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Biomedical subjects

G J Derbyshire

Publications and source records attributed to G J Derbyshire.

5 recordsLinked to original sources
PubMed1997

The use of a PID controller to model vecuronium pharmacokinetics and pharmacodynamics during liver transplantation. Proportional-integral-derivative.

A four-phase proportional-integral-derivative (PID) controller was evaluated under the extremely unstable conditions of liver transplantation. Vecuronium was delivered to achieve 80%-90% neuromuscular blockade as measured by electromyogram (EMG). The first two controller phases delivered boluses and a constant infusion calculated to rapidly achieve setpoint, followed by a proportional-derivative (PD) phase at 35% from setpoint, and PID within 10% of the setpoint. During liver transplantation, the sources of system instability included large blood losses, temperature changes, and loss of hepatic drug metabolism during removal and replacement. During prolonged surgery, and when blood losses were not severe, the EMG remained within 10% of setpoint. Controller performance was more variable during system instability. Plasma sampling and two-compartment modelling of the infusion and response with a weighting factor for blood loss allowed estimation of the sources and degree of instability for improved design of future controllers.

Adolescent↗
PubMed1991

Closed-loop infusion of atracurium with four different anesthetic techniques.

A new proportional-integral-derivative (PID) controller for the automated closed-loop delivery of atracurium was tested in 32 patients. Groups of 8 patients received halothane, enflurane, isoflurane, or N2O/morphine anesthesia. After induction of anesthesia with sodium thiopental 3-5 mg.kg-1, a bolus of atracurium 0.2 mg.kg-1 was delivered by the controller; this was followed by an infusion calculated by the controller to maintain the electromyogram (EMG) at a setpoint of 90% neuromuscular blockade. The average overshoot for the controller was 10.1% and the mean steady-state error 3.0%. The mean infusion rates for atracurium to maintain 90% blockade were calculated for each anesthetic group, with the inhalation anesthetics at 1 MAC. Infusion rates for N2O/morphine, halothane 0.8%, enflurane 1.7%, and isoflurane 1.4% at 90% blockade were 5.7 +/- 0.6, 4.9 +/- 0.3, 3.5 +/- 0.3, and 4.1 +/- 0.5 micrograms.kg-1.min-1, respectively (mean +/- SE). The infusion rate for atracurium at 90% blockade under N2O/morphine anesthesia was in general agreement with published values. The other infusion rates at 90% blockade have not been reported previously, but correspond to the known potencies of these inhalation anesthetics for augmentation of neuromuscular blockade. This controller performed well in comparison to previously developed controllers, and in addition was used as a research tool for rapid estimation of infusion rates.

Adult↗
PubMed1990

Thermally induced optical property changes in myocardium at 1.06 microns.

Light in the visible and near-infrared region is diffusely scattered in tissues by macromolecules. It was therefore hypothesized that tissue coagulation caused by high-power continuous wave laser irradiation might significantly alter tissue optical properties, resulting in a redistribution of laser energy during the laser ablation process. Infrared transmittance studies confirmed the hypothesis by demonstrating an irreversible decrease in light transmittance (45%) during heating of a 0.75 mm thick slice of tissue. Absorption and scattering coefficients were then determined from transmittance and reflectance measurements on thin slices of raw and coagulated myocardium irradiated with a Nd:YAG laser (1.06 microns). The scattering coefficient was found to increase fourfold (0.427 mm-1----1.74 mm-1) during tissue coagulation, while the absorption coefficient remained relatively unchanged (0.044 mm-1----0.051 mm-1). Calculations indicate that the coagulation-induced changes in tissue optical properties substantially increase surface back-scattering and reduce tissue penetration.

Animals↗