Automatic control of the blood gas parameters during extracorporeal circulation has the potential to improve the quality of this procedure and to relieve the personnel from a time consuming task. This paper describes a model of the underlying system for a standard clinical set-up and pinpoints the major difficulties which are the variations of the process gains and the blood- and gas-flow dependent dead times and time constants. Scheduled PI-controllers both for the arterial oxygen as well as for the carbon dioxide partial pressure were designed. Scheduling was based on the blood flow rate. These controllers were tested in a simulation environment. The control systems remained stable under all tested operating condition, but if the blood flow rate was changed abruptly rather large load errors occurred. The performance was improved markedly by adding a feed-forward control path which directly influences the actuating signals based on the actual blood flow rate and the hemoglobin contents, variables which are measured anyway. The major conclusion of this study is to use such direct feed-forward compensation even if more sophisticated control algorithms are used.
Explantierte Herzen können durch Nachbildung physiologischer Bedingungen isoliert im schlagenden Modus betrieben werden. Diese Eigenschaft bietet die Möglichkeit, umfangreiche Ganztierversuche durch Untersuchungen am isolierten Organ zu ersetzen und stellt gleichzeitig eine alternative Organtransportmethode bei Herztransplantationen dar. Dieser Beitrag stellt zwei Prototypen zu den genannten Anwendungsmöglichkeiten vor. Der Schwerpunkt liegt dabei in der Optimierung der Systeme durch Anwendung mess-und regelungstechnischer Methoden.If provided with adequate physiological conditions explanted hearts may continue to operate in beating mode. This property offers the opportunity to substitute extensive animal experiments by investigations on the isolated organ and at the same time it represents an alternative method for the transport of donor hearts for transplantation. Experimental setups for both applications are described in this paper. The focus is laid on optimisation of the experimental equipment by using measurement and control engineering methods.
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