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11-16-2015
 Lets_Ace_USMLE USMLE Forums Scout Steps History: 1 + CS Posts: 45 Threads: 23 Thanked 6 Times in 6 Posts Reputation: 16
LV Pressure-Volume Loops

If you want to get every single question on LV pressure-volume loops correct, then follow this.
First we have to start by familiarizing ourselves with terminology. Also, learning different ways of saying the same thing (for example, "increased stroke volume" is the same as saying "increased ejection fraction" and both of these are the same as saying "increased ejection volume").

Let's start by learning the different terms that we need to focus on whenever we are faced with a LV pressure-volume loop ( what I mean here is just learning the names of these terms not explanations, I will provide the explanations later), so the terms:
1- Stroke Volume
2- Ejection Volume
3- Ejection Fraction
4- ESV (End Systolic Volume)
5- ESP (End Systolic Pressure)
6- EDV (End Diastolic Volume)
7- EDP (End Diastolic Pressure)
8- Cardiac Contractility (which can be increased, decreased, or unchanged in pressure-volume loops)
9- Systolic Blood Pressure (which can be increased, decreased, or unchanged in pressure-volume loops)
10-Isovolumetric Contraction (which is represented by a vertical line on pressure-volume loops and can shift in only two directions, either to the right or to the left)
11- Isovolumetric Relaxation (which is represented by a vertical line on pressure-volume loops and can shift in only two directions, either to the right or to the left)
12- Preload (which can be increased, decreased, or unchanged on a pressure-volume loops)
13- Afterload ((which can be increased, decreased, or unchanged on a pressure-volume loops)

OK now that you have survived the different terms used in LV pressure-volume loops, let's group the terms that basically "go together" in terms of "increased", "decreased", or "unchanged": It is a good idea to look at the attached image now to see what I mean by each "line" on the LV Pressure-Volume Loop

1- Stroke Volume = Ejection Volume= Ejection Fraction

2- Isovolumetric Contraction line = EDV line= EDP line = Preload line

( Note that I am not saying these terms are the same, what I am saying is the "line" that represents them on a pressure-volume loop is the same. We use this "line" to determine whether an increase, a decrease, or no change has happened in EDV, EDP, Preload, but for Isovolumetric Contraction we don't care about it because it is not important, but the reason I am mentioning it here is because the line of the Isovolumetric Contraction is a "reference point" that we use to determine if a change has happened in EDV, EDP, and Preload.

3- Isovolumetric Relaxation line = ESV line= ESP line BUT NOT "Afterload line"

( Again notice that I am not saying these terms are the same, what I am saying is the "line" that represents them on a pressure-volume loop is the same. We use this "line" to determine whether an increase, a decrease, or no change has happened in ESV, ESP but for Isovolumetric relaxation itself we don't care about it because it is not important, but the reason I am mentioning it here is because the line of the Isovolumetric Relaxation is a "reference point" that we use to determine if a change has happened in ESV, ESP, BUT NOT "Afterload". Note that in this part I did not talk about "afterload" because "afterload" has nothing to do with the vertical line of Isovolumetric Relaxation.

4- The line to use as a reference point for determining changes in "afterload" is shown on the atached picture.

OK this is the first part of this post. In my next post I will show how to determine if there is a change in "preload", "afterload", "cardiac contractility" and all the things that go with them. Also, if you are doing questions "UWorld, Kaplan, First Aid", use these reference lines and see how much easier you understand when they explain the answer choices.
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