Increasing the left flow tube radius corresponds to which change?

Increasing the left flow tube radius corresponds to which change?

• A. Increasing afterload
• B. Increasing preload
• C. Increasing heart rate
• D. Decreasing afterload

Answer: (B)

Increasing the left flow tube radius lowers the resistance to flow coming into the left heart. With a given driving pressure, that means more blood can return to and fill the left ventricle during diastole. The amount of blood filling the ventricle sets the end-diastolic volume, which is what preload measures. Because flow through a tube scales strongly with radius (Poiseuille’s law: flow ∝ radius^4), even a modest widening can markedly boost venous return and thus preload. In this context, the change is interpreted as an increase in preload rather than a change in heart rate or intrinsic contractility.

Increasing the left flow tube radius lowers the resistance to flow coming into the left heart. With a given driving pressure, that means more blood can return to and fill the left ventricle during diastole. The amount of blood filling the ventricle sets the end-diastolic volume, which is what preload measures. Because flow through a tube scales strongly with radius (Poiseuille’s law: flow ∝ radius^4), even a modest widening can markedly boost venous return and thus preload. In this context, the change is interpreted as an increase in preload rather than a change in heart rate or intrinsic contractility.