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Preload vs. Afterload

Discussion in 'Step I' started by DRealDrZ, May 30, 2004.

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  1. DRealDrZ

    DRealDrZ Senior Member

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    OK, I suck...
    I must be a moron because I seem to get these two things wrong all the time. I think I understand them and then I can't get any questions right about these subjects. Can someone please, please, please, PLEASE explain this very simple concept to this PEABRAINED student? :confused:
  2. babinski bob

    babinski bob Senior Member

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    To keep it simple...

    AFterload = the pressure the heart pumps against... Essentially, it's equal to aortic pressure... Therefore, in HTN, the afterload is increased! Or in aortic stenosis, the afterload is increased!

    Preload = ventricular filling. Thus, the more you fill the ventricles the greater the preloading! Venoconstriction, for example, preloads the heart.

    I think if you keep these examples in fine, you'll be fine.
  3. BrooklynDO

    BrooklynDO Senior Member

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    i also have a pea brain so this is how i think of it

    as soon as i see those words i picture an aortic valve, and everything in front of it is the arterial stuff and everything behind is lungs and viens
    so PREload is whats behind the aortic valve... all that stuff that just came from the lungs , its about to go through the aortic valve hence pre
    and afterload, is all the bs the ventricle has to pump against (all the blood in front of it, or "behind" the aortic valve)

    this makes a lot less sense once I write it, but it works for me
    :luck:
  4. DRealDrZ

    DRealDrZ Senior Member

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    Thanks alot for the help
  5. applehead

    applehead New Member

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    Hey - I also don't get this very well

    I (think I) understand preload and afterload but have a couple of questions.

    I know aortic regurg causes increased afterload due to increased systolic BP, but i don't understand why. I always thought the BP would drop, as less blood is being pumped into the aorta (as more blood leaks back into the LV)

    Also why does a mitral regurg cause a decrease in afterload?

    Any simple explanations would be great!
  6. GOGETA

    GOGETA SuperSaiyan

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    Also why does a mitral regurg cause a decrease in afterload?

    Afterload is what goes into the aorta and will give you pressure so when you pump the next time you also have to move that blood too.

    So you try to pump blood but part of it goes back to the atria, not cool so now the amount of blood that actually whent to the Aorta is LESS, now when you try to pump the blood away from the heart you have LESS pressure to handle. and thats why in a mitral reg. you have a decrease afterload.

    I hope I'm right but if not, please correct me.
  7. GOGETA

    GOGETA SuperSaiyan

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    Because the ventricle has more blood in it, will have to contract harder. wait this theory would explain an increase in preload not afterload:confused:

    Dough
  8. UCLAstudent

    UCLAstudent I'm a luck dragon!

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