00:01
Now let's go on to our vascular side
of our four parts of blood pressure.
00:05
Remember, we have vascular
resistance and fluid volume status.
00:09
With vascular resistance,
we're measuring the afterload
or the resistance to the blood flow
coming out of the left ventricle.
00:16
This is measured by systemic vascular
resistance on your bedside monitor.
00:20
Normal values is 800-1200 dynes,
when you go towards 800,
that's vasodilating.
00:26
And when you're going higher up to
1200, that's vasoconstriction.
00:31
Now, when you're increasing your
systemic vascular resistance,
so you're going higher
up towards 1200 dynes.
00:37
This will increase your MAP or
it should increase your MAP.
00:41
But also increasing your SVR could
decrease your cardiac output.
00:45
Let's dive into this a little
bit more so we can understand it.
00:50
Now, when you have a
normal size blood vessel,
and you have normal blood
volume going through it,
you're going to have a
normal blood pressure.
00:58
But if we try to increase blood
pressure by vasoconstricting,
we narrow that
blood vessel down,
we have a normal amount of
blood still going through it,
we get a higher blood
pressure at the end of it.
01:10
I call this the
garden hose theory.
01:13
So think of a garden hose.
01:14
When you were a kid, you'd have a
garden hose, you turn the faucet on,
what would you do
to spray everybody?
You would put your
thumb over it.
01:22
Keep that visual in your head.
01:24
Now, let's say that the
garden hose is your aorta.
01:29
The faucet is your heart.
01:31
And the water going through
it is the blood flow.
01:34
Now, when you turn on
the faucet all the way,
and you just have the hose,
you're not putting your
thumb or anything over it.
01:41
What's happening?
You're getting a lot
of blood volume out
but the pressure is
at a moderate amount.
01:47
Now, if you want to increase
that blood pressure,
you want to increase the
pressure of the water,
you put your thumb over it.
01:53
What you're doing is effectively
decreasing that size of that aorta
which is an increasing
the pressure coming up.
02:03
But how much water
is coming out?
Do we have more water,
the same amount of water or less water?
Well, when you're putting your thumb
over it, you actually increased pressure,
but you decrease the
amount of cardiac output,
you decrease the amount
of blood flow coming out.
02:19
That's how systemic vascular
resistance can reduce cardiac output.
02:24
Now your body can overcome this.
02:26
So how does your body
overcome vasoconstriction
so that we get the same
amount of cardiac output?
Well, it has to increase our
heart rate and our contractility
so that we get more cardiac output
to overcome the vasoconstriction.
02:42
Let me show you
this diagram here.
02:44
We have a normal amount of blood
flow coming out of a normal vessel.
02:48
When we vasoconstrict,
we have less blood flow coming out of it.
02:52
So the heart needs to
increase contractility
and increase rate so that
we get more cardiac output
and more blood flow coming
through a smaller vessel.