What is preload in hemodynamics?

What is preload in hemodynamics?

• A. The amount of volume returned to the heart at the end of diastole
• B. The pressure in the aorta during systole
• C. The contractile force of the ventricle
• D. The resistance the ventricle pumps against

Answer: (A)

Preload is the volume of blood in the ventricle at the end of diastole, right before the heart contracts. It represents how much the ventricle has filled and thus how stretched the myocardial fibers are at the start of systole. This filling comes from venous return and is influenced by ventricular compliance. In practice, preload is often estimated by end-diastolic volume or end-diastolic pressure for the left ventricle (and by central venous pressure or pulmonary capillary wedge pressure for the right). The reason this choice is correct is that it specifically describes the filling phase that sets the initial stretch of the cardiac muscle, which governs how forcefully the heart can pump according to the Frank-Starling mechanism. By contrast, the pressure in the aorta during systole reflects afterload, the contractile force of the ventricle describes contractility, and the resistance the ventricle pumps against is afterload as well.

Preload is the volume of blood in the ventricle at the end of diastole, right before the heart contracts. It represents how much the ventricle has filled and thus how stretched the myocardial fibers are at the start of systole. This filling comes from venous return and is influenced by ventricular compliance. In practice, preload is often estimated by end-diastolic volume or end-diastolic pressure for the left ventricle (and by central venous pressure or pulmonary capillary wedge pressure for the right). The reason this choice is correct is that it specifically describes the filling phase that sets the initial stretch of the cardiac muscle, which governs how forcefully the heart can pump according to the Frank-Starling mechanism. By contrast, the pressure in the aorta during systole reflects afterload, the contractile force of the ventricle describes contractility, and the resistance the ventricle pumps against is afterload as well.