Preload refers to the ventricular end-diastolic volume (EDV), which represents the amount of blood filling the ventricles before contraction. It is primarily influenced by venous tone and circulating blood volume.
Factors Affecting Preload:
✅ Increased Preload With:
- Higher venous return due to increased circulating blood volume (e.g., IV fluids, blood transfusion).
- Venoconstriction, which pushes more blood toward the heart.
❌ Decreased Preload With:
- Venous vasodilators like nitroglycerin, which reduce venous return and lower preload.
- Conditions such as hypovolemia (e.g., hemorrhage, dehydration) that reduce blood volume.
Preload plays a crucial role in cardiac output by influencing the Frank-Starling mechanism, where greater ventricular filling leads to stronger contractions—up to a physiological limit.