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Rehabilitation Engineering, IEEE Transactions on

Issue 2 • Date June 1998

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Displaying Results 1 - 16 of 16
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  • A strategy used by paraplegics to stand up using FES

    Page(s): 162 - 167
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    Many paraplegics can stand up if their leg extensor muscles are stimulated without feedback to the stimulator-controller. Their neurologically-intact upper bodies control the motion by exerting forces through the arms. To develop stimulator-controllers, the authors wish to understand the strategy they use. In two subjects, the authors measured the handle forces and the posture during standing up. Plotted so as to relate the handle forces to the leg joints, the results show that the upper body helps extend the knees and then the hips: a strategy the authors call quick knee-locking. This may keep the upper body forces within the limits of its strength View full abstract»

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  • Analysis of current density and related parameters in spinal cord stimulation

    Page(s): 200 - 207
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    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. At the threshold stimulus of a large dorsal column fiber, current density and charge density per pulse at the contact surface were found to be highest (1.9·105 μA/cm2 and 39.1 μC/cm2 ·p, respectively) when the contact surface was only 0.7 mm 2. When stimulating with a pulse of 500 μs, highest charge per pulse (0.92 μC/p), and the largest charge density per pulse in the dorsal columns (1.59 μC/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 View full abstract»

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  • Switching curve controller for FES-assisted standing up and sitting down

    Page(s): 167 - 171
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    A low-level, closed-loop controller for FES-assisted standing up and sitting down is described. If, for able-bodied individuals, when standing up and sitting down, the knee angular velocity is plotted against knee angle, consistent phase-plane trajectories are produced. The bang-bang controller uses a model of this trajectory as a switching curve. The design rationale for the controller was the desire to avoid injuries that might occur if knee-locking on standing up and seat-contact on sitting down are not adequately controlled. This switching curve controller (SCC) was incorporated within a hierarchical, finite state control scheme, with electrical stimulation applied bilaterally to the knee extensors. The SCC was tested in a pilot study on a female volunteer with paraplegia (T5/6 ASIA A) and evaluated against an unramped, open-loop controller (OLC). The vertical hand forces and knee angles were measured. The subject was able to achieve standing up and sitting down safely using both controllers. For standing up, the SCC was not found to offer any quantifiable advantages over the OLC and was found to increase the hand force by 8.4%. In contrast, for sitting down the SCC was found to reduce the knee angular velocities as the subject approached the seat by 27%, demonstrating a safer, softer landing View full abstract»

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  • Arm-free paraplegic standing. I. Control model synthesis and simulation

    Page(s): 125 - 138
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    This paper is the first part of the authors' 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. The knees and hips are maintained in an extended position by functional electrical stimulation (FES). The analysis of a linearized double inverted pendulum model revealed that with properly selected ankle stiffness the system can be easily stabilized. The authors developed a closed-loop double inverted pendulum model including a neural system delay, trunk muscles dynamics, body segmental dynamics and linear quadratic regulator (LQR) optimal controller. Through simulations of the closed-loop model two different strategies for disturbance rejection were explained. The authors 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, the authors 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/° suffices for arm-free standing of paraplegic subjects View full abstract»

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  • Digital signal processing algorithms for the detection of afferent nerve activity recorded from cuff electrodes

    Page(s): 172 - 181
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    Due to the very poor signal-to-noise ratios (SNR's) usually encountered with whole nerve-cuff signals, the processing method typically applied, rectification and windowed (bin)-integration (RBI), can have serious shortcomings in extracting reliable information. In order to improve detection accuracy, these signals were further analyzed using statistical signal detection algorithms based on their second and higher order spectra (HOS). A comparison with both analog and digital RBI processing suggests that the statistical methods, due to their ability to separate the signal and noise subspaces, are superior. It was determined that the noise typically encountered with nerve-cuff electrode signals is normally (Gaussian) distributed. Therefore, third-order statistics can be applied to, ideally, completely reject the noise component. When cutaneous nerve recordings from the calcaneal nerve (innervating the heel area) were used in a drop-foot correction neural prosthesis, the detection percentage and the insensitivity to algorithm parameters were increased through the use of these statistical methods as to warrant their real-time implementation, and the inherent additional processing hardware that entails View full abstract»

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  • A comparison between control methods for implanted FES hand-grasp systems

    Page(s): 208 - 218
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    Implanted neuroprostheses employing functional electrical stimulation (FES) provide grasp and release to individuals with tetraplegia. This paper describes and compares three methods of controlling the stimulated hand movement: shoulder position, wrist position and myoelectric activity from the wrist extensors. Three experienced neuroprosthesis users were evaluated with each of the control methods by performing a grasp release test (GRT). A significant improvement was found between each functional electrical stimulation (FES) method and tenodesis without FES. No significant difference in overall performance was found between the three FES methods of control. Each method of control demonstrated advantages and disadvantages which depend upon characteristics of the individual patient. Factors which must be considered are injury level, voluntary wrist strength, proximal upper limb strength, the level of cognition of the patient, hand-grasp characteristics, cosmeses, importance of using both arms, and personal preference. Due to the unique characteristics of each controller type, it is advantageous to have each type available for the FES patients to adapt the system to the needs and desires of the individual patient View full abstract»

