Let's summarize a number of the changes
that happen on the Frank-Starling curve.
This will allow us to bring concepts together
because we know they’re hard.
But if we review them again,
we’ll be able to gain better insight into them.
And as you see them change in close proximity,
you’ll be able to comprehend
all the different changes that happen
because, remember, nothing ever changes in isolation.
So, let's go through those.
And increase in preload,
you travel along the same curve,
but just two upward points.
A decrease preload, use the same curve again.
But now, you're going down in the curve,
which means you're at a lower
left ventricular end-diastolic pressure.
If you have an increase in inotropy
or a decrease in afterload,
you shift the whole curve to the left
and upwards a little bit.
per amount of left ventricular end-diastolic pressure
you’re going to get a greater stroke volume.
If you have an increase in afterload
or a decrease in inotropy
you get a shift in which the curve moves downward
and to the right.
This means that
at any given left ventricular end-diastolic pressure
you’re going to have a lower stroke volume.
Now, let's really dive in to these interrelationships
because there are certain times that
the body is going to change multiple things
at the same time.
So, let's take a good example
that is a fight or flight response.
This is something where your body is going
to have to respond to something and runaway.
To be able to do that,
you're going to have to
increase your cardiac output.
So how are you going to do it?
Well, there are a couple of mechanisms
that you can start with.
The first mechanism that
you’re going to go through here
is you're going to increase
the left ventricular end-diastolic volume.
You're also then going to increase
the end-systolic pressure-volume relationship.
So, both of these effects are going to
occur almost at the same time.
Now the change in left ventricular
end-systolic pressure-volume relationship,
that is a change in inotropy.
The change in the increase
in left ventricular end-diastolic volume,
that is a change in preload.
So, that is our inotropic change
and our preload change.
what that allows then to happen
is for greater stroke volume
than would've occurred with either one of them independently.
So, this sympathetic stimulation utilizes multiple mechanisms
/to make that curve as wide as possible
and that wide curve gives you a bigger stroke volume.
If you have a large stroke volume,
then all you need to do is beat more frequently
and you’ll have a higher cardiac output.
The top part of the heart
also responds to a number of changes in preload,
And these changes will occur
and help to facilitate the amount of venous return,
or sometimes, we’ll just refer to that as preload.
If you have an increase in venous return,
you will have a greater contraction
of the left and right atria.
That should fill the left ventricles to a greater degree.
if you have too much flow in those areas,
you can lead to things like
regurgitation of the valve;
and sometimes if there are stenotic valves,
you can also get some buildup
of fluid within the ventricles.
A lot of stimulation with nerves
also affect the atrium's ability to contract.
There, a sympathetic nervous stimulation
will give an increase force of contraction,
and vagal stimulation typically allows
for greater amount of failing to occur,
but does not change ionotropy.