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Biomedical subjects

L C Sheppard

Publications and source records attributed to L C Sheppard.

17 recordsLinked to original sources
PubMed1992

Fuzzy control of mean arterial pressure in postsurgical patients with sodium nitroprusside infusion.

We developed a fuzzy control system to provide closed-loop control of mean arterial pressure (MAP) in postsurgical patients in a cardiac surgical intensive care unit setting by regulating sodium nitroprusside (SNP) infusion. The fuzzy controller, originally expert-system-based, was analytically converted to ten nonfuzzy control algorithms, which reduced execution time dramatically. The core of the control algorithms was a nonlinear proportional-integral (PI) controller whose proportional gain and integral gain adjusted continuously according to error and rate change of error of the process output. The gains became larger when process output was far from desired setpoint and smaller when process output was close to desired setpoint, resulting in more dynamic and stable control performance than the regular PI controller, especially when a linear process with time-delay or a nonlinear process was involved. The control algorithms, encoded in C programming language, were implemented to control MAP in patients. Preliminary clinical results showed that the average percentage of time in which MAP stayed between 90% and 110% of the MAP setpoint was 89.31%, with a standard deviation of 4.96%. These were calculated based on 12 patient trials, with total trial time of 95 and 13 min.

Algorithms↗
PubMed1990

Automated administration of lidocaine for the treatment of ventricular arrhythmias.

An automated lidocaine infusion system has been developed for the treatment of ventricular arrhythmias. A drug serum concentration which is in the therapeutic range is initially achieved and maintained by an open-loop infusion regimen. The lidocaine infusion rate is then adjusted using closed-loop control to regulate the rate of premature ventricular contractions (PVC rate) at a setpoint. The major system components are a portable computer, a computer-controlled drug infusion pump, and an arrhythmia monitor which is used to measure the PVC rate. During closed-loop control, the drug infusion rate is constrained to keep the predicted serum concentration below an upper limit (ceiling concentration) so that toxic serum concentrations are avoided. The infusion rate is also constrained to keep the predicted serum concentration above a minimum value (floor concentration) to ensure the maintenance of a therapeutic serum level during closed-loop control. The system has been evaluated in initial clinical trials.

Algorithms↗
PubMed1990

Automatic control of anesthetic delivery and ventilation during surgery.

Use of a closed rebreathing circuit for anesthesia delivery offers several advantages: conservation of anesthetic agent, natural heating and humidification of inspired gases, less pollution, and improved monitoring. However, the technique requires careful control of the fresh gas and anesthetic delivery. An anesthesia delivery system has been developed which automatically controls fresh gas delivery, anesthetic delivery, and ventilation in order to regulate circuit volume, oxygen concentration, end-tidal anesthetic concentration, and end-tidal PCO2. This system makes available the advantages of closed-circuit anesthesia without encumbering the anesthesiologist with its more demanding control tasks. The system has undergone clinical testing in adult surgical patients. Maintenance of circuit volume, oxygen concentration, end-tidal anesthetic concentration, and end-tidal PCO2 was achieved by the system in all patients but the first. The anesthetic delivery controller required tuning on the first patient. No further tuning was required for any of the other patients or controllers. During abdominal surgery, the end-tidal bellows position measurement and end-tidal anesthetic concentration measurement increased in variability. The cause of the variability and its elimination are discussed in the article.

Adult↗
PubMed1990

Real-time expert-system-based fuzzy control of mean arterial pressure in pigs with sodium nitroprusside infusion.

This paper deals with real-time fuzzy control of mean arterial pressure (MAP) in pigs by regulating the infusion rate of the vasodilator drug, sodium nitroprusside (SNP). The fuzzy controller was based on the parallel firing mode of a general-purpose Fuzzy LOgic Production System shell, FLOPS [2,3,16,20]. One of the major advantages of this fuzzy control drug delivery system over other existing automatic drug delivery systems is that the fuzzy control system may be designed by using experts' knowledge and experience without any explicit mathematical models involved. Mean arterial pressure in pigs was controlled satisfactorily in real-time by the fuzzy control system. It comes to the conclusion that it may be feasible to employ this fuzzy controller in the management of mean arterial pressure of patients clinically. Also, various applications of the fuzzy controller may exist in industry and in biomedical engineering.

