Hypertension effects on the heart | Health & Medicine | Khan Academy

Hypertension effects on the heart | Health & Medicine | Khan Academy


So we were talking in a previous
video about hypertension and the damage that
it causes on the body. And what I’d like to do is
pick up where we left off and finish that conversation. And we had kind
of divided things up into receiving
high blood pressures and generating high
blood pressures. And receiving high pressure–
really, that means the vessels, right? That’s where the pressure
is going to be seen. And so the vessels
can get damaged. And we talked about some
of the different ways that that can happen. And in fact, there are the
larger arteries and also the smaller arteries. But now, let’s
focus our attention on generating high pressures. Because this might be less
intuitive, but actually making the pressure go so high
is not an easy thing to do. And it’s actually a
very challenging task for the heart to accomplish. And in trying to figure it
out, sometimes the heart can run into troubles. So there was an equation,
and that equation was delta P equals
Q times R. And I thought we had put some
words to this equation. So the idea that delta
P– that’s basically saying the arterial pressure
minus the venous pressure. So if you have blood
and it’s exiting here, and that’s got a
certain pressure on it. And as it enters again on the
other side into the atrium, it’s got a pressure
on the venous side. So we’re saying that
the pressure leaving in the arteries minus the
pressure returning in the veins is what’s going to help you
take a certain flow of blood, Q, past the resistance
in the vessels. So that’s a way of
thinking about it. And specifically–
let me actually draw out some of
this resistance. You have, of course, resistance
once it gets into the arteries. And so you’ve got some,
R, resistance there. Then you’ve got more
resistance once you get into the arterioles. In fact, I’m going to
triple underline that one because there’s lots of
resistance in the arterioles. And then you’ve got
resistance in the capillaries, and you’ve got
resistance in the veins. And then you’ve got the blood
returning into the venous side. So there’s resistance in
the circulatory system. And there’s a flow of
blood that you’re actually trying to move around, right? So anything, anything at all,
that increases the resistance or increases the flow is going
to force the amount of pressure you have to put in on the
arterial side to go up. And now if I draw it out,
you’ll see even more clearly why this is a problem. So if you have, let’s
say, the left ventricle, and I’ll leave a little
space for the valves. And this is the
chamber of the heart that’s doing the pumping now. And it’s pumping the
blood out into the aorta. This is the aorta. And this is another valve. And this valve is called the
aortic valve– pretty easy to remember name, aortic valve. And it separates the aorta
from the left ventricle– LV for Left Ventricle. So the left ventricle
is basically going to have to try to get
blood through this door, through this valve. And the way to do that is to
apply a force to that blood and force it through that door. Now, the aortic valve
has a certain area. And so if you remember, any time
you have a force over an area– I’ll write that
over here– anytime you have a force over an
area, you have a pressure. And in this case, that
is the arterial pressure. So when I talk about
arterial pressure, I’m actually talking
about the force that the left
ventricle generates on that aortic valve,
that area of aortic valve. So now, think about it. If you have, let’s
say, more resistance. Let’s say there’s lots and lots
of resistance in the vessels, so that all these numbers
are slowly going up, up, up. Well, that’s going to cause the
overall resistance to go up, and now the left ventricle
has to put more force. Or you could say, what
if you have larger flow? You actually have a
larger volume of blood you’re trying to move around. Again, the aortic pressure
is going to have to go up. So the way that the left
ventricle accomplishes this or tries to accomplish
this is by basically building more muscle. So this is one strategy. It’ll say, OK, well, if I
need to generate more force, why not generate more muscle? So this becomes very
muscular in here. If you actually
look at a heart that has had high pressures
over the years, oftentimes you have what’s
called left ventricular hypertrophy. So on the surface, this
sounds great, right? Left ventricular
hypertrophy sounds like you’re making the
muscle of the heart stronger. And that sounds
like a good thing. You know, that’s certainly
why I go to the gym. I want my muscles to get bigger. So it’s confusing, then, to hear
that that’s not a good thing, and here’s why. So now, imagine you
have all this muscle, and you’re feeling really good. But then I tell you
that, well, this muscle’s using more oxygen. So it’s using more oxygen. But you notice I didn’t draw
any new blood vessels yet. So there are no new blood
vessels getting oxygen to this muscle. But the muscle is definitely
using a lot of energy, and it needs a lot of oxygen. And so what happens
is that you have areas where blood is
basically able to get to those areas and
other areas where blood is not able to get there. And where the blood is unable to
get enough oxygen to that heart muscle, you could
have a heart attack or a myocardial infarction. So left ventricular
hypertrophy is a way of compensating
for needing more force. But it comes with a
little bit of a risk because now you might have a
risk of an MI or Myocardial Infarction. The other possibility is
that the left heart doesn’t compensate, and you have what’s
called left heart failure. And what that basically means
is that the left heart says, you know what, I can’t generate
the pressures that are being required to move all that
blood around, and so I won’t. I won’t generate
those pressures. I’ll do the best I can, and
maybe I can’t move, let’s say, six liters of blood around the
body, but I can do 5 liters or 5 and 1/2 liters. So it’ll try to do what it
can to move as much blood as possible, but it is essentially
not compensating completely. And that’s why you sometimes
see people with heart failure after having years and years
of high blood pressure. Their heart simply
can’t keep up. And so you experience
heart failure.