Frank–Starling law of the heart

The Frank -Starling mechanism ( FSM) describes an autonomous control loop in the heart, namely the relationship between the filling and ejection fraction: the larger the volume of inflow during diastole blood, the greater the ejected during the subsequent systole blood volume. " The heart pumps what it gets ", in other words, is the venous return decreases, the stroke volume is also reduced. He was described by the physiologist Otto Frank and Ernest Starling on isolated hearts and later in the heart-lung preparation. Also involved was the German internist and physiologist Hermann Straub. One speaks therefore sometimes by Frank Straub -Starling mechanism.

Operation

With increasing filling of the atria ( preload ), there is also an increase in the filling of the ventricles and thus at constant heart rate to an increase in stroke volume.

With an increase in the resistance of the blood outflow ( afterload ), the heart pumps the other hand, at a higher pressure and can carry the same amount of blood as before, so at the same heart rate. This adaptation is performed in stages by first at the end of the contraction phase ( systole) more blood left by the higher afterload in the heart chamber. This back pressure results in more charge in the relaxation phase (diastole ).

The force of heart muscle cells is dependent on the pre-load, ie of its bias before the start of contraction. Within certain limits, it is the higher, the more the sarcomeres of muscle cells are stretched. By end-diastolic increase the volume to achieve optimum overlap of the actin and myosin filaments ( from the original 1.7 to 1.8 microns sarcomere length to about 2.0 to 2.2 microns sarcomere length ). This optimal overlap causes a maximum strength at about 2.2 microns ( other books also speak of 2.6 microns ). This length is usually not exceeded in healthy subjects.

With optimum overlap area a calcium sensitization is effected in the myofibrils. The contractile apparatus is sensitive to the calcium. So all it takes is the usual calcium influx in training of an action potential to cause a stronger reaction of the myofibrils.

The inflowing blood volume varies with physical activity, the body position ( orthostatic reaction ), and even from beat to beat in rhythm disorders. The Frank -Starling mechanism represents the proper heart function and the mutual adjustment of the ejection volumes of the right and left heart safe. This is especially for volume shifts within the body important for example in the transition from standing to lying down and in fluid transfusion ( intravenous infusions), in microgravity or in the post -operation phase after heart transplantation, as the new heart is so completely denervated and thus is dependent on the mechanism.

The Frank -Starling mechanism is used for automatic adjustment of chamber activities to short-term pressure and volume fluctuations (changes in pre-and / or afterload ) with the aim that both chambers always pump the same stroke volume. For example, if the right heart pumps blood more only 1 ml per beat, so the difference would after a minute already about 60 ml and would result in a very short time to pulmonary edema.