After heart transplantation, which hemodynamic response is expected following the administration of phenylephrine?

The chosen response highlights a key physiological principle in the context of heart transplantation and the administration of phenylephrine, which is a selective alpha-1 adrenergic agonist. After heart transplantation, the autonomic innervation to the heart is disrupted, leading to changes in how the heart responds to vasoactive medications.

When phenylephrine is administered, it primarily causes vasoconstriction via alpha-1 receptor activation. This vasoconstriction typically results in an increase in blood pressure due to increased systemic vascular resistance. The correct option indicates that while blood pressure increases as expected, heart rate remains unchanged.

In a transplanted heart, the decrease or lack of response in heart rate occurs because the transplanted heart is devoid of autonomic nervous system innervation. As a consequence, the usual baroreceptor reflex that would normally decrease heart rate in response to an increase in blood pressure is absent. Therefore, despite the increase in blood pressure following phenylephrine administration, heart rate does not respond.

This understanding of hemodynamic responses following heart transplantation is crucial for anticipating patient responses to medications and managing postoperative care effectively.