Which factors influence stroke volume?

Which factors influence stroke volume?

• A. Preload, contractility, afterload
• B. Only heart rate
• C. Only stroke volume
• D. Vascular compliance

Answer: (A)

Stroke volume is shaped by three main influences: preload, contractility, and afterload. Preload is the filling stretch of the heart at the end of diastole, determined by venous return and filling pressures. When preload increases, the cardiac muscle fibers are stretched more, which strengthens contraction and increases the amount of blood ejected (the Frank-Starling mechanism) up to a limit. Contractility is the heart’s intrinsic ability to generate force. Higher contractility boosts the force of contraction for the same preload, raising stroke volume. Afterload is the pressure the ventricle must overcome to open the aortic valve and push blood into the circulation. When afterload rises, ejection is harder, so stroke volume falls; when afterload falls, stroke volume tends to rise. Heart rate does not directly fix stroke volume (though it changes cardiac output since CO = SV × HR). Vascular compliance affects the arterial system and venous return indirectly, mainly through how filling pressures change, but the primary direct determinants of stroke volume are preload, contractility, and afterload.

Stroke volume is shaped by three main influences: preload, contractility, and afterload. Preload is the filling stretch of the heart at the end of diastole, determined by venous return and filling pressures. When preload increases, the cardiac muscle fibers are stretched more, which strengthens contraction and increases the amount of blood ejected (the Frank-Starling mechanism) up to a limit. Contractility is the heart’s intrinsic ability to generate force. Higher contractility boosts the force of contraction for the same preload, raising stroke volume. Afterload is the pressure the ventricle must overcome to open the aortic valve and push blood into the circulation. When afterload rises, ejection is harder, so stroke volume falls; when afterload falls, stroke volume tends to rise.

Heart rate does not directly fix stroke volume (though it changes cardiac output since CO = SV × HR). Vascular compliance affects the arterial system and venous return indirectly, mainly through how filling pressures change, but the primary direct determinants of stroke volume are preload, contractility, and afterload.