Which hemodynamic consequence is associated with phenylephrine due to its pure alpha-1 vasoconstriction?

Which hemodynamic consequence is associated with phenylephrine due to its pure alpha-1 vasoconstriction?

• A. Increased heart rate
• B. Decreased systemic vascular resistance
• C. Improved renal perfusion
• D. Decreased stroke volume and cardiac output

Answer: (D)

Phenylephrine provides pure alpha-1 vasoconstriction, so the main hemodynamic change is an increase in systemic vascular resistance and afterload. When afterload rises, the ventricle has to work harder to eject blood, which tends to lower stroke volume. The higher blood pressure also triggers baroreceptors, producing a reflex decrease in heart rate that further reduces cardiac output. So the combination of reduced stroke volume and a slower heart rate leads to decreased cardiac output, which is the correct concept here. Increased heart rate would not be expected with pure alpha-1 vasoconstriction—baroreceptor reflexes usually slow the rate. Systemic vascular resistance would increase, not decrease. Renal perfusion is not improved by this mechanism; higher afterload can actually reduce renal blood flow.

Phenylephrine provides pure alpha-1 vasoconstriction, so the main hemodynamic change is an increase in systemic vascular resistance and afterload. When afterload rises, the ventricle has to work harder to eject blood, which tends to lower stroke volume. The higher blood pressure also triggers baroreceptors, producing a reflex decrease in heart rate that further reduces cardiac output. So the combination of reduced stroke volume and a slower heart rate leads to decreased cardiac output, which is the correct concept here.

Increased heart rate would not be expected with pure alpha-1 vasoconstriction—baroreceptor reflexes usually slow the rate. Systemic vascular resistance would increase, not decrease. Renal perfusion is not improved by this mechanism; higher afterload can actually reduce renal blood flow.