So now we know the four
parts of blood pressure,
and we know how to look and find out
the four parts of blood pressure,
how to measure them.
Now let's look at what they mean and
how they affect the blood pressure.
the first is the heart rate.
Remember, our normal range is
about 60-100 beats a minute.
When your ventricle
start to beat faster,
meaning your heart
rate goes up faster,
then your blood pressure will start
to increase up to a certain point.
Once it reaches a certain point,
then your ventricles
do not fill adequately.
And you lose that Frank Starling
law means you lose that stretch.
So a fast heart rate affects
blood pressure by two ways.
It doesn't allow the ventricle to fill
up enough with enough blood volume.
And it decreases contractility because you
lose that Frank-Starling law that stretch.
Now, if your heart
rate is too slow,
basically, you don't have
enough cardiac output,
because you're not getting
enough blood out per minute,
because the heart
rate is too slow.
That's going to be under 60.
Now, what determines how it's
too fast and how it's too slow
and when you have
low blood pressure?
It's really patient dependent.
You may have a patient
that has a blood,
a heart rate of 130 beats a minute,
and their blood pressure may be fine.
Or then you have another patient that
their heart rate is 160 beats per minute,
and their blood pressure is
really, really low.
Or vice versa, you may have
a patient that's bradycardic
and have a heart rate of 35
and they are still
maintaining a decent MAP.
The next patient, you come in that
bradycardic might be a heart rate of 45
and they are symptomatic and they've got
a blood pressure or a MAP that's under 60.
So it's really patient dependent
when it comes to heart rate.
The second part of your heart that affects
blood pressure is the contractility.
We know how to look at
We can visualize our contractility
with an echocardiogram.
But if you don't have a
or you're not able to get one,
then we can look at it secondarily
by our cardiac output/index.
I want you to remember though, if you
have a low cardiac output and index,
it doesn't automatically mean
your contractility is too low,
because there's so many
determinants in it.
The determinants of cardiac
output are heart rate,
preload, and afterload.
So basically, you need to rule out all
the three other parts of cardiac output
"My contractility is the issue."
So you're the first to
look at heart rate and say,
my heart rate is within normal."
and my EKG is normal,
then you go to preload and go, "My tank
is full, I've got enough fluid volume."
Then you look at your afterload with
your systemic vascular resistance and,
"Hey, I'm between 800 and 1200,
that's not affecting my cardiac output."
So then you can say,
"It's probably my contractility.
I may need an echocardiogram
or start a medication
that can increase
So cardiac output,
just reviewing remember it's 4-8 L/min.
as a heart rate increases,
and contractility increases,
so does our cardiac output.
But the heart rate can be too fast
where the ventricles don't fill
and we don't get
that that stretch,
which would cause a
decrease in cardiac output.
I want you to look at the picture and
see as that left ventricle stretches,
and then contracts, that's a
visualization of our cardiac output.