Frank Starling Mechanism

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The Frank Starling Mechanism (FSM) describes an autonomous control circuit in the heart , namely the relationship between filling and ejection capacity: the larger the volume of blood flowing in during diastole , the greater the blood volume ejected during the following systole . “The heart pumps what it gets” , in other words: If the venous return flow is reduced, the stroke volume is also reduced. It was described by the physiologists Otto Frank and Ernest Starling on the isolated heart and later on the heart-lung preparation. The German internist and physiologist Hermann Straub was also involved . One therefore sometimes speaks of the Frank-Straub-Starling mechanism .


With an increasing filling of the auricles ( preload ), there is also an increase in the filling of the heart chambers and thus an increase in the stroke volume if the heart rate remains the same .

When the resistance of the blood outflow increases ( afterload ), on the other hand, the heart pumps at a higher pressure and can thus transport the same amount of blood as before at the same heart rate . This adjustment takes place in stages, in that at the end of the contraction phase ( systole ) more blood remains in the heart chamber due to the higher afterload. This back pressure leads to a stronger filling in the relaxation phase ( diastole ).

The strength of the heart muscle cells depends on the preload, i.e. on their preload before the start of the contraction. Within certain limits, the more the sarcomeres of the muscle cells are stretched, the higher it is. Due to the end-diastolic increase in volume, the actin and myosin filaments overlap optimally (from the original 1.9 µm sarcomere length to about 2.2 µm sarcomere length). This optimal overlap results in a maximum force of around 2.2 µm (some books also speak of 2.6 µm). This length is usually not exceeded in healthy people. If it is exceeded, the maximum force decreases again because the contractile elements no longer overlap in some cases.

With an optimal overlap area, calcium sensitization is effected in the myofibrils . The contractile apparatus becomes more sensitive to calcium. The usual calcium influx when an action potential develops is sufficient to cause a stronger reaction in the myofibrils.

The inflowing blood volume fluctuates with physical activity, with the body position ( orthostasis reaction ) and, in the case of rhythm disturbances, even from beat to beat. The Frank Starling mechanism ensures that the heart functions properly and that the ejection volumes of the right and left heart are mutually adjusted. This is particularly important for volume shifts within the body, such as the transition from standing to lying and in fluid transfusion (intravenous drip) in zero gravity and in the post-operation phase after heart transplants, because the new heart so completely denervated is and is therefore dependent on the mechanism.

The Frank Starling mechanism is used to automatically adapt the chamber activity to short-term pressure and volume fluctuations (change in preload and / or afterload) with the aim of ensuring that both chambers always pump the same stroke volume. For example, if the right heart were to pump only 1 ml more blood per beat, the difference would correspond to approx. 60 ml after one minute and would lead to pulmonary edema within a very short time .