Which are the three variables that influence stroke volume?

Which are the three variables that influence stroke volume?

• A. Preload, contractility, afterload.
• B. Preload, heart rate, afterload.
• C. Venous return, arterial pressure, heart rate.
• D. End-systolic volume, contractility, afterload.

Answer: (A)

Stroke volume is determined by preload, contractility, and afterload. Preload reflects how much the ventricle fills; more venous return increases end-diastolic volume, stretches the heart muscle, and via the Frank-Starling mechanism increases the force of contraction, raising how much blood is ejected. Contractility is the heart’s intrinsic ability to contract; stronger contractility means more complete emptying, lowering end-systolic volume and boosting stroke volume. Afterload is the pressure the ventricle must overcome to eject blood; when afterload is high, the heart pumps against greater resistance, and stroke volume falls because less blood is ejected. Heart rate influences cardiac output but does not directly set stroke volume, and end-systolic volume is a consequence of the interplay of preload, contractility, and afterload rather than an independent determinant of stroke volume.

Stroke volume is determined by preload, contractility, and afterload. Preload reflects how much the ventricle fills; more venous return increases end-diastolic volume, stretches the heart muscle, and via the Frank-Starling mechanism increases the force of contraction, raising how much blood is ejected. Contractility is the heart’s intrinsic ability to contract; stronger contractility means more complete emptying, lowering end-systolic volume and boosting stroke volume. Afterload is the pressure the ventricle must overcome to eject blood; when afterload is high, the heart pumps against greater resistance, and stroke volume falls because less blood is ejected.

Heart rate influences cardiac output but does not directly set stroke volume, and end-systolic volume is a consequence of the interplay of preload, contractility, and afterload rather than an independent determinant of stroke volume.