Preload is largely determined by end-diastolic volume; higher EDV stretches the ventricles more and increases preload. Which statement best describes preload?

Preload is largely determined by end-diastolic volume; higher EDV stretches the ventricles more and increases preload. Which statement best describes preload?

• A. Preload is largely determined by end-diastolic volume; higher EDV stretches the ventricles more and increases preload
• B. Preload equals end-systolic volume
• C. Preload is determined by heart rate
• D. Preload is independent of EDV

Answer: (A)

Preload is the initial stretch of the ventricular muscle fibers just before they contract, and it’s set primarily by the end-diastolic volume—the amount of blood in the ventricle at the end of filling. When the end-diastolic volume is higher, the ventricles are more stretched when they start to contract, which increases preload. This stretch-to-force relationship underlies the Frank-Starling mechanism: up to a point, greater preload leads to a stronger contraction and a higher stroke volume. So the statement that preload is largely determined by end-diastolic volume, with higher EDV stretching the ventricles more and increasing preload, is the best description. End-systolic volume is the amount left after contraction, not preload. Heart rate can influence filling time and venous return indirectly, but preload itself is not defined by heart rate. And preload is not independent of EDV; it depends on how much blood is in the ventricle at the end of filling.

Preload is the initial stretch of the ventricular muscle fibers just before they contract, and it’s set primarily by the end-diastolic volume—the amount of blood in the ventricle at the end of filling. When the end-diastolic volume is higher, the ventricles are more stretched when they start to contract, which increases preload. This stretch-to-force relationship underlies the Frank-Starling mechanism: up to a point, greater preload leads to a stronger contraction and a higher stroke volume.

So the statement that preload is largely determined by end-diastolic volume, with higher EDV stretching the ventricles more and increasing preload, is the best description. End-systolic volume is the amount left after contraction, not preload. Heart rate can influence filling time and venous return indirectly, but preload itself is not defined by heart rate. And preload is not independent of EDV; it depends on how much blood is in the ventricle at the end of filling.