In hypotension, phenylephrine increases coronary perfusion pressure without altering which parameter?

In hypotension, phenylephrine increases coronary perfusion pressure without altering which parameter?

• A. Contractility
• B. Heart rate
• C. Blood pressure
• D. Aortic impedance

Answer: (A)

Phenylephrine works mainly by constricting peripheral arteries through alpha-1 receptors, which raises systemic vascular resistance and diastolic aortic pressure. Coronary perfusion pressure (CPP) depends on the diastolic aortic pressure minus right atrial pressure, so boosting diastolic pressure improves CPP without needing to increase the heart’s pumping force. It does not directly stimulate beta receptors, so there’s no increase in myocardial contractility; the heart’s intrinsic ability to contract isn’t enhanced by phenylephrine. In fact, the higher afterload from vasoconstriction can influence cardiac work, but contractility itself isn’t the target or directly changed. Heart rate often decreases via a reflex bradycardia to the rise in blood pressure, and blood pressure itself rises, while aortic impedance (afterload) increases from the vasoconstriction. Put together, the parameter that remains effectively unchanged is contractility.

Phenylephrine works mainly by constricting peripheral arteries through alpha-1 receptors, which raises systemic vascular resistance and diastolic aortic pressure. Coronary perfusion pressure (CPP) depends on the diastolic aortic pressure minus right atrial pressure, so boosting diastolic pressure improves CPP without needing to increase the heart’s pumping force.

It does not directly stimulate beta receptors, so there’s no increase in myocardial contractility; the heart’s intrinsic ability to contract isn’t enhanced by phenylephrine. In fact, the higher afterload from vasoconstriction can influence cardiac work, but contractility itself isn’t the target or directly changed.

Heart rate often decreases via a reflex bradycardia to the rise in blood pressure, and blood pressure itself rises, while aortic impedance (afterload) increases from the vasoconstriction. Put together, the parameter that remains effectively unchanged is contractility.