Preload and the Frank-Starling Law – Cardiac Mechanics

by Thad Wilson, PhD

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    So, now, let’s get into preload. Preload is very important for the filling component of the heart. That is your left ventricular end-diastolic volume. That's the maximum amount of volume you have in your left ventricle prior to a contraction. Interestingly, when you talk about preload, it’s actually about a fiber length that we’re most concerned about. How much stretch is there on the left ventricle before you contracted again. Those kind of thoughts can be easily seen with things like a balloon. You're filling a balloon until it gets to a certain point or toughness, and that's when you know it's full. But until that point, you have a large space to fill. When looking at preload, there are couple of intrinsic mechanisms associated with the muscle. And here, let's explain those to a greater degree. It depends on how much you fill the heart, how much it's going to be able to contract. The more it's full, the harder it can contract. The less it’s full, the less hard it can contract. So, let’s look at that diagrammatically. When you have a low preload, you don't fill the heart as much. And therefore, at any given left ventricular pressure, you can only push out so much stroke volume. If you fill the heart more at that same level of contractility, you can push out more blood. What factors affect preload? Two of the biggest ones are venous blood volume and venous compliance. So, the more blood volume you have, the more return of blood you have to the heart. If your veins are less compliant, meaning that they are constricted, the more blood you'll be able to return to the heart. That has to do with increasing venous pressure, and specifically, a lot depends on how compliant your...

    About the Lecture

    The lecture Preload and the Frank-Starling Law – Cardiac Mechanics by Thad Wilson, PhD is from the course Cardiac Physiology.

    Included Quiz Questions

    1. Increased atrial inotropy
    2. Increased ventricular inotropy
    3. Decreased afterload
    4. Decreased ventricular compliance

    Author of lecture Preload and the Frank-Starling Law – Cardiac Mechanics

     Thad Wilson, PhD

    Thad Wilson, PhD

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