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III. The Frank-Starling Law of the Heart
Otto Frank (circa 1890) is credited with the seminal observation that peak
ventricular pressure increases as the end-diastolic volume is increased.
This observation was made in an isolated frog heart preparation in which
ventricular volume could be measured with relative ease. Around the mid
1910's, Starling and coworkers observed a related phenomenon, which they
presented in a manner that was much more useful to physiologists and
ultimately to clinicians. They measured the relationship between
ventricular filling pressure (related to end-diastolic volume) and cardiac
output.
The observations of Frank and of Starling form one of the basic concepts
of cardiovascular physiology: Cardiac performance (its ability to
generate pressure or to pump blood) increases with preload. However,
factors other than preload are important for determining cardiac
performance: ventricular contractility and afterload properties. Both of
these factors can influence the Frank-Starling Curves.
1. Use the "Filling Pressure" slider to vary preload, and then plot the
relationship of EDV and CO. Plot at least 5 different points. This curve
will represent the ^+baseline^+ Starling curve.
2. Change ventricular contractility and generate a new Starling curve. How do the two curves differ?
3. Return contractility back to baseline and now change ventricular afterload. How does afterload affect the Starling curve?