A patient is having a surgical procedure and is given a large amount of IV (intr

Question

A patient is having a surgical procedure and is given a large amount of IV (intravenous) fluids. As a result, she actually ends up with a larger volume of blood than normal. (5 points total)

How would this addition of blood volume affect venous return (VR), SV, CO and MAP? Explain the full mechanism (each individual step) for the changes. Include explanations of the relationship between CO, HR and SV and between MAP, CO, and TPR. (4 points, 100 words)

What is the name of the mechanism that leads to changes in SV and CO? (1 point, 15 words)

Explanation / Answer

Answer

VR = CO

at constant physiological condition.

Now, at increased preload, i.e. increased blood volume , stroke volume will increase in response to an increase in VR (the end diastolic volume) when all other factors remain constant.

To accomodate the extravolume, myocardial fibrils of blood vessels stretch the ventricular wall, which leads to contract more forcefully and increase the CO.

The relationship between Stroke volume (SV), Heart Rate (HR), Mean Right Atrial Pressure in mmHg (MAP), Total Peripheral Resistance (TPR) are as follows,

SV x HR = CO = MAP/ TPR

thus, at constant HR , SV increases to accomodate extra fluid volume. Where as, due to vasodialation,, to accomodate the extra volume of fluid, as we have considered HR as constant, thus we say TPR wil be decreased.

Frank Starling Mechanism leads to the changes in SV and CO.

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