cfaulknor Posted March 12, 2007 Share Posted March 12, 2007 Hello Again... I am going through Paramedic Class, and I just can not grasp the concept of Preload and Afterload and that general idea... could anyone put it into some simpler terms for me? Thanks Link to comment Share on other sites More sharing options...
Just Plain Ruff Posted March 12, 2007 Share Posted March 12, 2007 Try here. Pretty good info. http://www.answers.com/topic/preload-cardiology Link to comment Share on other sites More sharing options...
SnowFlight Posted March 12, 2007 Share Posted March 12, 2007 In easy to undertand terms: Preload = Volume (End Diastolic Vol.) Afterload = Pressure & Resistance (Art. Pressure & Vascular resistance) Putting it all ito context is where it becomes a bit more difficult. Toget you headed in the right direction on how these two terms interact and affect caridac physiology I would reccomend you take a look for these terms as well: Contractility & Frank – Starling Principle Cardiac Output & Stroke Vol. Vascular resistance hope this helps Link to comment Share on other sites More sharing options...
chbare Posted March 12, 2007 Share Posted March 12, 2007 Chris, what about these concepts are you having difficulty understanding? Is it simply confusing the two, or is the entire concept foreign? Preload is basically the amount of pressure in the left ventricle following atrial contraction. Hence the term "atrial kick." Preload is related to two mechanisms. 1; the pressure and venous return from the body and 2; a properly functioning right ventricle. Since preload is dependant upon venous return, conditions that cause low venous pressure will reduce preload. (hypovolemia and loss of venous tone) Preload is an important part of cardiac output, because the stretch of the ventricle caused by preload helps to increase the pumping action and total amount of blood pumped by the left ventricle. This is often called "Starlings Law of the Heart." Afterload is basically the amount of pressure the left ventricle must overcome to open the aortic valve and pump blood to the body. In the absence of all other factors, increased afterload will cause decreased cardiac output. So, to keep from confusing the two, you can look at preload as being related to the venous system and afterload as being related to the arterial system. A very basic generalization; however, it may help to differentiate between these two concepts. I hope this helps. Take care, chbare. Link to comment Share on other sites More sharing options...
AZCEP Posted March 12, 2007 Share Posted March 12, 2007 I think my colleague from New Mexico made an error. Preload is the amount of volume/pressure that is present following Ventricular contraction, not atrial. Afterload is the amount of pressure that the ventricles must contract against. Excellent description of why it's important. Link to comment Share on other sites More sharing options...
kevkei Posted March 13, 2007 Share Posted March 13, 2007 I think my colleague from New Mexico made an error. Preload is the amount of volume/pressure that is present following Ventricular contraction, not atrial. With the utmost respect, I would agree with AZCEP. Preload is what causes the right atrium to fill (without it, it wouldn't) The higher the preload, the greater the filling of the atrium due to stretch (Starlings law) and the greater the atrial kick you subsequently get to the ventricle. Link to comment Share on other sites More sharing options...
chbare Posted March 13, 2007 Share Posted March 13, 2007 Actually preload can apply to both the ventricle and atrium. We most often associate preload with the left ventricle; however, the technical definition of preload is the sarcomere stretch just prior to a heart chamber contraction. It seems there are a few different schools of thought regarding preload. The following link explains my point of view and education regarding preload. http://www.cvphysiology.com/Cardiac%20Function/CF007.htm Take care, chbare. Link to comment Share on other sites More sharing options...
AZCEP Posted March 13, 2007 Share Posted March 13, 2007 I'll admit that I was locked into the ventricular aspect of the term. Considering diastole is applicable to atria and ventricles, the use of the end-diastolic volume/pressure tends to muddy things a bit. Compounding the problem is the attempt to apply fixed definitions to a structure that moves between phases so quickly. Isn't cardiology fun?! Link to comment Share on other sites More sharing options...
chbare Posted March 13, 2007 Share Posted March 13, 2007 AZCEP, I agree. After thinking about this for a while, I can see how somebody can easily get confused even with the basic concepts of hemodynamics. Take care, chbare. Link to comment Share on other sites More sharing options...
kevkei Posted March 13, 2007 Share Posted March 13, 2007 AZCEP, I agree. After thinking about this for a while, I can see how somebody can easily get confused even with the basic concepts of hemodynamics. Take care, chbare. Isn't that half the problem (fun)? Understanding concepts? From a student Paramedic perspective, isn't the concept they need to understand first in order to apply the complex physiology? The simplest concept to understand in my view is preload is the pressure coming into the heart and afterload is the pressure exiting through the atria. The simple concept, once understood helps create a more clear picture to the individual (all of us), right? To take chbare's description, it is accurate. It would also be fair to say that preload is relative to each chamber of the heart with respect to the pressure exerted upon it from the location the blood is coming from. In essence, preload is not constant through each respective chamber. Consider RVH (right ventricular hypertrophe), it's preload might be within normal limits but due to increased afterload (realative) through the pulmonary vasculature in PPHN, it enlarges due to workload. It also commonly results in cor pulmonale, but again, it is afterload that is the issue. We could talk about PCWP's and such, but that I think that is semantics, it is the concept we are trying to portray. Put yourself in cfaulknor's position, what are they trying to understand? What does RVH matter to them if they have no idea of the concept of pre/after load? Link to comment Share on other sites More sharing options...
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