Increase in stroke volume is a result of _______.

Increase in stroke volume is a result of _______.

• A. increased contractility
• B. increased EDV
• C. increased preload
• D. All of the above

Answer: (D)

Stroke volume rises when the ventricle either fills more or contracts more forcefully. Increasing contractility directly strengthens the heart’s squeeze, ejecting more blood with each beat. Increasing end-diastolic volume raises preload—the stretch on the ventricular muscle at the end of filling. A greater preload, through the Frank-Starling mechanism, produces a stronger contraction and a higher stroke volume. Since end-diastolic volume is a measure of preload, higher EDV means higher preload and thus higher SV as well. Therefore, both increased contractility and increased preload (via higher EDV) contribute to a larger stroke volume, making all the factors listed capable of increasing SV.

Stroke volume rises when the ventricle either fills more or contracts more forcefully. Increasing contractility directly strengthens the heart’s squeeze, ejecting more blood with each beat. Increasing end-diastolic volume raises preload—the stretch on the ventricular muscle at the end of filling. A greater preload, through the Frank-Starling mechanism, produces a stronger contraction and a higher stroke volume. Since end-diastolic volume is a measure of preload, higher EDV means higher preload and thus higher SV as well. Therefore, both increased contractility and increased preload (via higher EDV) contribute to a larger stroke volume, making all the factors listed capable of increasing SV.