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Preload and Afterload

9 videos
After using your jeans for a while, you’ll begin to notice small tears and rips developing in the fabric. Why doesn’t this happen to your heart as well? Well, your heart manages to stay healthy despite all of the “wall stress” that pulls on the heart walls. During different parts of the heart cycle (afterload vs. preload) the mechanics of “wall stress” change dramatically. Learn exactly what preload and afterload mean, and how we can use pressure-volume loops to estimate their values.

Why doesn't the heart rip?

VIDEO 10:26 minutes
Understand LaPlace's law to see the effect that pressure, radius, and wall thickness each have on the "wall stress" in the left ventricle. Rishi is a pediatric infectious disease physician and works at Khan Academy.

What is preload?

VIDEO 13:33 minutes
Some say Preload = End-Diastolic Pressure, others say Preload = End-Diastolic Volume, so which one is it? Watch and find out! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Preload and pressure

VIDEO 12:23 minutes
Find out how left ventricular end-diastolic pressure helps you make an educated guess about preload. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Preload stretches out the heart cells

VIDEO 12:41 minutes
Find out why stretching a heart cell in diastole affects how forcefully it contracts in systole. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Frank-Starling mechanism

VIDEO 14:18 minutes
Carefully follow 5 different preload scenarios to see how each one will have a different effect on how actin and myosin line up. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Sarcomere length-tension relationship

VIDEO 8:50 minutes
Find out why the length of a sarcomere (in diastole) affects the amount of force that it can generate (in systole), and how that would look on a graph. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Active contraction vs. passive recoil

VIDEO 7:31 minutes
Go through the similarities and differences between the sarcomere and a slingshot! Rishi is a pediatric infectious disease physician and works at Khan Academy.

What is afterload?

VIDEO 10:28 minutes
Rishi is a pediatric infectious disease physician and works at Khan Academy.

Increasing the heart's force of contraction

VIDEO 14:30 minutes
Find out exactly how stretch increases force of contraction in end-diastole, whereas more calcium increased force of contraction in end-systole. Rishi is a pediatric infectious disease physician and works at Khan Academy.