WEBVTT

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So here we are.

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We have our two
lungs and the heart.

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I'm just going to
quickly label stuff.

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We've got our right and left
lung, and we've got our heart.

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And I want to make
sure I label all

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of the four chambers
of the heart.

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I've taken away a
lot of the vessels.

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I just want to focus
on a couple of things

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here-- mainly, the blue
blood vessel coming off

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of the heart-- the one I've
drawn in blue-- which I'm

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going to label here as
the pulmonary artery.

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Remember, again, arteries
go away from the lungs.

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So this is our pulmonary
artery, even though it's

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got deoxygenated blood in it.

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A little counterintuitive,
but I think you got it now.

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So this is our pulmonary
artery, and it's

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going to the left
and right lungs.

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And if we assume that there's,
let's say, 5 liters of blood

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flowing through the
heart per minute,

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that means that 5
liters are going

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to go through this vessel.

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And some of that is
going to go to the right,

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and some is going
to go to the left.

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Let's say I told you that
2 and 1/2 liters goes

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to the left lung per minute.

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Let's just assume that.

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Then you know that
the other half

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of that 5 liters-- the rest
of it, 2 and a 1/2 liters--

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must also go to the right.

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Because whatever
goes into this tube--

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almost like a straw--
on one end has

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got to come out
on the other end.

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So you just, basically,
add up what's exiting.

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And it's got to equal
what's entering.

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So here we have
the idea of flow.

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And we've talked about
flow in other videos,

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but basically, I just
want to restate it.

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It's a volume over
a period of time.

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And in this case, we're
using liters over minutes.

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But really any kind of
volume over time you

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could describe as blood flow.

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Now, let's say that a
tragic event occurs,

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and I end up having
a surgery to my lung.

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Let's say underneath
this yellow line

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is my lower lobe and
above it is my upper lobe.

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Let's say my lower lobe,
it needs to be removed.

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It's a pretty drastic
thing to have happen,

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but let's say this
is what happens.

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What would change in
terms of my blood flow?

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Well, the thing that
is going to change

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is my resistance
is going to change.

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Let's think about it.

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Before I had this surgery,
I had a certain amount

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of resistance in
this blood vessel

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and also some resistance
in this blood vessel.

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And let's say it's
about the same,

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just to kind of
make things easy.

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Let's say the resistance
was about the same.

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So again, I had a surgery.

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And before they removed the
lower lobe-- just to make sure

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we are clear on what
this surgery was-- so

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removed the lower lobe.

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So before the surgery-- I'll
write "before" up here--

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what was the resistance?

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Well, the resistance I
was facing was-- remember,

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we have a branch here.

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So we have to add up
the total resistance.

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You remember how to do this.

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Total resistance--
I'll call it R total--

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equaled 1 divided by
1 over R-- because we

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said that's what the resistance
is right there-- 1 over R

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plus 1 over R. And that second
one is because of this guy.

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So we just kind of add it up.

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And I would say, OK.

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Well, that's equal to
1 over 2 divided by R.

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And I can flip the
whole thing around.

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And I get R divided by
2 or 1/2 R. So this is

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my total resistance-- 1/2 R.

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It's a little counterintuitive--
the fact that you actually

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have half of the resistance
just because you have a fork.

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The fork in the road--
meaning this fork right

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here-- offers you a chance
to go one of two ways.

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And as a result, the
resistance falls in half.

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So after my surgery,
what was my resistance?

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Well, in my surgery, this
all kind of went away.

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This is now all gone.

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Because my surgery removed the
lower lobes, this is now gone.

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So what is my new R total?

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Well, if I had to
calculate it again,

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I would say, OK, R total.

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In this case, it's
actually really easy

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because it's just
whatever's left.

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In this case, the total
is going to be just R.

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So really, my resistance
went from half R to R.

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And so my resistance really,
by removing the lower lobe,

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it doubled.

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My resistance went much higher.

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So this is the first
interesting point--

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that by having a
half a lobe removed,

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my resistance went way up.

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So on this side, my
resistance after the surgery

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is much higher
than it used to be.

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Now, remember this
flow-- 5 liters a minute.

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Now, you still have that
much blood coming in,

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but now there's extra
resistance on the left side.

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So what's the blood going to do?

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Well, it's going to
say, well, why would I

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go that way when
I can go this way?

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So more of the blood's
going to kind of go this way

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because there's more
resistance on the left side.

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And so I can actually--
I don't know exactly what

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the amount of flow would be--
but I can kind of take a guess.

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And I would say, well, my guess
is that the flow will be lower.

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So I'm actually going
to redo these numbers.

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I'm going to give
you new numbers.

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And let's say the new flows--
I'll write them in green--

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are going to be 3 liters a
minute and 2 liters a minute.

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They still have to add
up to 5, of course.

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That's not changed.

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But you have more blood
going to the right lung.

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So here let me
introduce another word.

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So we've talked
about flow, but now

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let me talk about perfusion.

