Quote from noele1213
Hi there...Is there anyone out there who has had A&P2 and can take a few minutes to explain preload and afterload to me. I have read it too, too many times in many different ways and I'm still not able to invision it (which is what I have to do in order to retain or understand something) So if you can explain with an analogy, all the better> I need a visual...LOL Thanks guys.
First check out this AllNurses.com thread:
I'm not sure about this, but maybe this way will help:
The clearance of the pump - imagine a pump which is basically a hollow rubber ball with tubes coming from it (an inlet and an outlet). If you squeeze the ball slowly the air comes out gradually and without much force, but if you give it a good hard squeeze a lot of air comes out quickly. The same can be done with the heart, the body can increase the amount of blood it pumps out with each squeeze (contraction). The technical term for the amount of blood squeezed out with each contraction is stroke volume (SV). This variable is linked with the stretch of the heart prior to contraction (preload), the force of the contraction (contractility) and the pressure that must be obtained to actually get the blood out of the heart (afterload).
Preload - If the muscle walls of the heart are stretched prior to a stroke then they will squeeze harder on the stroke. To get a greater stretch more blood must be in the heart. This observation is called the 'Frank-Starling law of the heart'.
Contractility - The contractility of the heart is influenced by inotropic agents that make it pump either stronger or weaker. Positive inotropic agents such as Calcium ions and adrenaline make it pump stronger, negative inotropic agents such as potassium ions make the stroke weaker.
Afterload - In order to get blood out the heart the back- pressure in the blood vessels must be overcome. The harder it is to get blood out, the less blood will actually leave the heart. You can imagine if the blood vessels are clogged or narrow that this will make things harder.