IEEE transactions on rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society
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IEEE Trans Rehabil Eng · Jun 1998
Analysis of current density and related parameters in spinal cord stimulation.
A volume conductor model of the spinal cord and surrounding anatomical structures is used to calculate current (and current density) charge per pulse, and maximum charge density per pulse at the contact surface of the electrode in the dorsal epidural space, in the dorsal columns of the spinal cord and in the dorsal roots. The effects of various contact configurations (mono-, bi-, and tripole), contact area and spacing, pulsewidth and distance between contacts and spinal cord on these electrical parameters were investigated under conditions similar to those in clinical spinal cord stimulation. ⋯ When stimulating with a pulse of 500 microseconds, highest charge per pulse (0.92 microC/p), and the largest charge density per pulse in the dorsal columns (1.59 microC/cm2. p) occurred. It is concluded that of all stimulation parameters that can be selected freely, only pulsewidth affects the charge and charge density per pulse in the nervous tissue, whereas both pulsewidth and contact area strongly affect these parameters in the nonnervous tissue neighboring the electrode contacts.
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IEEE Trans Rehabil Eng · Jun 1998
Arm-free paraplegic standing--Part I: Control model synthesis and simulation.
The following paper is the first part of our investigation into the feasibility of arm-free paraplegic standing. A novel control strategy for unsupported paraplegic standing which utilizes the residual sensory and motor abilities of the thoracic spinal cord injured subjects is proposed. The strategy is based on voluntary and reflex activity of the paraplegic person's upper body and artificially controlled stiffness in the ankles. ⋯ We investigated the capability of the closed-loop model to reject disturbances, imposed at the ankle joint (in anterior and posterior directions) for various stiffness levels and neural system delays in the presence of biomechanical constraints. By limiting permissible excursions of the center of pressure, we found out that the length of the foot is the most important constraint, while the strength of the trunk muscles is not of major importance for successful balancing. An ankle stiffness of approximately 10 Nm/degree suffices for arm-free standing of paraplegic subjects.
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IEEE Trans Rehabil Eng · Mar 1997
A slowly penetrating interfascicular nerve electrode for selective activation of peripheral nerves.
To meet the future needs of functional electrical stimulation (FES) applications, peripheral nerve electrodes must be able to safely, selectively, and independently stimulate small subpopulations of the axons within a common nerve trunk. A new electrode has been designed to place contacts outside of the perineurium, but within the epineurium of the nerve. This slowly penetrating interfascicular nerve electrode (SPINE) combines the safety and simplicity of extraneural cuff electrodes with the intimate interface of intrafascicular wire and probe electrodes. ⋯ Quantification of stimulation results demonstrate interfascicular stimulation is functionally different than extraneural stimulation in 32 of 38 trials. In 19 of 28 trials, interfascicular stimulation is functionally selective based on depth of penetration and 52 of 58 trials demonstrate selectivity based on the side of the penetrating element. Third, tissue sections show that the SPINE electrode penetrates into the nerve within 24 h without evidence of edema or damage to the perineurium.
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IEEE Trans Rehabil Eng · Mar 1997
Recruitment characteristics of nerve fascicles stimulated by a multigroove electrode.
The recruitment characteristics of fascicle-selective nerve stimulation by a multigroove electrode have been investigated both theoretically and in acute experiments. A three-dimensional (3-D) volume conductor model of fascicles in a multigroove device and a model of myelinated nerve fiber stimulation were used to calculate threshold stimuli of nerve fibers in these fascicles. After their exposition, fascicles from rat sciatic nerve were positioned in different grooves of appropriate sizes and stimulated separately. ⋯ Moreover, simulations predict that the slopes of recruitment curves are smaller and inverse recruitment order is less pronounced. Simulations also showed that a small contact is preferable to a large on, because a small contact gives a slightly smaller slope of the recruitment curve. Both experimentally and theoretically a significantly smaller slope of recruitment curves was obtained by stimulation with a cathode and an anode at opposite sides of the fascicle, driven by two current sources giving simultaneous pulses with different, but linearly dependent amplitudes.
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IEEE Trans Rehabil Eng · Mar 1997
Randomized Controlled Trial Clinical TrialElectrical stimulation-induced contraction to reduce blood stasis during arthroplasty.
Deep venous thrombosis and subsequent pulmonary embolism due to venous pooling/stasis commonly occur in patients during hip and/or knee arthroplasty (i.e., replacement). This problem may be alleviated by using techniques to promote lower limb blood flow. Electrical stimulation-induced contractions have been shown to activate the skeletal muscle pump, promote limb blood flow, and may be effective for reducing venous pooling/stasis and edema. ⋯ The data suggest that continuous electrical stimulation-induced contractions could improve lower leg circulation by eliciting the physiologic muscle pump. This will lead to improved venous circulation and reduction of blood stasis during total hip and/or knee surgery. This technique may offer greater protection against DVT and PE during surgery than the commonly used sequential compression device.