Cardiac preload and afterload – what’s the difference?

Recent Quick quiz on our Facebook page resulted in a combination of responses. Do you understand what word is used to explain the quantity of stretch in the center muscle at the top of diastole? The responses were split between cardiac preload and cardiac afterload.

Let’s take a more in-depth have a look at what these terms mean.

Cardiac preload

Preload, also often known as left ventricular end-diastolic pressure (LVEDP), is the quantity of stretch the ventricles get at the top of diastole. Think of it as loading the center for the subsequent big ventricular squeeze during systole. Some people remember it through the use of the analogy of a balloon—blow air right into a balloon and it stretches; the more air you blow, the more stretch.

Cardiac afterload

Afterload, also often known as systemic vascular resistance (SVR), is the quantity of resistance the center has to beat to open the aortic valve and push a volume of blood into the systemic circulation. If you think that of the balloon analogy, afterload is represented by a node at the top of the balloon. In order to get the air out, the balloon has to work against that node.

Cardiac performance and cardiac index

Cardiac output is the amount of blood pumped by the center per minute. Cardiac output is calculated by multiplying the stroke volume by the center rate; normal cardiac output is about 4 to eight L/min, but this varies depending on the body’s metabolic needs. Cardiac index is a calculation of the center’s output divided by the body surface area (BSA) of an individual.

So in case your answer to the above quiz is “D”, you might be correct!

Preload and afterload references:

Hinkle, J., & Cheever, K. (2021). Brunner & Suddarth’s Textbook of Medical-Surgical Nursing, Fifteenth Edition. Philadelphia: Wolters Kluwer.

King, J., and Lowery, D. R. (2023). Cardiac physiology, performance. In StatPearlsStatPearls Publishing House.

Terzulli, D. (2023). Nurse’s guide to hypovolemic shock. (5). https://www.doi.org/10.1097/nme.0000000000000003