Haemodynamic and kinetic-triggered extracorporeal circulation in heart surgery

Mimicking the physiological characteristics of the circulatory system, puls atile bloodflow has also been introduced into extracorporeal perfusion to a void known postoperative complications. In a mathematical consideration of the situation bloodflow is seen as a function of time F(t) for approximatel y constant Vessel diameter over a given time. The kinetic energy of a colum n of blood produced by the heart-lung machine is transmitted directly to th e arterial circulation via the aorta. The nature of the energy release can give rise to both positive (organ perfusion) and negative (damage to endoth elium) effects. This study investigates how this energy release can be opti mised, using the following experimental approach. A Doppler flow-measuring probe is placed on the ascending aorta to monitor the extracorporeal circul ation. At the same time, the blood pressure is measured and converted to a pressure-flow curve via an A/D converter. On the basis of the parameters th us obtained, the energy released by the heart-lung machine is calculated. B y regulating the functional parameters of a new generation of heart-lung ma chines, the bloodflow can then be adapted to the physiological requirements . Within the pulse period (cycle) a 20 % rise phase ending in a slightly in creasing plateau is established. The energy increase within a cycle should not exceed 150 joules. To optimize the mode of functioning of the heart-lun g machine, we introduced the "energy-equivalent pressure" (EEP). Adaptation of the EEP to the physiological conditions required a Basic flow of 60% at a pulse rate of 60/min and a pulse duration of 35 % within the pulsatile f low interval.