Orthostatic hypotension is most directly caused by which of the following?

• A. Positional change reducing venous return
• B. Infection
• C. Allergic reaction
• D. Elevated fluid volume

Answer: (A)

When you move to an upright position, gravity pulls blood into the legs and abdomen, which reduces the amount of blood returning to the heart (venous return). With less blood returning, the heart’s preload drops, so stroke volume and cardiac output fall. If the body’s reflexes can’t compensate quickly enough by constricting veins and increasing heart rate, blood pressure drops, producing orthostatic hypotension. The direct cause is this positional reduction in venous return. Infections or allergic reactions can cause low blood pressure through other mechanisms (vasodilation, sepsis), and a high fluid volume would not cause the temporary drop seen with standing.