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When stimulating muscles, EMG signals recorded in neighboring muscles can be contaminated by stimulus artifacts, and artifact deletion is necessary. We have devised a digital technique for removing stimulus artifacts from rectified EMG recordings in muscles which lie close to a stimulated muscle. This artifact deletion method replaces the rectified EMG during the artifact interval with an estimate of the rectified EMG. Our research requires detection of very small changes in EMG levels. Therefore, the artifact deletion technique described in this paper was designed to leave less than 10 microV of artifact in the rectified EMG post-processing. This technique relies on being able to estimate the artifact duration. Since stimulated muscles have M-waves that can overlap with artifacts, our technique is only appropriate for removing artifacts in muscles which are not being stimulated. Unlike other artifact elimination techniques, our technique does not change the mean value of the rectified EMG, regardless of artifact width. In addition, it provides a more accurate estimate of the rectified EMG during the artifact interval as opposed to sample-and-hold techniques.

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We investigated the interaction of smooth ocular pursuit (SP) and the vestibulo-ocular reflex (VOR) during horizontal, combined eye-head tracking (CEHT) in patients with abnormalities of either the VOR or SP movements. Our strategy was to apply transient stimuli that capitalized on the different latencies to onset of SP and the VOR. During CEHT of a target moving at 15 deg/sec, normal subjects and patients with VOR deficits all tracked the target with a gain close to 1.0. When the heads of normal subjects were suddenly and unexpectedly braked to a halt during CEHT, the eye promptly began to move in the orbit to track the target, but eye-in-orbit velocity transiently fell to about 60-70% of target velocity. In patients with deficient labyrinthine function, following the onset of the head brake, eye movements to track the target were absent, and SP movements were not generated until about 100 msec later. In patients with deficient SP, CEHT was superior to SP tracking with the head stationary; after the onset of the head brake, tracking eye movements were initiated promptly, but eye velocity was less than 50% of target velocity and increased only slightly thereafter. These results indicate that at least two mechanisms operate to overcome the VOR and allow gaze to track the target during CEHT: (1) the SP system provides a signal to cancel a normally-operating VOR (this cancellation signal is not needed by labyrinthine-deficient patients who have no VOR to cancel), and (2) a reduction of the gain of the VOR is achieved, an ability that is preserved even in patients with cerebral lesions that impair SP.

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Functional electrical stimulation can be used to provide hand opening in hemiplegics with spastic finger flexor muscles through stimulation of the extensor digitorum communis (EDC) muscle and the ulnar nerve. Stimulation of the finger extensor muscles in both hemiplegics and nonneurologically impaired individuals does not appear to cause significant reciprocal inhibition of finger flexor muscles. Thus stimulation of the EDC and ulnar nerve may not decrease finger flexor spasticity in the hemiplegic subjects, yet functional hand opening can still be obtained through a direct mechanical effect of the extensor stimulation.

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1. We used a modeling approach to test the hypothesis that, in humans, the smooth pursuit (SP) system provides the primary signal for cancelling the vestibuloocular reflex (VOR) during combined eye-head tracking (CEHT) of a target moving smoothly in the horizontal plane. Separate models for SP and the VOR were developed. The optimal values of parameters of the two models were calculated using measured responses of four subjects to trials of SP and the visually enhanced VOR. After optimal parameter values were specified, each model generated waveforms that accurately reflected the subjects' responses to SP and vestibular stimuli. The models were then combined into a CEHT model wherein the final eye movement command signal was generated as the linear summation of the signals from the SP and VOR pathways. 2. The SP-VOR superposition hypothesis was tested using two types of CEHT stimuli, both of which involved passive rotation of subjects in a vestibular chair. The first stimulus consisted of a "chair brake" or sudden stop of the subject's head during CEHT; the visual target continued to move. The second stimulus consisted of a sudden change from the visually enhanced VOR to CEHT ("delayed target onset" paradigm); as the vestibular chair rotated past the angular position of the stationary visual stimulus, the latter started to move in synchrony with the chair. Data collected during experiments that employed these stimuli were compared quantitatively with predictions made by the CEHT model. 3. During CEHT, when the chair was suddenly and unexpectedly stopped, the eye promptly began to move in the orbit to track the moving target. Initially, gaze velocity did not completely match target velocity, however; this finally occurred approximately 100 ms after the brake onset. The model did predict the prompt onset of eye-in-orbit motion after the brake, but it did not predict that gaze velocity would initially be only approximately 70% of target velocity. One possible explanation for this discrepancy is that VOR gain can be dynamically modulated and, during sustained CEHT, it may assume a lower value. Consequently, during CEHT, a smaller-amplitude SP signal would be needed to cancel the lower-gain VOR. This reduction of the SP signal could account for the attenuated tracking response observed immediately after the brake. We found evidence for the dynamic modulation of VOR gain by noting differences in responses to the onset and offset of head rotation in trials of the visually enhanced VOR.(ABSTRACT TRUNCATED AT 400 WORDS)

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Functional electrical stimulation (FES) has been used for increasing muscle strength, decreasing spasticity, and controlling movement of limbs for many years. Most of this work, however, has been done in a research setting. Over the past decade, FES has moved slowly from the laboratory to the clinical world through feasibility studies in groups of patients with spinal cord injuries and strokes. Electrical stimulation has been shown to decrease spastic tone both during and after the stimulation, allowing for better limb positioning, decrease in contracture formation, and in some cases, improvement of voluntary movement. Electrical stimulation as a motor prosthesis is now being provided to small groups of spinal cord-injured patients (primarily C4, C5 and C6 levels) to assist with hand positioning and to produce hand grasp. In these settings, patients have attained greater independence in activities of daily living and in work-related tasks. Distribution of this technology to multiple centers is continuing through a technology transfer program.

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A model of the human carotid artery bifurcation has been constructed and tested under mean physiologic flow conditions (fluid viscosity = 0.035 poise; mean Re inlet = 400; unconstricted flow split = 70:30, internal carotid artery:external carotid artery). Smooth, axisymmetric constrictor plugs with 0, 20, 40, 60, and 80% diameter reduction are placed in the simulated proximal internal carotid artery to provide a range of flow conditions similar to those found clinically. Axial velocity measurements are made at sites +/- 0.625 radius within the lumen of the tube at distances of 0, 1, 3, 5 and 10 diameters downstream of the constrictor throat using H2 bubble markers and a 7.5 MHz ultrasound pulse Doppler. Measurement of mean, mode -3 dB down high and low and -9 dB down high and low velocities are made from selected fast-Fourier transform (FFT) spectra. The flow field downstream of the 0% diameter reduction is entirely laminar, exhibiting a peak skewed toward the flow divider along the entire 10 diameters downstream and having a consistently narrow bandwidth. Obstruction of the flow channel produces increased axial velocity at the constrictor (20%), an oscillatory jet extending approximately 5 diameters downstream (40%), a transitional jet extending approximately 5 diameters downstream (60%) and a turbulent jet extending approximately 3 diameters downstream (80%). Velocity bandwidth (both -3 dB and -9 dB) increases with degree of constriction and low velocity flow patterns exist between the center line and both tube walls. Presence of constriction produces characteristic downstream flow patterns which are distinctive for each degree of diameter reduction.

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A new versatile apparatus for investigating the neuromusculoskeletal dynamics of the upper limb, termed the Programmable Limb Testing System (PLTS) has been designed, built, and tested. The planning, construction, and operation of this system are described in this paper. Results are presented from a limited set of experiments, measuring intrinsic muscular and reflex-mediated stiffnesses of the triceps brachii, which exhibit the system's performance and some of its capabilities.

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