Drugs that cause vasodilation can contribute to postural hypotension due to which mechanism?

Drugs that cause vasodilation can contribute to postural hypotension due to which mechanism?

• A. Decreased heart rate
• B. Vasodilation
• C. Increased peripheral resistance
• D. Increased myocardial contractility

Answer: (B)

Vasodilation lowers systemic vascular resistance and arterial pressure. When you stand, gravity pulls blood into the legs, reducing venous return. Normally the body counters this with reflex vasoconstriction and a faster heart rate to maintain blood pressure. If vessels are already dilated by a drug, these compensatory mechanisms can’t raise the pressure enough, so standing causes a larger drop in blood pressure—orthostatic or postural hypotension. Other options would not explain this effect: decreased heart rate would lower BP further but isn’t the mechanism of vasodilators; increased peripheral resistance or increased myocardial contractility would raise BP and counteract hypotension.

Vasodilation lowers systemic vascular resistance and arterial pressure. When you stand, gravity pulls blood into the legs, reducing venous return. Normally the body counters this with reflex vasoconstriction and a faster heart rate to maintain blood pressure. If vessels are already dilated by a drug, these compensatory mechanisms can’t raise the pressure enough, so standing causes a larger drop in blood pressure—orthostatic or postural hypotension. Other options would not explain this effect: decreased heart rate would lower BP further but isn’t the mechanism of vasodilators; increased peripheral resistance or increased myocardial contractility would raise BP and counteract hypotension.