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Biomedical subjects

D A Linkens

Publications and source records attributed to D A Linkens.

At least 37 records · Page 2Linked to original sources
PubMed1996

Performance assessment of a fuzzy controller for atracurium-induced neuromuscular block.

The performance of a fuzzy controller for atracurium-induced neuromuscular block was assessed. Ten ASA I or II patients undergoing surgery anticipated to last at least 120 min were studied. A Datex Relaxograph was used to monitor neuromuscular block. Initially the T1 set point was set at 10% of baseline for at least 30 min (phase I). The T1 set point was then increased to 20% and then returned to 10% for two further periods of at least 30 min duration (phases II and III). The mean (SD) of the mean T1 error in 10 patients for phases I, II and III were 1.1 (1.4)%, -0.43 (1.2)% and 0.28 (0.94)%, respectively. The results show that a simple fuzzy logic controller can provide good accuracy with insensitivity to set point changes despite the considerable inter-individual variation in infusion rate required.

Adult↗
PubMed1993

Neural networks and nonlinear regression modelling and control of depth of anaesthesia for spontaneously breathing and ventilated patients.

Various attempts have been made to control the depth of anaesthesia by observing different variables. In some studies, depth of anaesthesia has been correlated with inferential parameters and the control has been made through these inferred parameters. No single system has been reported which provides a fully developed architecture to control the depth of anaesthesia. This study is concerned with the development of controllers and patient models via Artificial Neural Networks and regression analysis. Two types of data sets were used for the training and development of models and controllers. The first set was for spontaneously breathing and the second set for ventilated patients. All of the controllers and patient models gave satisfactory results when tested individually. Later these two sets of controllers and patient models were studied in closed-loop modes. The robustness to the sensitivity of the regression patient model was also investigated. Various tests were performed with these closed-loop situations. Results and performance of these tests are discussed in the paper.

Anesthesia↗
PubMed1993

Pilot study of an expert system adviser for controlling general anaesthesia.

RESAC (real time expert system for advice and control), has been developed to advise on the concentration of inhaled volatile anaesthetics during anaesthesia. It merges clinical information and on-line measurements using Bayesian inference and fuzzy logic. This paper describes a clinical trial in seven patients after initial development of the knowledge base and the human computer interface. Evaluation of the performance of RESAC included analysis of questionnaire responses. Anaesthetists were confident enough to follow the dosage advice given by RESAC in most of the patients.

Adult↗
PubMed1993

Towards a standardized anaesthetic state using isoflurane and morphine.

In 34 patients undergoing major surgery, the inspired isoflurane concentration was adjusted by a control system designed to maintain systolic arterial pressure at a predetermined value. An empirical rule allowed additional morphine administration if the demand of the system for isoflurane was excessive. Satisfactory control of systolic arterial pressure was achieved in 31 patients and the anaesthetic state was clinically acceptable to an independent observer; no awareness was reported and the mean recovery time was 9.6 min. In these patients, control of systolic arterial pressure produced a pattern of clinical signs recognizable as general anaesthesia.

Adult↗
PubMed1992

Control strategies for nonlinear dynamics of muscle relaxant anaesthesia.

Using modern nonlinear identification techniques, dose-response dynamics for two muscle relaxant trials have been obtained. A so-called NARMAX model has been found for Vecuronium applied to a dog, and Atracurium given to a human. With the relaxant dynamics structure thus obtained, the work proceeded to the control phase. Simple three-term PID controllers were first designed with their parameters being optimised, off-line, using the Simplex method. The non-adaptive nature of this class of controllers makes their robustness open to question when the system parameters for which they have been optimised change. Hence, adaptive controllers in the form of linear and nonlinear generalised minimum variance self-tuners, generalised predictive control and nonlinear k-step ahead predictive controllers are also considered. All of these latter control approaches are shown to be satisfactory, in terms of transient and steady-state performance.

Algorithms↗
PubMed1992

Development of an expert system advisor for anaesthetic control.

