that at
the beginning of contraction,

309
00:13:18,220 --> 00:13:21,450
you end up with having
a lot of blood here.

310
00:13:21,450 --> 00:13:23,220
This is where you start.

311
00:13:23,220 --> 00:13:25,210
And then you lose
a lot of blood.

312
00:13:25,210 --> 00:13:27,070
This is our stroke
volume that you lose.

313
00:13:27,070 --> 00:13:29,660
And then you are left with
a little bit of blood here.

314
00:13:29,660 --> 00:13:32,540
And that's at the end of
systole So at the end of systole

315
00:13:32,540 --> 00:13:35,510
you do have some blood left, but
you don't have nearly as much

316
00:13:35,510 --> 00:13:38,520
as you had when
you began systole.