The FrankโStarling law, described by Otto Frank and Ernest Starling, explains how the heart adjusts its output. It states that:
"as more blood fills the ventricles (โ preload), the heart pumps more forcefully, increasing stroke volume "
In the graph:
๐ต Normal curve: Stroke volume increases with preload, then levels off.
๐ข Improved function: With better contractility or lower afterload, the heart pumps more efficiently.
๐ด Poor function: In heart failure (โ contractility or โ afterload), stroke volume increases slightly, then drops ("falling off").
๐ต Giving fluids only helps in the preload-dependent zone. Beyond that, it may worsen function.
๐ต The lowest curve shows cardiogenic shock, where extra preload barely helps.
Clinical use: Helps guide fluid therapy and avoid overload in heart failure.