Preload, Afterload, Contractility

EricJRN, MSN, RN · Jun 24, 2006

Might be outside the scope, but if you teach them about assolute and relative refractory periods on EKG's, make sure you give them the toilet analogy. (Refractory periods are a lot like commodes. When you flush a commode, for a moment there's an absolute refractory period where no other flush can occur. Then a little bit later, you come to a relative refractory period where a flush will happen, but it won't be a normal, strong flush by any means. Works the same way in the heart.)

Not sure what the makeup of your class is like, but in my EMS training that analogy really worked with a class full of paramedic students.

KristiePDX · Jun 24, 2006

I agree, that is a good analogy. If teachers/staff would have used that analogy, it would have cleared up a half an hour of questions during class. Thanks!

PANurseRN1 · Jun 24, 2006

Might be outside the scope, but if you teach them about assolute and relative refractory periods on EKG's, make sure you give them the toilet analogy. (Refractory periods are a lot like commodes. When you flush a commode, for a moment there's an absolute refractory period where no other flush can occur. Then a little bit later, you come to a relative refractory period where a flush will happen, but it won't be a normal, strong flush by any means. Works the same way in the heart.)
Not sure what the makeup of your class is like, but in my EMS training that analogy really worked with a class full of paramedic students.

This made me LOL, but it is an excellent analogy!

Beary-nice · Jun 24, 2006

I like the explanation given for preload, afterload and contractility that is given in the book...Critical Care Nursing Made Incredibly Easy. It uses a balloon analogy where you have to think of the heart as a balloon. Preload is the balloon stretching as air is put into it...the more air...the more stretch...you know the Frank-Starling thing...Contractility would then be similiar to the more air you put in the balloon the more stretch...the further it will fly...it's the inherent ability it has...and afterload...would be like a knot tied in the end of the balloon or the pressure that the air must work against to get out.

I like to use this explanation when tutoring in patho and physio because it can be hard to grasp...it even took me awhile. You could even use a balloon and demonstrate...which I'm sure they would get a bang out of or make one of them come up and demonstrate... :devil: ...that would be fun too.

Good luck...I like instructors who want to make learning fun! And it's important for nurses to grasp this info...it means a lot with disease processes and meds (why the are given...to decrease afterload...etc).

VickyRN, MSN, DNP, RN · Jun 24, 2006

Might be outside the scope, but if you teach them about assolute and relative refractory periods on EKG's, make sure you give them the toilet analogy. (Refractory periods are a lot like commodes. When you flush a commode, for a moment there's an absolute refractory period where no other flush can occur. Then a little bit later, you come to a relative refractory period where a flush will happen, but it won't be a normal, strong flush by any means. Works the same way in the heart.)
Not sure what the makeup of your class is like, but in my EMS training that analogy really worked with a class full of paramedic students.

LOL! Great analogy!

VickyRN, MSN, DNP, RN · Jun 24, 2006

I like the explanation given for preload, afterload and contractility that is given in the book...Critical Care Nursing Made Incredibly Easy. It uses a balloon analogy where you have to think of the heart as a balloon. Preload is the balloon stretching as air is put into it...the more air...the more stretch...you know the Frank-Starling thing...Contractility would then be similiar to the more air you put in the balloon the more stretch...the further it will fly...it's the inherent ability it has...and afterload...would be like a knot tied in the end of the balloon or the pressure that the air must work against to get out.
I like to use this explanation when tutoring in patho and physio because it can be hard to grasp...it even took me awhile. You could even use a balloon and demonstrate...which I'm sure they would get a bang out of or make one of them come up and demonstrate... ...that would be fun too.
Good luck...I like instructors who want to make learning fun! And it's important for nurses to grasp this info...it means a lot with disease processes and meds (why the are given...to decrease afterload...etc).

I really like this illustration. Think I'll try this in class. Thank you so much :)

nedanurse · Jul 13, 2006

hello nurses, I am so proud to be amoung you . I have been a nurse for 1year and am so glad I did it. The only thing I hate baout it is the way we treat eachother. I love my patient population. Very sick people and I help them get better. I dont know if I am at the right place to do it. How to getr along with out getting walked on???

SEOBowhntr · Jul 28, 2006

I agree, the balloon thing is an excellent analogy. I don't think there is a much better one.:cheers:

augigi, CNS · Aug 2, 2006

I teach VADs to doctors, surgeons and nurses (crit care and floor nurses) as well as to patients and carers (sometime 80yo's!).

The best way I have found to describe cardiac preload and afterload is a garden hose...! To get more out of the hose, you can squish it (more afterload, vasopressors) or you can turn the tap up (more preload, makes the hose stretch, get more out). If you kink it off (too hypertensive), it tries under higher pressure and the hose can break, but less comes out. If the hose sits in the sun and dilates, more comes out at lower pressure.

For contractility, a rubber band - with a new one, the harder you pull it, the further it flies when you let go, just like a good, normal heart. With an old, flaky rubber band, you have to pull harder to get a decent flick out of it (need more volume to get a good output) - because the elastic fibres are gone. this also explains dilated cardiomyopathy.