Compliance – decreased blood pressure | Circulatory system physiology | NCLEX-RN | Khan Academy
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Compliance – decreased blood pressure | Circulatory system physiology | NCLEX-RN | Khan Academy

August 31, 2019


All right, I’m going to
compare two individuals. One individual with very
compliant blood vessels, and that person is going to
be, as a result of the fact that they’re compliant,
they’re going to be very happy. And then one person with
very non-compliant vessels. And that person will be sad. And we also have two
parts of the heart cycle. We have systole and diastole. So we’re going to do it both
for systole and diastole. This is systole, and
we’ll do it for diastole. And I’ll write it
out again, because I want to make sure we see clearly
the difference between someone with compliant blood vessels
and someone with non-compliant. Remember,
non-compliant basically means having stiff
blood vessels. And the processes
that cause this are things like arteriosclerosis
for the large vessels or arteriolosclerosis
for the smaller vessels. And let’s divide it
out with a large line. So let’s imagine that we have
now, for our first person who has compliant blood
vessels in systole. What will that look like? So let’s say you
have your heart here. And I’m going to
stretch out the aorta. So it doesn’t normally
look this way. But I’m just going
to show you what it would look like in a
person that has the ability to have nice, flexible arteries. It would look
something like that. And the same region of the
heart and blood vessels in someone with non-compliant
arteries would look like this. So again, this is right when the
heart is squeezing blood out. So we know that blood
is flowing through here. And in fact, just to
highlight the fact that this person has
very stiff vessels, let me show you kind of these
atherosclerotic plaques sitting inside of their arteries,
making them stiff. So really, they’re
unable to be flexible. They’re not ballooning out. And let me show you what the
vessel kind of would look like, just so you can see how
ballooned out this person’s blood vessels really are here. So this is that inner
dimension of the vessel. This is what would look like
if they didn’t balloon out. But in fact, they did. So let’s take a point,
maybe there and there. And let’s call
that the spot where we’re checking pressure energy. And I’m going to talk
in terms of energy. And this is where we’re actually
detecting pressure energy, let’s say. And this bar represents how
much energy we actually see. So this is a
representation of how much pressure energy is at that spot. And let’s assume
that, even though we know that the vessels are
different in these two people, that their hearts are the same,
that they’re working equally hard, and putting equally
a similar amount of energy into the blood vessels. So we know that the pressure
energy should be quite similar between the two, from
the heart’s standpoint. And we also know that
blood is moving out. So we actually can look at
movement energy as well. And I’m going to draw
that as a bar also. We’ve got movement energy
here in yellow and pressure energy in purple. And as you look at
this, you’re going to see that the
movement energy, I’m going to assume for the
two cases, is similar. So similar-sized bar. And actually, in people
with atherosclerosis, they have compensation,
so these bars actually start looking a
little different. But just for right
now, let’s imagine that we’re just taking
a snapshot the moment after these vessels became hard. So that’s the movement
energy, and I’ll just label it movement. And in purple is
the pressure energy. And what I want you to notice
is that I haven’t addressed a very important point, which
is that this is ballooned out. And so we know that, just like
in a balloon or a rubber band, if you stretch it
out, you’re going to actually start getting
some extra energy. And we call that elastic energy. And that elastic energy
would be something like that. It would actually take up a
chunk of that pressure energy. Because it’s the
pressure in the blood that’s actually causing
the vessels to balloon out. So this is the
elastic energy, which just took a chunk of that
pressure energy away. And what’s left is the
leftover pressure energy. And we have really no
ballooning on this side. So really it’s all
pressure energy. So if I was to actually try
to measure how much energy, and obviously, I don’t
measure movement energy or elastic energy. The only thing I really
measure in the doctor’s office is the pressure energy. And I say, hey, your
pressure was so-and-so. So let’s give some
numbers just so we can keep all this straight. This person might have a
blood pressure, let’s say 160. And the person who’s happy
with compliant vessels might have a blood
pressure of 120. And we can see exactly why,
because some of that energy got taken away and stored
