Preload and Afterload – What's the Difference?

A recent Quick Quiz on our Facebook page resulted in a mix of responses. Do you know what word is used to describe the amount of stretch on the myocardium at the end of diastole? The responses were split between preload and afterload. 
 
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Let’s take a closer look at what these terms mean.

Preload

Preload, also known as the left ventricular end-diastolic pressure (LVEDP), is the amount of ventricular stretch at the end of diastole. Think of it as the heart loading up for the next big squeeze of the ventricles during systole. Some people remember this by using an analogy of a balloon – blow air into the balloon and it stretches; the more air you blow in, the greater the stretch. 

Afterload

Afterload, also known as the systemic vascular resistance (SVR), is the amount of resistance the heart must overcome to open the aortic valve and push the blood volume out into the systemic circulation. If you think about the balloon analogy, afterload is represented by the knot at the end of the balloon. To get the air out, the balloon must work against that knot. 

Cardiac Output & Cardiac Index

Cardiac output is the volume of blood the heart pumps per minute. Cardiac output is calculated by multiplying the stroke volume by the heart rate; normal cardiac output is about 4 to 8 L/min, but varies depending on the body’s metabolic needs. Cardiac index is a calculation of the cardiac output divided by the person’s body surface area (BSA). 

So, if you answered ‘D’ to the quiz above, you’re right!
References
Gowda, C. (2008). Don't be puzzled by cardiovascular concepts. Nursing Made Incredibly Easy!, 27-30.
Smeltzer, S. B. (2010). Brunner & Suddarth's Textbook of Medical-Surgical Nursing, Twelfth Edition. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.
Warise, L. (2015). Understanding Cardiogenic Shock: A Nursing Approach to Improve Outcomes. Dimensions of Critical Care Nursing, 67-77.
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Posted: 5/26/2015 5:29:45 AM by Lisa Bonsall, MSN, RN, CRNP | with 9 comments


Comments
Arnold Sibanda
Quite informative and good for sharpening critical thinking skills! Will be beneficial for me to follow, as I'm keen on taking the NCLEX-RN this year.
1/6/2017 2:28:59 PM

Anita
This was very helpful, thank you.
10/15/2016 9:14:31 PM

kayse
Thanks. I really like it!
6/24/2016 5:37:45 AM

Paige
Thank you! This helped a lot!
12/1/2015 8:16:24 PM

laxman
it is helpfull for medical students
11/24/2015 11:35:33 PM

Lisa Bonsall, MSN, RN, CRNP
Hi Krishna ~ you can become a member of NursingCenter by registering here: http://www.nursingcenter.com/LoginRegister
Thanks!
Lisa
11/20/2015 12:37:31 PM

Krishna gopal
Me a nurse in a conmunity as a community nurse. Plz subscribe me
11/20/2015 2:59:21 AM

Shahzad Ahmed Malik
its really helpfull
10/26/2015 10:10:32 AM

Evonne Smith
Thank you, I like these quizzes to help me remember facts.
6/15/2015 7:13:11 AM

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