Pulsator (half section and prototype)
Exemplary result of a measurement from an experiment with the Pulsator
The project presented here examines the research cooperation between the Institute for Product Development, Technische Universität München, and a cardiology centre in Munich, Deutsches Herzzentrum München. The main aim of the project was the optimization of the interaction of the heart lung machine (HLM) and the human organism. The extracorporeal circulation (ECC) - where the HLM takes over the blood circulation, gas exchange and thermoregulation of the blood outside of the body - belongs to the routine procedures of open heart surgery. Nowadays the control in clinical application takes place depending on the evaluation of hemodynamic pressure and flow ratio and chemical data from the laboratory. The control is based on the intuition and experiences of the surgeons, anaesthesiologist and cordiotechnician essentially. Until today no direct feedback between the actual values of the HLM and the reactions in the organism caused thereby exists. Target of the research project is the development of a system, which enables a more physiologic ECC through an improved adjustment to the human organism. In this way the risks and the after-effects of open heart surgery can be permanently reduced.
The developed pulsator is a simple piston pump, consisting of a cylinder and a piston with a flexible actuation and a programmable logic controller. A constant flow generated by the roller pump of a conventional HLM passes a cylinder. At the inlet of the pulsator is a non-return valve. If the piston is stopped, the blood still can flow through the pulsator to the patient. In this case there are the same haemodynamic pressure and flow ratio, as known from conventional ECC.
Generating a pulsation takes place in two phases, which are described subsequent:
Changes of the pressure and the flow rate can be set very individually by a variation of the speed, the stroke and the frequency of the piston’s motion. In this way and with an adequate control and high-dynamic mechanics a pulse can be copied.
After completion and technical verification of the prototype ten laboratory tests with young pigs were carried out. These first tests were necessary to improve the prototype and to gain experiences in handling the system. In consequence of the tests some constructional changes had to be made to reduce the pressure loss between pulsator and laboratory animal and the maximum pressure within the cylinder of the pulsator.
After this first test phase twelve standardized attempts were accomplished. All experiments ran according to the same pattern.
The evaluation of the measured data showed that it is possible to reproduce the pressure ratio with the pulsator to the greatest possible extent. The use of this was confirmed by the evaluation of first tissue specimen, which showed a improved blood circulation in the organs in relation to values of former experiments without pulsation.
To make a well-founded statement, actually experiments with conventional ECC are carried out. The results of these tests have to be compared with the results of the Pulsator tests.
In the context of this project it could be shown that the pulsators effects a clear improvement to the hemodynamic pressure and flow ratio. To verify this cognition, the results from the attempts with pulsation and from the attempts without pulsation must be compared. If the positive estimate could be confirmed, following measures must be taken, in order to improve the current design of the pulsator.
The system-costs, especially all the one-way parts, must be reduced.
Structure, test and certifying of an close-to-production prototype.
The development of the necessary mechanics was already continued. In the following pictures the developed new prototype is shown. It operates with a flexible membrane and a separation liquid (NaCl), which separates the blood of the piston. The unit corresponds in its dimensions with conventional HLM.
In this way the described project can be a contribution for the reduction of the consequential damage and the convalescence times after a heart surgery. This does not only lead to an improvement of the situation of the patient. This development can help to reduce the costs of the health insurance companies and thus for the public also.
Dipl.-Ing. Christoph Jung | TU Munich
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