A subject receives an intravenous infusion of isoproterenol. Which combination of haemodynamic changes is expected?
- A Decreased heart rate, increased diastolic pressure, narrowed pulse pressure
- B Increased heart rate, decreased diastolic pressure, widened pulse pressure ✓
- C Increased heart rate, increased diastolic pressure, reflex bradycardia
- D No change in heart rate, marked fall in both systolic and diastolic pressures
Correct answer: B. Increased heart rate, decreased diastolic pressure, widened pulse pressure
Explanation
Isoproterenol is a non-selective beta agonist with negligible alpha activity. Cardiac beta-1 stimulation raises heart rate and contractility, lifting systolic pressure, while beta-2 mediated skeletal muscle vasodilatation lowers diastolic pressure sharply. The result is a widened pulse pressure and prominent tachycardia driven both directly and by baroreflexes. Diastolic pressure rises only with alpha-mediated vasoconstriction, which isoproterenol lacks entirely.
Reference: Ganong Review of Medical Physiology, 26th ed.
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