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And sometimes people actually
think they're the same thing.

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They sometimes will use
them kind of synonymously.

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But really, perfusion
is volume over time.

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And so, so far you're thinking,
well, it is about the same.

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But actually, it's all
divided by amount of tissue.

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And when I say amount,
I could do either

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be talking about a volume of
tissue or a weight of tissue.

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So amount of tissue.

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Just to kind of make this
a little bit more concrete,

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I'm going to assume that I'm
going to use 100 grams here.

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And that's often used.

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Not always.

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Sometimes you'll
see other units.

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But I'm going to
use 100 grams here.

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So let's now think about
this entire scenario

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with the new numbers--
2 liters a minute

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and 3 liters a minute--
in terms of perfusion.

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What would that mean?

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Well, let's say I
weigh out my two lungs.

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And here I only have an upper
lobe on my left side left.

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So let's say that
weighs half a kilogram.

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And let's say, on the right
side, I've got 1 kilogram.

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Let's say this is 1 kilogram.

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These are the weights
of my two sides.

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And to figure out perfusion,
then all you really are doing

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is taking the flow-- because
remember, this whole chunk,

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this whole part right
here is just flow--

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and dividing it by
the amount of tissue.

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So I could figure out
perfusion pretty easily.

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I could say, OK.

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Well, on the right side--
let's do right side first--

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I've got 3 liters a minute.

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I'm going to write that
as 3,000 milliliters,

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just to make it a
little easier to see.

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3,000 milliliters per
minute divided by-- I

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said 1 kilo, which is
the same as 1,000 grams.

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So what does that
turn out to be?

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If I'm going to use 100 grams
as my denominator, I could say,

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well, that's-- let's
see, 0s cancel.

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So I've got 300
milliliters per minute

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per 100 grams of lung tissue.

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And so this is for
the right side.

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And I could do the same
thing for the left side.

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I could say, well, what would
it be for the left side?

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It would be-- I've
got 2,000 milliliters.

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We said 2 liters.

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And of course, the 2 and 3 I
was just kind of estimating.

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But we'd have to
actually measure

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to see what the actual flow is.

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But here I've got 500 grams.

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And so that works out
to 400 milliliters

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per minute per 100 grams.

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So what I wanted to show you
is an interesting thing, which

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is that you can actually
have, on the one side--

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if I said which side,
the right or the left,

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after my surgery, which
side has more blood flow?

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Well, then, this side
has more blood flow.

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The right side has more flow.

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But if I said which
one has more perfusion,

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well, it turns out
that actually that

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left upper lobe is actually
getting more perfusion.

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So just because one
side has more flow

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doesn't necessarily mean
that it has more perfusion.

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Oftentimes that is
the case because you

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can see how closely flow
and perfusion are related.

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But it just depends
on exactly what

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the weight is for the tissue.

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Kind of a classic
example of this

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I'm going to write out over here
that you might hear people talk

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about sometimes is-- if
you say this side is high

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and this side is low-- let's
do flow and perfusion--

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they'll say, well,
if you have flow

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and you're trying to talk
about different organs,

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one of the organs with the
highest flow in the body

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would actually be your liver.

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This is, let's say, your liver.

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This is your liver.

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And then, with a little
bit less blood flow

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would be your kidneys.

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This would be your
kidneys, let's say.

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I'll write K for kidney.

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Or actually, I guess
I'll spell it out.

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I have enough space.

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And then, something
that has almost no flow

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relative to the other
two would be bones.

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And actually, compared
to this, if you

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were to now talk
about perfusion,

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it would actually looks
slightly different.

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So for perfusion-- using
these same three organs--

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if I was to kind of rank
them based on which one gets

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the most perfusion
or blood perfusion,

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the kidney actually
does the best.

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So here you have to take a
certain amount of tissue.

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And it's got to be
the same amount.

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So I'm just imagining if I
took a little chunk of kidney

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tissue.

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And if I did the
exact same thing

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and I took a little
chunk of liver tissue.

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And this is kind
of the way to think

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about it is that, if you
want to balance things out,

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you've got to take the
exact same amount of tissue.

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In this case, it would
be 100 grams, let's say.

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Maybe these boxes are
100 grams of tissue.

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It would be something like this.

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And this would be the bone.

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So the liver ends up
not doing as well.

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It gets a little
bit less perfusion

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in terms of 100 grams.

00:10:13.300 --> 00:10:15.100
The kidney does a
little bit better

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when it comes to perfusion.

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And the bones-- the
sad, little bones--

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they actually don't
get much blood flow.

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And even if you do it
by 100 grams of tissue,

00:10:23.130 --> 00:10:25.609
they actually don't get
much perfusion either.

00:10:25.609 --> 00:10:27.650
So this is kind of another
way to think about it,

00:10:27.650 --> 00:10:29.066
and you might hear
these examples.

00:10:29.066 --> 00:10:31.550
So I wanted to give
them to you here.