IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Nov 1992
The activating function for magnetic stimulation derived from a three-dimensional volume conductor model.
A three-dimensional volume conductor model of magnetic stimulation is proposed that relates transmembrane potential of an axon to the induced electric field in a uniform volume conductor. This model validates assumptions used to derive a one-dimensional cable model of magnetic stimulation (Roth & Basser, IEEE Trans. ⋯ Eng., vol. 37, pp. 588-597, 1990) of unmyelinated axons. The three-dimensional volume conductor model reduces to this one-dimensional cable equation forced by the activating function, -delta EzA/delta z.
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This paper describes the design of an adaptive closed-circuit anesthesia controller based on a multiplexed mass spectrometer system. The controller deals with measurement deterioration caused by measurement delay and rise time through a long catheter as well as long sampling times due to the multiplexed measurements. ⋯ A multiple-step-ahead predictive control algorithm is used to calculate intermediate control inputs between sampling intervals. Simulations are used to validate the designed controller.
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IEEE Trans Biomed Eng · Oct 1992
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 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.
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IEEE Trans Biomed Eng · Sep 1992
Recruitment of dorsal column fibers in spinal cord stimulation: influence of collateral branching.
An electrical network model of myelinated dorsal column nerve fibers is presented. The effect of electrical stimulation was investigated using both a homogeneous volume conductor and a more realistic model of the spinal cord. ⋯ It was found that transmembrane potentials, due to external monopolar stimulation, at the node at which a collateral is attached, is significantly influenced by the presence of the collateral. It is concluded that both excitation threshold and blocking threshold of dorsal column fibers are decreased up to 50% compared to unbranched fibers.
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IEEE Trans Biomed Eng · Sep 1992
Comparative StudyAccuracy of drug infusion pumps under computer control.
Prototype systems implementing algorithms for automated drug infusions are typically constructed by coupling a microcomputer to a drug infusion pump through a serial communications interface. Infusion rates demanded of the infusion pump in many computed-controlled drug delivery applications are made to change at intervals much shorter than those encountered under routine clinical use. Because the ability of infusion pumps to maintain accurate flow rates during high frequency rate changes has not been documented, the purpose of this study was to validate the volumetric accuracy of three commercially available infusion pumps operating in a demanding computer-controlled application. ⋯ Accuracy of the infusion devices was determined gravimetrically. At all measurement times, each of the infusion pumps was accurate to within approximately +/- 5% of the expected volumetric output under each of the infusion rate intervals tested. Flow rate accuracy of +/- 5% is equal to the nominal expected accuracy of these infusion pumps in conventional clinical use.