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Afterload and Preload Concepts

Preload is the ventricular stretch at end-diastole; Afterload is the resistance the ventricle must overcome during ejection. They are primary determinants of cardiac work.

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The statement of the theorem

Let

P_{LVEDP}

be the Left Ventricular End-Diastolic Pressure and

P_{Aorta}

be the mean aortic pressure. Preload is defined by

P_{LVEDP}

and

EDV

. Afterload is defined by the systemic vascular resistance

R_{sys}

and the mean aortic pressure:

Afterload \approx R_{sys} \cdot P_{Aorta}