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  • Segment velocities in normal and transtibial amputees: prosthetic design implications

    Page(s): 219 - 226
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    Dynamic elastic response foot and ankle prostheses (Seattle-Lite, Flex Foot, etc.) used by transtibial amputees feature substantial design improvements over conventional designs (SACH, Single Axis, etc.). Despite this progress, transtibial amputees continue to expend greater energy than normals. Increased residual limb EMG data and altered gait patterns suggest that impaired mobility may be the cause of overactive muscles in early stance. Prosthetic mobility was therefore quantified by measuring foot, shank and thigh velocities in nine transtibial amputees, wearing 3 different foot designs: Single Axis (SA), Seattle Lite (SL) and Flex Foot (FF). The magnitude, timing and rate of segment velocities for each prosthetic design, characterizing early stance mobility, were compared with corresponding measures in normal, nonamputee (NA) controls using Dunnett's test. Regardless of foot type, transtibial (TT) amputees walked slower than non amputee controls (63.3-65.8 m/min versus 78.5 m/min, p<0.05) and their stride length was shorter (1.21-1.26 m versus 1.41 m, p<0.01). In early stance, peak foot and shank velocities were lower (p<0.01) for both the SL and FF while only shank velocity was lower (p<0.01) with the SA compared to NA controls. Significant delays in the timing of early stance events such as peak shank velocity, peak ankle plantarflexion and peak knee flexion compromised shank and knee stability in TT amputees. Foot and shank mobility was uncontrolled with the SA design while ankle mobility was restricted by the FF and SL feet. In NA controls on the other hand, appropriate timing and rate of segment velocity changes preserved dynamic stability and forward progression in early stance. This was evidenced by rapid decreases in foot and shank velocity as the thigh velocity increased during weight acceptance. Future prosthetic designs should provide TT amputees with improved ankle mobility that attempt to capture the dynamic characteristics of a normal articulation between the foot and shank segments during the early stance weight acceptance period View full abstract»

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  • Arm-free paraplegic standing. II. Experimental results

    Page(s): 139 - 150
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    For pt. I see ibid., vol. 6, no. 2, p. 125-38 (1998). In pt. I, the authors proposed an approach for restoring unsupported standing to thoracic-level paraplegics. The theoretical analysis and simulation of an underactuated double inverted pendulum, representing the standing subject, showed that arm-free standing might be achieved. Here in pt. II, the authors present the mechanical apparatus which they used in their experiments and experimental results from tests of the balance-control strategy. They demonstrate that an intact and a paraplegic subject could perform quiet standing with the ankle stiffness set to 8 Nm/° or even less (the intact subject). Both were also able to recover from disturbances, imposed by the artificial ankle joint of the apparatus. Introducing cognitive auditory feedback greatly improved the standing abilities of both subjects View full abstract»

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  • Patient-driven control of FES-supported standing up: a simulation study

    Page(s): 113 - 124
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    To control movements aided by functional electrical stimulation (FES) in paraplegic patients, stimulation of the paralyzed lower limbs might be adjusted in response to voluntary upper body effort. Recently, Donaldson and Yu (ibid., vol. 4, p. 280-4, 1996) proposed a theoretical approach, called “control by handle reactions of leg muscle stimulation” (CHRELMS), in which stimulation of the lower limbs depends on upper body effort, i.e., body posture and recorded hand reactions, and is aimed to minimize arm forces during standing up and standing. An alternative strategy is presented in this paper, which accounts for voluntary upper body effort as well, but does not require estimation of hand reactions. The objective of this study is to test both strategies by applying them to a generic two-dimensional (2-D) neuromusculoskeletal model. The model takes into account the major properties of muscle and segmental dynamics during FES-supported standing up movements of a paraplegic patient. In comparison to standing up without FES-support, both closed-loop strategies yield satisfying standing-up movements although no reference information (e.g., a desired trajectory) is required. Arm forces can be significantly reduced. Using the model to optimize the controller, time-consuming and strenuous trial-and-error experimentation could be avoided. However, final experimental studies are planned to verify the presented strategies View full abstract»

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  • Stretch reflex sensitivity: effects of postural and muscle length changes

    Page(s): 182 - 189
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    In this study, a combination of clinical evaluation, laboratory testing, and model simulation of spasticity is performed under various postural conditions to investigate the changes in the sensitivity and specific mechanisms of spasticity. Fifty-nine multiple sclerosis patients participated in the study and received spasticity evaluation based on both the Ashworth scale and the pendulum test. Spasticity was found to increase in the pendulum test when the subjects were tested in a supine posture, compared to when they were sitting. Three patterns of stretch reflex response were seen for similar leg swing trajectories. While it was clear that the increased stretch of rectus femoris in the supine posture contributed to the increased spasticity, the results of modeling showed that other more complex factors were also involved. The supraspinal descending modulation associated with postural control may play a more dominant role in the severity of spasticity. The results suggest that the biomechanical test of spasticity should be performed for several different postures or ranges of movement with muscle activities monitored simultaneously, so that the effect of various factors can be examined. The work also indicates that a neuromusculoskeletal model with detailed muscle dynamics and stretch reflex loops is a valuable tool for investigating the neural mechanisms of spasticity View full abstract»

