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Frank-Starling Law & Inotropic Agents

Frank-Starling Law

The Frank-Starling Law of the heart predicts the relationship between changes in end diastolic volume, i.e., preload, and stroke volume.

As left ventricular end-diastolic volume increases, so, too, does stroke volume.

This is because the volume of blood in the ventricle determines the degree of myofibril stretch; In turn, the degree of myofibril stretch, aka, the tension on the myofibril, determines the mechanical force produced by the myofibril during contraction.

And, as we know, the force of contraction determines how much blood is ejected from the ventricle.

Changes in contractility shift the Stroke Volume – End Diastolic Volume curve to the Right or Left.

Positive inotropic agents:

The sympathetic nervous system Adrenergic agonists Cardiac glycosides (such as digoxin) Angiotensin II Reduced sodium levels Increased heart rate

Several these agents act by increasing the intracellular calcium concentration; in their presence, stroke volume is increased at any given end diastolic volume.

Negative inotropic agents:

The parasympathetic nervous system Beta blockers Reduced intracellular calcium (and, therefore, calcium channel blockers) Some antiarrhythmics High sodium concentrations Reduced heart rate Thus, in the presences of these agents, stroke volume is decreased at any given end diastolic volume.

Frank-Starling Law & Inotropic Agents

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