Control of posture with FES systems

One of the major obstacles in restoration of functional FES supported standing in paraplegia is the lack of knowledge of a suitable control strategy. The main issue is how to integrate the purposeful actions of the non-paralysed upper body when interacting with the environment while standing, and the actions of the artificial FES control system supporting the paralyzed lower extremities. In this paper we provide a review of our approach to solving this question, which focuses on three inter-related areas: investigations of the basic mechanisms of functional postural responses in neurologically intact subjects; re-training of the residual sensory-motor activities of the upper body in paralyzed individuals; and development of closed-loop FES control systems for support of the paralyzed joints

New results in feedback control of unsupported standing in paraplegia

The aim of this study was to implement a new approach to feedback control of unsupported standing and to evaluate it in tests with an intact and a paraplegic subject. In our setup, all joints above the ankles are braced and stabilizing torque at the ankle is generated by electrical stimulation of the plantarflexor muscles. A previous study showed that short periods of unsupported standing with a paraplegic subject could be achieved. In order to improve consistency and reliability and to prolong the duration of standing, we have implemented several modifications to the control strategy. These include a simplified control structure and a different controller design method. While the reliability of standing is mainly limited by the muscle characteristics such as reduced strength and progressive fatigue, the results presented here show that the new strategy allows much longer periods (up to several minutes) of unsupported standing in paraplegia

A model-based approach to stabilizing crutch supported paraplegic standing by artifical hip joint stiffness

The prerequisites for stable crutch supported standing were analyzed in this paper. For this purpose, a biomechanical model of crutch supported paraplegic stance was developed assuming the patient was standing with extended knees. When using crutches during stance, the crutches will put a position constraint on the shoulder, thus reducing the number of degrees of freedom. Additional hip-joint stiffness was applied to stabilize the hip joint and, therefore, to stabilize stance. The required hip-joint stiffness for changing crutch placement and hip-joint offset angle was studied under static and dynamic conditions. Modeling results indicate that, by using additional hip-joint stiffness, stable crutch supported paraplegic standing can be achieved, both under static as well as dynamic situations. The static equilibrium postures and the stability under perturbations were calculated to be dependent on crutch placement and stiffness applied. However, postures in which the hip joint was in extension (C postures) appeared to the most stable postures. Applying at least 60 N /spl middot/ m/rad hip-joint stiffness gave stable equilibrium postures in all cases. Choosing appropriate hip-joint offset angles, the static equilibrium postures changed to more erect postures, without causing instability or excessive arm forces to occur

Paraplegic standing supported by FES-controlled ankle stiffness

The objective of this paper was to investigate whether a paraplegic subject-is able to maintain balance during standing by means of voluntary and reflex activity of the upper body while being supported by closed loop controlled ankle stiffness using FES. The knees and hips of the subject were held in extended positions by a mechanical apparatus, which restricted movement to the sagittal plane. The subject underwent several training sessions where the appropriate level of stiffness around the ankles was maintained by the mechanical apparatus. This enabled the subject to learn how to use the upper body for. balancing. After the subject gained adequate skills closed-loop FES was employed to regulate ankle stiffness, replacing the stiffness provided by the apparatus. A method to control antagonist muscle moment was implemented. In subsequent standing sessions, the subject had no difficulties in maintaining balance. When the FES, support was withheld, the ability to balance was lost

Design of feedback controllers for paraplegic standing

The development, implementation and experimental evaluation of feedback systems for the control of the upright posture of paraplegic persons in standing is described. While the subject stands in a special apparatus, stabilising torque at the ankle joint is generated by electrical stimulation of the paralysed calf muscles of both legs using surface electrodes. This allows the subject to stand without the need to hold on to external supports for stability- this is termed 'unsupported standing'. Sensors in the apparatus allow independent measurement of left and right ankle moments together with measurement of the inclination angle. A nested loop structure for control of standing is implemented, where a high-bandwidth inner loop provides control of the ankle moments, while the angle controller in the outer loop regulates the inclination angle. A number of important modifications to a control strategy which was previously tested with both neurologically intact and paraplegic subjects are presented. The new strategy is described, and an experimental evaluation with intact subjects is reported. The experimental results show that the control system for unsupported standing performs reliably, and according to the design formulation. There aa-e a number of design choices, appropriate to different situations, and the practical effect of each is clear. This allows easy 'tuning' during an experimental session. This is important since the complete design procedure, from muscle dynamics identification to control design, has to be carried out as quickly as possible while the subject is standing in the apparatus. A number of recommendations are made regarding the preferred design choices for control of unsupported standing

