Stroke volume is determined by which of the following?

Stroke volume is determined by which of the following?

• A. Venous return, inotropic agents, and afterload.
• B. Heart rate only.
• C. Atrial contraction alone.
• D. Blood viscosity only.

Answer: (A)

Stroke volume is set by how much the ventricle fills, how strongly it contracts, and the pressure it must overcome to eject blood. More venous return increases preload, and through the Frank-Starling mechanism the heart ejects more with greater filling, raising stroke volume. If contractility is stronger (positive inotropy), the ventricle contracts more forcefully and pumps out more blood, increasing stroke volume. Conversely, higher afterload—the pressure in the arteries the ventricle must push against—makes ejection harder and tends to reduce stroke volume if filling and contractility don’t change. Heart rate by itself doesn’t determine stroke volume (it changes cardiac output rather than the amount ejected per beat), and atrial contraction or blood viscosity alone do not define stroke volume in isolation.

Stroke volume is set by how much the ventricle fills, how strongly it contracts, and the pressure it must overcome to eject blood. More venous return increases preload, and through the Frank-Starling mechanism the heart ejects more with greater filling, raising stroke volume. If contractility is stronger (positive inotropy), the ventricle contracts more forcefully and pumps out more blood, increasing stroke volume. Conversely, higher afterload—the pressure in the arteries the ventricle must push against—makes ejection harder and tends to reduce stroke volume if filling and contractility don’t change. Heart rate by itself doesn’t determine stroke volume (it changes cardiac output rather than the amount ejected per beat), and atrial contraction or blood viscosity alone do not define stroke volume in isolation.