The Frank-Starling law is fundamental to critical care. It describes the relationship between cardiac filling and cardiac contraction - essentially more filling = more contraction.
In normal physiology it means that output from the left heart matches output from the right heart - over a period of a few beats.
In critical care, it means that if we give a fluid-responsive patient fluid, then their cardiac output will increase.
The diagram above is plotted the opposite way round to the way it's generally drawn these days, and shows cardiac output on the x-axis, and filling pressure on the y-axis. It's from Patterson and Starling (1914) and shows the cardiac output from a number of unfortunate dogs as they varied the cardiac filling pressure. The key point being that as filling pressure increased so did output, though this fell off at a certain point. Equally important though is the considerable variation between different dogs. Although this was an experimental preparation the principle applies to humans in ICU - a particular filling pressure (i.e. CVP) does not mean a particular cardiac output.
Patterson SW, Starling EH (1914) On the mechanical factors which determine the output of the ventricles. J Physiol 48:357 – 379. Available from: https://doi.org/10.1113/jphysiol.1914.sp001669 (accessed 01.08.2024)
No comments:
Post a Comment