Inotropy: Definition, Regulation and Effects – Cardiac Mechanics

by Thad Wilson, PhD

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    Inotropy. Inotropy is going to be the force at which a contraction occurs. This is a length independent activation, meaning that it doesn't matter how much stretch the cardiac myocyte is under. It’s how much force it's going to be able to contract. In this case, it depends upon the preload, but it is independent of preload in many ways. The stroke volume will increase, as you increase the force of contraction or inotropy. So, what are the big factors that affect inotropy? There are four. The first of which is sympathetic activation. The more of a fight or flight response you have, the greater the contraction of each individual heartbeat. You notice, or remember from previous lectures, that you also increase the beat frequency. But in this case, you increase the strength of the contraction. Circulating catecholamines is the second reason. And again, a catecholamine is a blood-borne either epinephrine or norepinephrine. It’s usually produced from the adrenal medulla and that will be traveling around to the circulation, bind to the beta-1 adrenergic receptors to increase ventricular inotropy. The other two factors: One is an increase in heart rate. And this is something called a Bowditch effect. These particular effects, as the heart beats more and more frequently, it gets a little bit stronger in its contraction. And this process, we’ll get into a little bit more with skeletal muscle, but in this case, know that the principle is the same. The last thing that affects inotropy is going to be the afterload. You have to overcome a certain afterload to be able to push out a particular amount of blood. And if afterload increases, inotropy will increase to overcome that afterload because, remember, you have these interrelated effects. So, let’s look at – I mean, inotropy affects ventricular...

    About the Lecture

    The lecture Inotropy: Definition, Regulation and Effects – Cardiac Mechanics by Thad Wilson, PhD is from the course Cardiac Physiology.

    Included Quiz Questions

    1. Decreases stroke volume
    2. Increases stroke volume
    3. Does not change stroke volume

    Author of lecture Inotropy: Definition, Regulation and Effects – Cardiac Mechanics

     Thad Wilson, PhD

    Thad Wilson, PhD

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