Animals↗
PubMed1987

Anticonvulsant medication in a mental handicap hospital: 1972-1982.

The prescription sheets for all patients in a mental handicap hospital on one day in 1972 and on the same date in 1982 were examined to identify trends in anticonvulsant medication over a 10-year period. There was a reduction in size of the hospital population associated with fewer very young and milder handicapped persons. Prescription of anticonvulsants fell slightly during the decade under study with a dramatic fall in the use of phenobarbitone, and a parallel increase in the prescription of carbamazepine. Other changes included the use of sodium valproate in a significant minority of patients and the occasional use of clonazepam in 1982, while phenytoin remained a first-rank anticonvulsant throughout the period under review. The proportions of patients on polytherapy did not change over the 10-year period, though the contribution of phenobarbitone to the combined drug regimes was significantly reduced.

Anticonvulsants↗
PubMed1985

A microcomputer based controller for neuromuscular block during surgery.

A microcomputer based control system has been developed to automatically induce and maintain neuromuscular block during surgery. The system repeatedly adjusts the infusion rate of a muscle relaxant, succinylcholine, based on the evoked, rectified, and integrated electromyogram (EMG). The system was tested in 12 patients for a 30-min infusion period with a setpoint of 80% depression of the evoked, rectified, and integrated thenar EMG. The mean time to reach the setpoint for 10 of the patients was 5.5 (+/- 1.87 SD) min and the mean time for 95% recovery after infusion was stopped was 5.4 (+/- 0.83 SD) min. Average overshoot was 9.9% of the baseline (+/- 3.1% SD), and the average time within +/- 10% of the setpoint was 22.1 min (+/- 7.26 SD). The total dose of succinylcholine for these 10 patients ranged from 1.21 to 3.77 mg/kg with a mean of 1.92 mg/kg. The other two patients were relatively insensitive to the drug and the controller was unable to bring the response to the setpoint due to a ceiling placed on infusion rate by the control algorithm.

Computers↗
PubMed1976

The application of a semiautomated postoperative care program in a community hospital: early results.

The clinical involvement of computer technology in medical center environment has been successfully utilized in the postoperative care of patients following open intracardiac operations. This report describes the initial experience in a community hospital with the adaptation and evaluation of such a system in the postoperative care of critically ill patients. The early experience with this noncomputerized system suggests the clinical usefulness of the approach, the potential increase in manpower utilization, and the greater utilization of the nursing staff in true patient care. The early results of the study do not indicate that this approach to patient care is necessarily economically feasible or technically applicable in all community hospitals.

Aged↗
PubMedDate not supplied

Automation of measurements and interventions in the systematic care of postoperative cardiac surgical patients.

Since July of 1967, a computer-based system has been employed in the observation and treatment of 8500 patients following cardiac surgical procedures. Of the 12 beds in the University of Alabama Hospital Cardiac Surgical Intensive Care Unit, 10 are equipped with biomedical instrumentation interfaced with digital computer systems. These systems perform the automatic acquisition, display, storage, retrieval, and charting of measurements; computation and evaluation of acid-base balance from manually entered blood gas data; analysis of the data for the detection and treatment of impaired cardiac performance; automatic control of blood infusion and vasodilating agents by closed-loop feedback control techniques; hourly evaluation of chest tube drainage patterns to detect excessive blood loss in the early hours following operation; and computation of the infusion rate (ml/hr) of pharmacologic agents according to a specified dosage (microgram/kg/min). Automatic control of left atrial pressure by blood infusion has been applied to 8000 patients during the past 10 years. Regulation of mean arterial pressure by computer-controlled infusion of vasodilating agents has been performed in 400 patients in the last 2 years. The use of the system has contributed to the reduction of patient time spent in the unit to 24 hours or less for the majority of the patients.

Cardiac Surgical Procedures↗