Some Applications of Self-Tuning Control to Blood Pressure Regulation

Abstract

A review is given of our investigations and experiences with self-tuning control of blood pressure during surgery. Phenylephrine infusions were used for restoration and maintenance of normal arterial pressure during epidural analgesia in lower abdominal surgery. Sodium nitroprusside infusions or inspired concentrations of the volatile anaesthetic agent isoflurane were used for inducing hypotension during plastic, neuro or ENT surgery. The approach was based on the generalized minimum-variance self-tuning controller of Clarke and Gawthrop. Recursive least-squares type estimation of controller parameters was performed, latterly with a restricted exponential forgetting identification technique to provide a more adaptive algorithm. Use of an anti-aliasing digital prefilter and an outlier detector to improve signal conditioning, and the application of constraints to the permitted parameter values enhanced the closed-loop system robustness. The controller using isoflurane performed as well as the best possible manual control obtainable by an anaesthetist, even when conditions provided by supplementary anaesthetic agents differed from the ideal. The method therefore proved useful for comparing the effect of various treatments under controlled conditions. Insight was also gained regarding the diagnosis of possible faults to ensure system integrity in this clinical context.