Which factors influence stroke volume?

Which factors influence stroke volume?

• A. Preload, contractility, and afterload.
• B. Heart rate, respiratory rate, and blood viscosity.
• C. Atrial pressure, venous return, and ventricular compliance.
• D. Oxygen demand, coronary perfusion, and systemic vascular resistance.

Answer: (A)

Stroke volume is determined by preload, contractility, and afterload. Preload is the volume entering the ventricle at end diastole; more filling stretches the cardiac fibers and, via the Frank-Starling mechanism, increases the force of contraction and the amount ejected. Contractility refers to the intrinsic strength of the ventricular muscle; when contractility is higher, the heart pumps more blood with each beat, increasing stroke volume. Afterload is the pressure the ventricle must overcome to eject blood; higher afterload makes ejection harder and decreases stroke volume, while lower afterload allows more complete ejection and raises stroke volume. Other factors listed are not the primary determinants of stroke volume. Heart rate affects cardiac output (not SV directly); respiratory rate and viscosity influence hemodynamics in more indirect ways. Atrial pressure and ventricular compliance relate to filling (and can alter preload) but do not define the core trio as clearly as preload, contractility, and afterload. Oxygen demand and perfusion relate to coronary physiology and supply rather than the basic mechanics setting the amount pumped per beat.

Stroke volume is determined by preload, contractility, and afterload. Preload is the volume entering the ventricle at end diastole; more filling stretches the cardiac fibers and, via the Frank-Starling mechanism, increases the force of contraction and the amount ejected. Contractility refers to the intrinsic strength of the ventricular muscle; when contractility is higher, the heart pumps more blood with each beat, increasing stroke volume. Afterload is the pressure the ventricle must overcome to eject blood; higher afterload makes ejection harder and decreases stroke volume, while lower afterload allows more complete ejection and raises stroke volume.

Other factors listed are not the primary determinants of stroke volume. Heart rate affects cardiac output (not SV directly); respiratory rate and viscosity influence hemodynamics in more indirect ways. Atrial pressure and ventricular compliance relate to filling (and can alter preload) but do not define the core trio as clearly as preload, contractility, and afterload. Oxygen demand and perfusion relate to coronary physiology and supply rather than the basic mechanics setting the amount pumped per beat.