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  • Control Of FES-supported Standing

    Page(s): 0_1
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    First Page of the Article
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  • Functional neuromuscular stimulation for combined control of elbow extension and hand grasp in C5 and C6 quadriplegics

    Page(s): 190 - 199
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    Spinal cord injury sustained at the C5/C6 level leaves an individual without voluntary control of the muscles of the forearm, hand, or of the elbow extensors. The objective of this research project was to integrate functional neuromuscular stimulation (FNS) control of elbow extension with a previously developed system that provides hand grasp in order to increase the working volume in space in which users can perform functional tasks. Elbow extension control was achieved by detecting the position of the arm in space and determining the magnitude of the gravitational moment acting to oppose extension. An accelerometer was used as the command control source, and this sensor was placed over the ulna near the elbow joint to detect static (gravitational) acceleration, and therefore the gravitational moment acting about the elbow joint. This value determined the level of electrical stimulation required to activate the triceps muscles to full extension against these forces. Combined FNS control of elbow extension and hand grasp was implemented in two quadriplegic subjects. Both subjects were able to reach and grasp objects at locations in space which were unattainable without triceps activation View full abstract»

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  • Computer simulation of FES standing up in paraplegia: a self-adaptive fuzzy controller with reinforcement learning

    Page(s): 151 - 161
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    Using computer simulation, the theoretical feasibility of functional electrical stimulation (FES) assisted standing up is demonstrated using a closed-loop self-adaptive fuzzy logic controller based on reinforcement machine learning (FLC-RL). The control goal was to minimize upper limb forces and the terminal velocity of the knee joint. The reinforcement learning (RL) technique was extended to multicontroller problems in continuous state and action spaces. The validated algorithms were used to synthesize FES controllers for the knee and hip joints in simulated paraplegic standing up. The FLC-RL controller was able to achieve the maneuver with only 22% of the upper limb force required to stand-up without FES and to simultaneously reduce the terminal velocity of the knee joint close to zero. The FLC-RL controller demonstrated, as expected, the closed loop fuzzy logic control and on-line self-adaptation capability of the RL was able to accommodate for simulated disturbances due to voluntary arm forces, FES induced muscle fatigue and anthropometric differences between individuals. A method of incorporating a priori heuristic rule based knowledge is described that could reduce the number of the learning trials required to establish a usable control strategy. The authors also discuss how such heuristics may also be incorporated into the initial FLC-RL controller to ensure safe operation from the onset View full abstract»

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  • Integrated analyzer and classifier of glottographic signals

    Page(s): 227 - 234
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    Electroglottography (EGG) and photoglottography (PGG) are two plausible methods to study voice production for monitoring the patterns of laryngeal vibrations. It has been suggested that measures such as open quotient and speed quotient calculated from glottographic signals can provide useful information regarding pathological phonation. In this paper, an integrated analyzer and classifier of glottographic signals was implemented. The system makes it possible to calculate the measures from digitized EGG and PGG signals automatically in order to examine vocal fold abnormality. The system developed several techniques to extract features from glottographic signals and proposed a statistical classification method that can possibly aid the diagnosis process. To check the reliability of the system, a training set and a test set of glottographic signals from normal people and patients with recurrent/superior laryngeal paralysis were analyzed and classified by the system. The results showed that the system is a useful tool for quantitative study of phonatory pathophysiology and can be used by the examiner who is interested in the clinical examination of glottographic signals. Moreover, glottographic techniques may have some clinical applications in the quantitative documentation of phonatory function in patients with voice disorders but requires further evaluation before clinical application View full abstract»

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  • Hearing aid electromagnetic interference from digital wireless telephones

    Page(s): 235 - 239
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    Several in-the-ear (ITE) and behind-the-ear (BTE) hearing aids were tested for audible interference at various distances from five types of digital wireless telephones. The interference which takes the form of a buzzing and a static sound was quantified using a calibrated system including a frequency analyzer and a pressure field microphone. The output of the each hearing aid was coupled to the microphone via Tygon tubing and a standard 2 cc coupler. The highest interference-induced sound pressure level (SPL), 122.5 dB, was measured from a BTE hearing aid placed within 2 cm of a transmitting Global System for Mobile Communications (GSM) phone. In this case, interference was detected up to a separation distance of almost 3 m. While all phones tested produced a similar interference level within 2 cm of this hearing aid, interference SPL from the code division multiple access (CDMA)-based system decreased more rapidly with distance than the time division multiple access (TDMA)-based phones tested View full abstract»

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Aims & Scope

This Transaction ceased publication in 2000. The current retitled publication is IEEE Transactions on Neural Systems and Rehabiliation Engineering.

Full Aims & Scope