Which change would shift the Frank-Starling curve downward?

Which change would shift the Frank-Starling curve downward?

• A. Administration of a beta-blocker (negative inotropic)
• B. Administration of a positive inotropic drug
• C. Increasing preload
• D. Decreasing afterload

Answer: (A)

The key idea is that the Frank-Starling curve shows how much the heart can pump (stroke volume) for a given amount of filling (preload). The curve’s position is determined by contractility—the heart’s ability to generate force. When contractility falls, the ventricle can eject less blood for the same filling, so the entire curve shifts downward. Administering a beta-blocker reduces contractility (negative inotropy), so for any level of preload the stroke volume is lower, moving the curve downward. Increasing preload or moving along the curve simply changes the operating point along the same curve. A positive inotropic drug would raise the curve, increasing stroke volume at the same preload, while decreasing afterload alters the flow at a given preload but doesn’t shift the curve itself.

The key idea is that the Frank-Starling curve shows how much the heart can pump (stroke volume) for a given amount of filling (preload). The curve’s position is determined by contractility—the heart’s ability to generate force. When contractility falls, the ventricle can eject less blood for the same filling, so the entire curve shifts downward.

Administering a beta-blocker reduces contractility (negative inotropy), so for any level of preload the stroke volume is lower, moving the curve downward. Increasing preload or moving along the curve simply changes the operating point along the same curve. A positive inotropic drug would raise the curve, increasing stroke volume at the same preload, while decreasing afterload alters the flow at a given preload but doesn’t shift the curve itself.