A review is given of numerous approaches which have been taken to provide automated control of depth of anaesthesia. Most of these approaches use a single indicator for anaesthetic state, and do not perform adequately for such a complex system. It is desirable, therefore, to merge a number of qualitative clinical signs and quantitative on-line measurements to provide decision-support for control of anaesthetic depth. The paper describes such an expert system called Resac (Real time Expert System for Advice and Control). Details of the knowledge representation and inference structure are given, together with the method adopted for propagating uncertainty measures, combining fuzzy information and merging quantitative and qualitative indicators. The importance of good human machine interface design is shown via the GEM-based graphics of Resac.

Anesthesiology↗
PubMed1991

Towards a standardized anaesthetic state using enflurane and morphine.

General anaesthesia was maintained in 22 patients undergoing major surgery using a proportional-plus-integral control system. The system automatically adjusted the dose of enflurane according to the systolic arterial pressure (SAP). Additional morphine was administered if the system's demand for enflurane exceeded preset limits. In 21 patients, satisfactory control of SAP was achieved and anaesthesia was clinically adequate; no awareness was reported and the mean recovery time was 6.7 min (SD 3.5 min).

Adult↗
PubMed1990

Self-organising learning control and its application to muscle relaxant anaesthesia.

The concept of a self-organising control system is attractive in biomedicine because of the imprecise nature of available physiological models. In this paper a particular strategy called a self-organising controller (SOC) originating from the work of Barron on aerospace systems is applied to the control of muscle relaxant anaesthesia. The SOC algorithm, which requires no prior knowledge of system dynamics, is described, both in single variable and multivariable format. Simulation results are presented for SOC performance on a well-established pancuronium model. Three implementations are described, being the use of a general purpose language, a SUN workstation approach, and a parallel computer transputer solution. The latter approach becomes important for multivariable control because of the computing-intensive nature of SOC. The transputer is shown to be a suitable vehicle for implementation in terms of speed and parallelism for SOC.

Algorithms↗
PubMed1989

A self-tuning Smith predictor applied to the control of blood pressure: simulation studies.

Significant time-delays occur in the response of blood pressure to drug therapy. The classical Smith predictor algorithm used to eliminate such delays is extended here to the principle of self-tuning under mis-match conditions. Two delay-free controller algorithms are investigated, being a self-tuning pole-placement and a self-tuning PID structure. Extensive simulation studies using the well-known Slate model have demonstrated the good transient performance obtained with this self-tuning Smith principle in various combinations, and under realistic variability of patient dynamics.

Algorithms↗
PubMed1989

Automatic control of neuromuscular block with atracurium.

We have developed and tested a system for providing automatic control of neuromuscular block with atracurium. The degree of neuromuscular block was monitored in the small muscles of the hand using a Datex Relaxograph, and the signal was used as the controlled variable for a proportional plus integral controller. A preloaded integral was used to shorten the period of stabilization. The system was tested in 36 patients undergoing surgery and found to produce stable block. For a target T1 of 20% of control value, the mean block was 18.7 (SD 1.3) % of baseline T1 and the mean consumption of atracurium was 5.39 (SD 1.23) micrograms kg-1 min-1. The block was sufficiently stable to act as a background for studies of pharmacological and physiological interactions with atracurium.

Adult↗
PubMed1986

Clinical automatic control of neuromuscular blockade.

A simple feedback control technique has been used to automatically deliver pancuronium to anaesthetised surgical patients. The dosage rate is automatically adjusted at 10-second intervals, according to the measured evoked, rectified, integrated electromyogram. When set to demand 80 percent blockade, in 40 patients, the controller maintained blockade at a steady mean level of 72.9 percent (consuming pancuronium at a mean rate of 0.47 microgram/kg/minute). The main clinical practical problems involved protection against electrical noise and the need to spend time setting up the equipment.

Adolescent↗
PubMed1985

Transient interactions between blood pressure, respiration and heart rate in man.

Auto regressive spectral estimation techniques have been used to follow transient interactions between mean blood pressure, respiration and heart rate. This demonstrates that these inter-relationships are variable. It is concluded that while central modulation of heart rate is the major factor in the interactions, when the heart rate is fixed, peripheral modulation of the blood pressure by respiration is clearly demonstrated.

Adult↗