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-   -   Effect of IV calcium bolus on cardiac output and venous return (https://www.usmle-forums.com/usmle-step-1-forum/3418-effect-iv-calcium-bolus-cardiac-output-venous-return.html)

doctorF 07-27-2010 03:04 PM

Effect of IV calcium bolus on cardiac output and venous return
 
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In the diagram shown, the straight lines represent the cardiac output and venous return curves of a healthy individual. The effect of an increased blood volume state, such as immediately after a blood transfusion, is represented by the dotted line. In contrast to the increased blood volume state, delivering an intravenous calcium bolus would result in:
A. Increased total peripheral resistance
B. Higher equilibrium point
C. Decreased mean systemic pressure
D. Decreased cardiac output
E. Lower equilibrium point

Attachment 865
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inder 07-28-2010 09:45 PM

I'd guess A?? because calcium will also cause vasoconstriction????

doctorF 07-29-2010 01:41 AM

no inder try again:)

khushboo 07-29-2010 03:10 AM

equilibrium point for wt??
is it a dot in graph where 2 curve cardiac output and venous return meet??
if it is then its B. Higher equilibrium point

doctorF 07-29-2010 06:48 AM

The correct answer is C.

Intravenous calcium has an immediate, positive inotropic effect on the heart. This shifts the cardiac output curve left and up. Calcium has effect on the venous return curve. Therefore, a patient with increased inotropy will have the same mean systemic pressures as a healthy individual.

By contrast, a patient with increased blood volume has a right shift of the venous return curve (as shown in the image), and thus would have a higher mean systemic pressure. Also, the equilibrium point in a patient with increased inotropy can be higher, unchanged, or decreased when compared to a patient with increased blood volume. The equilibrium point will depend on the magnitude of the shifts in cardiac output and venous return curves.

Changes in total peripheral resistance is determined by the shape of the venous return curve, so this is unaffected by injection of inotropic agents.


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