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Automatic control of the extra-corporal bypass: system analysis, modelling and evaluation of different control modes
M Hexamer1, B Misgeld, A Prenger-Berninghoff
1Department of Biomedical Engineering, Medical Faculty, University Center of Medical Engineering, Ruhr-University Bochum, Germany. hexamer@biomed.rub.de
Biomedizinische Technik. Biomedical Engineering
|December 31, 2004
Summary
Automated control of blood gases during extracorporeal circulation is feasible. Adding feed-forward control significantly improves system performance and reduces errors, even with complex algorithms.
Area of Science:
- Biomedical Engineering
- Control Systems Engineering
- Physiological Monitoring
Background:
- Extracorporeal circulation (ECC) requires precise blood gas management.
- Manual control of blood gases during ECC is labor-intensive and prone to variability.
- Existing control systems face challenges due to process gain variations and flow-dependent dynamics.
Purpose of the Study:
- To develop and evaluate an automated control system for blood gas parameters during ECC.
- To identify and address control challenges in standard clinical ECC setups.
- To improve the efficiency and safety of ECC procedures through advanced control strategies.
Main Methods:
- Modeling of the ECC system, including blood and gas flow dynamics.
- Design of scheduled proportional-integral (PI) controllers for arterial oxygen and carbon dioxide partial pressures, scheduled by blood flow rate.
- Simulation-based testing of the control system under various operating conditions.
- Implementation and evaluation of a feed-forward control path based on blood flow rate and hemoglobin content.
Main Results:
- Scheduled PI controllers ensured system stability across tested conditions.
- Abrupt changes in blood flow rate led to significant load errors with PI control alone.
- The addition of a feed-forward control path markedly improved system performance and reduced errors.
- Feed-forward compensation proved effective even when integrated with sophisticated control algorithms.
Conclusions:
- Automated control of blood gases during ECC is achievable and beneficial.
- Feed-forward control is crucial for mitigating load errors caused by blood flow variations.
- Direct feed-forward compensation should be incorporated, regardless of the primary control algorithm used in ECC.