Frank-Starling Curve and Atrial Dynamics – Cardiac Mechanics

00:01 Let's summarize a number of the changes that happen on the Frank-Starling curve.

00:07 This will allow us to bring concepts together because we know they’re hard.

00:12 But if we review them again, we’ll be able to gain better insight into them.

00:16 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.

00:27 So, let's go through those.

00:29 And increase in preload, you travel along the same curve, but just two upward points.

00:37 A decrease preload, use the same curve again.

00:41 But now, you're going down in the curve, which means you're at a lower left ventricular end-diastolic pressure.

00:50 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.

01:00 That means per amount of left ventricular end-diastolic pressure you’re going to get a greater stroke volume.

01:09 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.

01:18 This means that at any given left ventricular end-diastolic pressure you’re going to have a lower stroke volume.

01:26 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.

01:38 So, let's take a good example that is a fight or flight response.

01:42 This is something where your body is going to have to respond to something and runaway.

01:47 To be able to do that, you're going to have to increase your cardiac output.

01:51 So how are you going to do it? Well, there are a couple of mechanisms that you can start with.

01:56 The first mechanism that you’re going to go through here is you're going to increase the left ventricular end-diastolic volume.

02:06 You're also then going to increase the end-systolic pressure-volume relationship.

02:12 So, both of these effects are going to occur almost at the same time.

02:18 Now the change in left ventricular end-systolic pressure-volume relationship, that is a change in inotropy.

02:25 The change in the increase in left ventricular end-diastolic volume, that is a change in preload.

02:31 So, that is our inotropic change and our preload change.

02:37 Interestingly, what that allows then to happen is for greater stroke volume than would've occurred with either one of them independently.

02:47 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.

02:59 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.

03:07 The top part of the heart also responds to a number of changes in preload, in afterload, in inotropy.

03:16 And these changes will occur and help to facilitate the amount of venous return, or sometimes, we’ll just refer to that as preload.

03:27 If you have an increase in venous return, you will have a greater contraction of the left and right atria.

03:34 That should fill the left ventricles to a greater degree.

03:40 However, 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.

03:56 A lot of stimulation with nerves also affect the atrium's ability to contract.

04:02 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.