IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Aug 2001
Modeling and closed-loop control of hypnosis by means of bispectral index (BIS) with isoflurane.
A model-based closed-loop control system is presented to regulate hypnosis with the volatile anesthetic isoflurane. Hypnosis is assessed by means of the bispectral index (BIS), a processed parameter derived from the electroencephalogram. Isoflurane is administered through a closed-circuit respiratory system. ⋯ Anti-windup measures protect against performance degradation in the event of saturation of the input signal. Fault detection schemes in the controller cope with BIS and expired concentration measurement artifacts. The results of clinical studies on humans are presented.
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This paper discusses the single-unit recording characteristics of microelectrode arrays containing on-chip signal processing circuitry. Probes buffered using on-chip unity-gain operational amplifiers provide an output resistance of 200 ohm with an input-referred noise of 11-muV root-mean-square (rms) (100 Hz-10 kHz). ⋯ Low-noise in vivo recordings with a multiplexed probe have been demonstrated for the first time using an external asymmetrical clock running at 200 kHz. The multiplexed system adds less than 8-muV rms of noise to the recorded signals, suppressing the 5-V clock transitions to less than 2 ppm.
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IEEE Trans Biomed Eng · Jun 2001
Finite-element analysis of aortic valve-sparing: influence of graft shape and stiffness.
Aortic valve incompetence due to aortic root dilation may be surgically corrected by resuspension of the native valve within a vascular graft. This study was designed to examine the effect of graft shape and material properties on aortic valve function, using a three-dimensional finite-element model of the human aortic valve and root. First, the normal root elements in the model were replaced with graft elements, in either a cylindrical or a "pseudosinus" shape. ⋯ Regarding material properties, the polyurethane models demonstrated valve stress, strain, and coaptation values closest to normal, for either root shape. Graft shape had a greater effect on the simulated valve function than did the material property of the graft. Optimizing the shape and material design of the graft may result in improved longevity of the spared valve if a normal environment is restored.
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IEEE Trans Biomed Eng · Jun 2001
A novel approach for precise simulation of the EMG signal detected by surface electrodes.
We propose a new electromyogram generation and detection model. The volume conductor is described as a nonhomogeneous (layered) and anisotropic medium constituted by muscle, fat and skin tissues. The surface potential detected in space domain is obtained from the application of a two-dimensional spatial filter to the input current density source. ⋯ Computation of the signal in space domain is performed by applying the Radon transform; this permits to draw considerations about spectral dips and clear misunderstandings in previous theoretical derivations. The effects of generation and extinction of the action potentials at the fiber end plate and at the tendons are included by modeling the source current, without any approximation of its shape, as a function of space and time and by using again the Radon transform. The approach, based on the separation of the temporal and spatial properties of the muscle fiber action potential and of the volume conductor, includes the capacitive tissue properties.
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IEEE Trans Biomed Eng · Apr 2001
The effects of interpulse interval on stochastic properties of electrical stimulation: models and measurements.
It is known that some cochlear implant users have improved speech perception using higher rates of interleaved pulsatile stimulation. There are, however, significant limitations on their performance presumably due in part to temporal and spatial interactions. To address these limitations, we have examined refractory characteristics of the auditory nerve using experimental animal models and computational simulations. ⋯ Although it is not fully understood how the electrically evoked compound action potential (EAP) data are related to single fiber data, the RS of single fibers is a partial contributor [19]. We have measured the EAP using a monopolar intracochlear stimulating electrode and a recording electrode placed directly on the nerve and have observed changes in slope of EAP growth functions consistent with the theoretical RS values. These results have significant implications for speech coding in a cochlear implant since they suggest an increased membrane noise for pulse trains of specific rates.