Which statement best describes the mechanism behind orthostatic hypotension in immobility?

• A. Increased vasoregulation
• B. Normal vasoregulation
• C. Decreased vasoregulation
• D. Enhanced venous return

Answer: (C)

When standing, the body relies on rapid vasoconstriction to maintain blood pressure as venous blood pools in the legs. In immobility, the autonomic nervous system and vascular smooth muscle become less responsive, so the reflex that constricts peripheral vessels (vasoregulation) is blunted. This inadequate vasoconstriction means arterial pressure falls more easily when upright, producing orthostatic hypotension. The other ideas would either boost constriction, keep regulation normal, or improve return of blood to the heart, which would prevent the drop in pressure, so they don’t fit this mechanism.