Pre-load question from nursing student

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Hi everyone,

I'm a nursing student and I just had an exam last week where a question on the exam asked about factors that might increase pre-load.

One of the answers was tricuspid stenosis, so I did NOT pick that one, b/c I understand pre-load to be the volume in the ventricles at end-diastole, nothing to do with the volume in the atria. Therefore, if there is tricuspid stenosis, LESS volume would be getting to the right ventricle, thus less pre-load.

However, she picked it as a correct answer (it was a select-all-that-apply type question). I got all of the answers on that question right, except for that one.

Can you take a look at the below e-mails and tell me if I'm completely off base? Am I right or wrong? I just sent the most recent e-mail and am waiting for a reply. Today is Sunday night and we have class Tuesday night, so not sure if I'll get a reply before then or if she'll just talk to me in class. I'll post the e-mails in order:

Hi Dr. XXXXX,

I just wanted to follow up with you on one of the questions from the exam last night that you went over in class afterward.

For the question regarding which factors would elevate preload, you had tricuspid stenosis as one of the correct answers.

I didn't put that as one of the answers because I though that preload was only in reference to the ventricles, not the atria.

Therefore, my thought process was that the tricuspid stenosis would decrease the amount of venous return getting back to the right ventricle, thus decreasing preload, not increasing it.

Slides 12-17 in the powerpoint "Concepts of Cardiac Output" seem to mention only the ventricles in relation to preload and not the atria and the textbook on page 218 states "Preload, then, is the volume of blood in the left ventricle at the end of diastole." Page 255 states "Preload is the volume in the ventricle at end-diastole."

I know we are only supposed to use the textbook as a reference, but a few other websites I looked at also seem to only mention the ventricles.

Am I looking at this the wrong way? I hope this doesn't come off the wrong way, I'm just confused and want to make sure I have this correct in my mind.

Thanks in advance for your time.

Sincerely,

XXXXX

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Dear XXXXX,

I explained this principle in class. Just step back and think about this.

Blood moving through the heart. Blood moves through both the atria and the ventricles. So while we emphasize the ventricles because that is what cause the bigger pump or push forward it is also important to think of the atria because if the atria don't fill

the ventricles the ventricles have nothing to pump. The heart has to work as one, with both pieces working together. Don't take things so literal. I can see you are a literal thinker or like things black and white. The body is abstract and you need to look

at the broader picture.

Think of this analogy. If you are walking through double doors. The 2nd door (the

ventricle is working) but the 1st door you can't really get through because the

door only opens part way. Then only 2 people will get through vs 6. Those people that don't get through will cause a back up (in the atria) this will increase people volume as in the heart would increase blood volume. It still increases volume or preload.

The heart must be looked at as one. Not in isolation. This is why I draw the picture on the board. Plus where does the CVP to measure preload sit? Prior to the R atria. So the way it will sense increased volume or preload is if it increases in the atria right?

I hope this helps in clarification.

Dr. XXXXX

Hi Dr. XXXXX,

Thanks for getting back to me. My issue isn't that I don't understand the concept or that I'm not able to think abstractly or in a broader sense, my issue is the definition of pre-load by the textbook vs the definition you are using for the exam, because the definition used changes the answer to the exam question.

If we go by the textbook (and we as students have been told to go by the text for as long as we've been in the program), preload is the volume in the ventricles at end-diastole (page 255). Though I understand that the pressure in the atria (or just above it, as with CVP) is a good indicator of preload, from what I can tell from the textbook and other various sources, it is not the actual definition of preload itself, which seems to only refer to the ventricles.

I really have made a good-faith effort to find any reference in the textbook or anywhere else where it states that there is atrial preload (in addition to the established ventricular preload), and I have not been able to come up with anything.

Page 698 of the text states:

"The CVP represents the

filling pressure of the right atrium and is a measurement of

right ventricular preload."

This seems to reinforce that, although atrial pressure or CVP is a good measurement for pre-load, it is not where the actual preload itself is located, which would be the ventricle. The only reason I make this differentiation is because of what follows next.

On page 241 of the text, in table 14-1, it defines CVP as "Pressure created by volume in the right side of the heart. When the tricuspid valve is open, the CVP reflects filling pressures in the right ventricle."

However, the exam question was about a stenotic valve, so the CVP wouldn't reflect the right ventricle (aka preload) in this case, it would actually be the opposite.

Further, on page 256 of the text, in reference to mitral valve stenosis, it states:

Mitral Stenosis. Pathology of the mitral valve-stenosis

or regurgitation-alters the accuracy of PAOP and PADP as

parameters of LV function. In mitral valve stenosis, LAP and

PAOP are increased and cause pulmonary congestion; however,

these elevated values do not reflect the LVEDP because a stenotic

mitral valve decreases normal blood flow from the left

atrium to the left ventricle, decreasing LV preload and consequently

lowering LVEDP. A nonstenotic mitral valve is essential

for accurate readings because a narrowed mitral valve increases

LAP, PAOP, and PADP in the presence of a normal LVEDP.

Even though it's talking about the left side of the heart above and the question on the exam was talking about the right side of the heart, I would think the same principle would apply.

Again, this is all assuming that, strictly defined, preload is referring to the volume only in the ventricles at end-diastole and not the atria. As I mentioned before, I cannot find any instance where it is stated that the atria also have a "preload", only that the CVP/RAP are a good indicator of what the right ventricular preload will be when the tricuspid valve is open.

I truly do not remember you saying anything about atrial preload vs ventricular preload in class and I don't see anything in the slides or the text. Though I fully understand the relationship between CVP/RAP and right ventricular preload, if preload itself is defined as only occurring in the ventricles (as evidenced by the text), then I feel that the exam question should be changed to NOT include tricuspid stenosis as something that increases preload, as it would actually be decreased.

Sorry for the long-winded e-mail and thanks again for listening and for your patience. See you in class Tuesday and I hope you have a great evening.

Sincerely,

XXXXX

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That's it for now. Am I crazy or am I right? I really like my professor and she's really amazing usually, but I really feel like I'm right on this one, if we are going by the textbook.

Thanks cardio people!

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