American Board of Surgery Qualifying Exam (ABS QE) Practice Test

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What is the effect of isoproterenol on cardiac output and vascular resistance?

Decreases cardiac output and increases vascular resistance
Increases cardiac output and vasodilates
Has no effect on either
Decreases cardiac output and vasodilates

The correct answer is: Increases cardiac output and vasodilates

Isoproterenol is a non-selective beta-adrenergic agonist that primarily stimulates beta-1 and beta-2 receptors. Its impact on the cardiovascular system is significant, particularly in relation to cardiac output and vascular resistance. When isoproterenol is administered, it results in an increase in heart rate and myocardial contractility due to its action on beta-1 receptors. This increase in heart rate and contractility leads to an elevation in cardiac output, which refers to the amount of blood the heart pumps in a minute. At the same time, isoproterenol also stimulates beta-2 receptors, which causes vasodilation, particularly in the peripheral vascular system. This vasodilation results in a decrease in systemic vascular resistance. The combination of increased cardiac output and decreased vascular resistance predominantly leads to an enhanced overall blood flow. This dual action - increasing cardiac output while causing vascular smooth muscle relaxation and subsequently reducing vascular resistance - is why the statement indicating that isoproterenol increases cardiac output and causes vasodilation is accurate.