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PubMed2002

Observer design for haemodynamics in patients undergoing cardiac surgery.

During extracorporeal circulation, many important circulatory parameters are unknown, being inaccessible for measuring probes, as e.g. the perfusion of the brain. An observer system, which estimates such patient variables continuously throughout the operation, can extend the information basis for the decisions of the perfusionist regarding the control of the heart-lung machine and thus contribute to adjust this operation procedure to the actual patient situation. The observer design is based on a mathematical model of the human circulatory system. Beside the classical Luenberger observer design, a rule-based approach has been tested, which is also based on the structure of a Luenberger observer, however instead of an observer matrix a correction algorithm has been used in the feedback loop. A prototype of this system for animal experimental and clinical evaluation has been realised.

Algorithms↗

PubMed2002

[Multi-value regulatory systems for extracorporeal circulation].

Extracorporeal perfusion is the standard technique in cardiac surgery. It is controlled by perfusionists on the basis of their clinical experience and on the available data collected pre- and intra-operatively. But in spite of intensive monitoring postoperative complications occur. An appropriate control of the heart-lung machine (HLM) using an "autopilot" might improve the quality of heart-surgery and decrease postoperative complications. Hence, a mathematical model of a human circulatory system has been developed which provides much more information about haemodynamics, blood gases and acid-base status than standard monitoring. It has been implemented on a system which is capable of integrating measured data as input parameters in real-time in the simulation. Now, soft- and hardware control concepts based on the human circulatory system have to be developed which are able to control the HLM.

Coronary Disease↗

PubMed1999

Mathematical modelling of extracorporeal circulation: simulation of different perfusion regimens.

Computer- and sensor-aided control of the heart-lung machine is considered a major goal for perfusion sciences for the next few years. At present, control of perfusion is achieved by surgeons, anaesthesiologists and perfusionists making short-term decisions, which leads to variations of the perfusion regimens between different centres and even between different teams in the operating theatre. As the basis for an integrated control of extracorporeal circulation (ECC), we proposed a mathematical model for simulating haemodynamics during pulsatile perfusion. This model was then modified to allow it to simulate the effects of different perfusion regimens on arterial haemodynamics and whole body oxygen consumption. The model was constructed on a PC using MATLAB/SIMULINK. The human arterial tree was divided into a multibranch structure consisting of 128 segments characterized by their particular physical properties. Peripheral branches were terminated by a resistance term representing smaller vessels like arterioles and capillaries. Flow and pressure were expressed by the intensity of current and voltage in an electrotechnical analogon; inductivity, resistance and capacitance were implemented according to the physical properties of the arterial tree and the rheology of blood. The effects of different perfusion regimens (pulsatility, flow amount, acid-base regulation) were studied. After introducing an input signal to the model, flow and pressure waves established themselves throughout the simulated arterial tree. During the simulation experiments, marked differences among different perfusion regimens were displayed by the model. Variations in acid-base management mainly influenced the distribution of perfusion: during simulation of low-flow perfusion (1.2 l/min/m2), cerebral blood flow was 6.2 ml/s using an alpha-stat regimen, while it was increased to 9.4 ml/s during pH-stat, caused by an implementation of reduced cerebral resistance. Whole body oxygen consumption was predominantly regulated by the perfusion rate. While central venous oxygen saturation was calculated to be 84.7% during simulation of high-flow perfusion (2.4 l/min/m2), it dropped to 70% during simulation of low-flow perfusion regimens. The model proved to be useful for a realistic simulation of different perfusion regimens. Therefore it can be considered a continuing step for the derivation of a 'state' observer leading to the realization of an automatically controlled heart-lung machine.

Blood Transfusion↗