Systemic vasodilation primarily lowers afterload. What is the typical effect on mean arterial pressure if cardiac output does not rise to compensate?

• A. Vasodilation lowers afterload and often reduces mean arterial pressure unless CO increases to compensate.
• B. Increases afterload and arterial pressure.
• C. Has no effect on afterload.
• D. Raises mean arterial pressure regardless of CO.

Answer: (D)

Systemic vasodilation lowers the resistance the heart has to push against, i.e., afterload decreases because systemic vascular resistance falls. Mean arterial pressure depends on how hard the heart pumps (cardiac output) and how much resistance the vessels offer (systemic vascular resistance). If cardiac output remains unchanged, lowering vascular resistance reduces MAP because MAP ≈ CO × SVR. So the typical effect is a fall in mean arterial pressure unless CO rises to compensate. Choices that claim afterload increases, no effect on afterload, or that MAP rises regardless of CO don’t fit this relationship.