Cardiac Preload and Afterload

Think of it like a garden hose.

Preload is about volume. If the watre pressure is low, the water output will be a trickle, not enough to water and sustain your pretty garden.

If the volume is too much, it will back up your plumbing system (Right-sided heart failure engorged liver, systemic edema, etc, or left-sided faiolure pulmonary edema.)

Afterload is about pressure or resistance. If there is a link or narrowing in your garden hose, the volume will back up AND the output will drop.

I can't really make a good analogy about the hose and low afterload, just less resistance, may end up w a relative hypovolemia ie use water glass and med cup analogy.

Fill a med cup (30cc) with water. Med cup is your normal vascular system, filled w normal blood volume. Pt becomes septic, results in massive vasodilation, which is like taking that 30cc of water, and pouring it into an 8-oz glass, it is a relative hypolvolemia, so most blood volume will be shunted to major organs, and periphery and kidneys will be sacrificed.

Just think in this way Preload = Volume
Afterload = Pressure/Resistance

iam new here LPN to RN program very helpful explaination. thanks

1. Pre-load is the filling pressure of the heart, the pressure the heart has when it is relaxing. (Volume- In)

2. After-load is the pressure of the contracting heart. (Resistance-push- Out)

preload=volume/stretch measured in CVP/PCWP
afterload=resistance measured in SVR

Gross analogy, but works for me....

Thing about flushing a toilet......
you flush, and then flush again right away......nothing happens right? THis is because the tank doesn't have time to fill....PRELOAD is decreased in the tank.

What if the toilet is plugged up? When you flush, it backs up....this is too much afterload.

Hi,

I am a student nurse and I need help from a professional
I want to know why hypertension or high blood pressure is common in patient with diabetes mellitus how is this happen?

thanks!

funny thing, i am taking my cardiac classes right now. i asked the professor about preload and afterload today and she simply replied that i need to read the material over again. i do hate it when they won’t take a minute or two to explain anything and very glad that most of our professors are not like that.

i just want to see if i understand preload and afterload now that i have read the replies to the question. is it that preload is the blood in the heart and the pressure caused by this and the afterload is the blood in the arteries when it leaves the heart and the pressure exerted by such?
i am very interested in the heart and wish our cardiac professor knew more about it and was more interested in answering our questions. she has admitted not understanding much of the content in the powerpoints she has posted. there is much she simply does not cover and tells us we will have to learn it on our own. we shall see what happens.
i’m so glad someone else had posted about this. i have yet to figure out how to post on this site. i joined, got the confirmation e-mail but every time i click on the link, internet explorer closes. i finally gave up.
hikingcole

in student terms:

preload = pressure inside the heart during diastole (resting phase)
-starling curve. to a point, the more volume sitting in a chamber, the better a heart works

afterload = pressure the heart has to overcome to squirt blood out of the ventricle
-anything that causes resistance. from a malfunctioning valve to tight arteries to standing on your head.