away as elastic energy. So, so far, so good. You can already see how elastic
energy is really helpful, because it helped you
lower the pressure. Now what happens in diastole? So now, the heart is resting. The heart is taking a
quick breather to refill. And the vessels are now a
little bit less full of blood, because a lot of that blood
has already left and gone on to the foot and
the face and all of the different
parts of the body. And this is what the
inside of the vessel looks like again, just to keep
that straight in our heads. And on this non-compliant
person’s vessels, they actually look
basically the same. It’s not going to
look any different. And you’ve got your
atherosclerosis. That didn’t go away. Because this is all
just looking at two different parts
of the heartbeat, the resting and the active
part of the heartbeat. So none of that goes away. And so let’s say I do the
same experiment, where I look at this purple x, and
I take a look at how much pressure energy there is. Now I know there’s going
to be less than before. I know that because the
heart is taking a break. And so this is all
just whatever’s residual, whatever’s
left over from systole. I’ve got a little
bar of purple there. And let’s say that the bar is
about the same height here. And I’ve got some pressure
energy here as well. And already you can see that
the lesson from the first part of this picture was that we have
a little bit of elastic energy here. And you can see that. Otherwise, the two vessels
would look the same. But you can see there are
still some areas where it’s a little stretched out. So let’s draw that in here. A little bit of
elastic energy left. It’s not completely gone. This is my elastic energy. And already, you can see that
that means that, of course, in diastole, my pressure
is going to fall as well. So I’ve got lower
pressures in diastole, just like we did in systole. This is my non-compliant
diastolic blood pressure. And I would even
throw some numbers. I could say this is maybe, let’s
say 100, and up here, maybe 80. Because it’s got to be a
little bit lower, right? Now notice this. This is actually really,
really interesting. Notice this. Notice this elastic energy here. And is it the same
as the amount here? Well, the answer
is obviously no. It’s not the same. There’s less. And so the other cool
feature about elastic energy is not only does it
lower your pressure, which we’ve talked
about, but it also can be used to convert
it into movement energy. So isn’t that interesting? You can actually use this
stored elastic energy– let’s say that’s the difference. I’m just trying to eyeball it. But let’s say this
is the difference. You can actually use
this to move blood. You can actually use
this for movement energy. And so you can see that
this actually adds up. You can see that the
elastic energy before is about the same as
the elastic energy afterwards plus the
movement energy. So there are two
important points here. One is that the elastic energy
helps lower the pressure. We saw that here and here. And two is that
it actually helps you generate movement of blood. And so you can actually,
now in diastole, move some blood forward. And that’s because the
elastic energy is recoiling, just like a rubber band
recoils, and that energy has to go somewhere. And it’s going into
moving some blood forward. So it’s taking a
little bit of blood and saying, OK, move
forward a little bit. And you actually don’t
have that phenomenon, or that interesting, cool
property is not really happening down here. So you don’t have any of that
on the non-compliant side. So these are the things I wanted
to kind of point out to you, and show you why it’s
so important to have flexible arteries.

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  1. You have a real gift to make very complex ideas extremely simple! Thank you for taking the time to share your knowledge.

  2. There is an error in this video. I used a couple of hours trying to figure out why the concepts weren't making sense. A high compliance is associated with a lower systolic blood pressure but a HIGHER diastolic blood pressure. The high compliance means the vessels have a high recoil force that increases the blood pressure in diastole. That is why old people with atherosclerosis have isolated systolic hypertension. This video should have the diastolic blood pressures switched. a non compliant blood vessel would have a lower DBP than a compliant blood vessel. you can think of compliance as a buffer that keeps the pulse pressure (difference between SBP and DBP) low. This also explains why low compliance results in a higher pulse pressure.

  3. There is a huge error in your video.CORRECT IT elasticity is ability to “snap back to the original position after distension and its inverse (reciprocal) of Compliance. In a low compliant vessel blood will flow out of aorta much quicker thus reducing the diastolic blood pressure.

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