Understanding The Frank – starling law of the heart
Ayinla Daniel Rn, Rctn (in view)
The Frank-Starling law, a very vital physiological law that every serious -minded nursing/medical practitioner should be familiar with.
This law explains the physiological relationship between the contractility of the heart muscles and the stroke volume.
In the late 19th century, Otto Frank found using isolated frog hearts that the strength of ventricular contraction was increased when the ventricle was stretched prior to contraction. This observation was extended by the elegant studies of Ernest Starling and colleagues in the early 20th century who found that increasing venous return to the heart, which increased the filling pressure (left ventricular end-diatolic pressure; LVEDP of the ventricle, led to increased stroke volume (SV). Conversely, decreasing venous return decreased stroke volume. This cardiac response to changes in venous return and ventricular filling pressure is intrinsic to the heart and does not depend on extrinsic neurohumoral mechanisms although such mechanisms can modify the intrinsic cardiac response. In honor of these two early pioneers, the ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return is called the Frank-Starling mechanism (or Starling’s Law of the heart).
Now, here are the vital points to note when describing the Frank – Starling Law.
• The Ventricular Preload
• The Stroke Volume
• Myocardial Contraction
• Central Venous Pressure
The heart muscles ability to stretch [myocardial contraction; during diastole, ventricular filling with an increase in ventricular preload] in response to the increased ventricular filling as a result of increased venous pressure [central venous pressure], summarises the Frank – Starlings law. With increase in preload [ventricular force at the end of diastole; heart muscle stretch/contract], there is an increased stroke volume [ amount of blood that leaves the ventricles per beat], so with increase preload, due to increased venous return there is increased stroke volume with resultant increase in cardiac output.