USMLE Forums - View Single Post - Effect of IV calcium bolus on cardiac output and venous return
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Old 07-29-2010
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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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