Which parameter primarily determines afterload in the systemic circulation?

Which parameter primarily determines afterload in the systemic circulation?

• A. Preload
• B. Pulmonary vascular resistance
• C. Systemic vascular resistance
• D. Heart rate

Answer: (C)

Afterload is the pressure the left ventricle must generate to eject blood during systole. In the systemic circulation, this pressure is set mainly by the tone of the systemic arterioles, i.e., the systemic vascular resistance. When arterioles constrict, systemic vascular resistance rises, increasing afterload and making it harder for the ventricle to eject blood. Preload reflects venous return and filling, not the pressure to overcome during ejection. Heart rate affects cardiac output and perfusion timing but not the main pressure the ventricle must overcome. Pulmonary vascular resistance is the afterload for the right ventricle, not the systemic circulation. Thus, systemic vascular resistance is the primary determinant of systemic afterload.

Afterload is the pressure the left ventricle must generate to eject blood during systole. In the systemic circulation, this pressure is set mainly by the tone of the systemic arterioles, i.e., the systemic vascular resistance. When arterioles constrict, systemic vascular resistance rises, increasing afterload and making it harder for the ventricle to eject blood. Preload reflects venous return and filling, not the pressure to overcome during ejection. Heart rate affects cardiac output and perfusion timing but not the main pressure the ventricle must overcome. Pulmonary vascular resistance is the afterload for the right ventricle, not the systemic circulation. Thus, systemic vascular resistance is the primary determinant of systemic afterload.