A healthy volunteer receives an intravenous bolus of isoproterenol. Which haemodynamic pattern is expected?

• A Increased systolic, increased diastolic and decreased heart rate
• B Decreased systolic, decreased diastolic and decreased heart rate
• C Markedly increased systolic and diastolic pressures with reflex bradycardia
• D Slightly increased systolic pressure, markedly decreased diastolic pressure, and marked tachycardia ✓

Explanation

Isoproterenol is a non-selective beta agonist with no alpha activity. Beta-1 stimulation increases contractility and heart rate, raising systolic pressure modestly, while beta-2 stimulation dilates skeletal muscle vasculature, dropping diastolic and mean arterial pressure. The fall in mean pressure triggers baroreceptors, but direct beta-1 chronotropy dominates, so heart rate rises markedly rather than showing reflex slowing. Options A and C match epinephrine or norepinephrine patterns.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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