Feedback control of unsupported standing in paraplegia. Part II: experimental results

For pt. I see ibid., vol. 5, no. 4, p. 331-40 (1997). This is the second of a pair of papers which describe an investigation into the feasibility of providing artificial balance to paraplegics using electrical stimulation of the paralyzed muscles. By bracing the body above the shanks, only stimulation of the plantar flexors is necessary. This arrangement prevents any influence from the intact neuromuscular system above the spinal cord lesion. Here, the authors present experimental results from intact and paraplegic subjects

Low-level finite state control of knee joint in paraplegic standing

Low-level finite state (locked-unlocked) control is compared with open-loop stimulation of the knee extensor muscles in functional electrical stimulation (FES) induced paraplegic standing. The parameters were: duration of standing, relative torque loss in knee extensor muscles, knee angle stability, average stimulus output and average arm effort during standing. To investigate the impact of external mechanical conditions on controller performance, experiments were performed both under the condition of a freely moving ankle joint and of a mechanically stabilized ankle joint. Finite state control resulted in a 2.5 to 12 times increase of standing duration or in a 1.5 to 5 times decrease of relative torque loss in comparison with open-loop stimulation. Finite state control induced a limit cycle oscillation in the knee joint. Average maximum knee flexion was 6.2° without ankle bracing, and half that value with ankle bracing. Average arm support was 13.9 and 7.5% of the body weight without and with ankle bracing respectively

The influence of the reciprocal hip joint link in the advanced reciprocating gait orthosis on standing performance in paraplegia

The effect of reciprocally linking the hip hinges of a hip-knee-ankle-foot orthosis on standing performance was studied in a comparative trial of the Advanced Reciprocating Gait Orthosis (ARGO) and an ARGO in which the Bowden cable was removed (A_GO). Six male subjects with spinal cord injury (SCI) at T4 to T12 level participated in the study, which was conducted using a single case experimental design. Standing balance, the ability to handle balance disturbances (standing stability), and the performance of a functional hand task during standing were assessed in both orthosis configurations in the order A_GO-ARGO-A_GO-ARGO. No significant differences with respect to standing performance were found for the two orthosis configurations. However, the results indicate that the crutch force needed for maintaining balance during various tasks, especially for quiet standing with two crutches, may be much higher in the orthosis without Bowden cable. Therefore, it is very likely that the reciprocal hip joint link in the ARGO provides a substantial and clinically relevant reduction of upper body effort required for standing under functional conditions

The Use of Functional Electrical Stimulation (FES) to Produce Functional Movement in Individuals with Paraplegia

Spinal cord injury (SCI) affects approximately 7600 to 11000 people per year, and alters every aspect of the individuals\u27 lives. SCI primarily affects young Caucasian adults. The majority are between 16 to 30 years old, with the average age being 19. Motor vehicle accidents account for 35% to 40% of SCI cases reported, with violence in close second at 25%. Currently, the highest neurological category is of complete paraplegia followed by incomplete quadriplegia. SCIs often cause many complications due to decreased physical activity and changes in bodily functions. Among treatment options, functional electrical stimulation (FES) is used to restore a variety of physical and physiological functions. Some of the most promising and controversial research lies in the areas of bowel and bladder elimination, gait and exercise training, and also walking. It functions by stimulating the peripheral nerve, sending electrical impulses through electrodes placed on the skin in order to generate a muscular contraction. The goal of FES is to generate purposeful, goal-oriented movement, aimed at completing a task. Based on past research, FES has shown to benefit paralyzed individuals by reducing secondary complications, improving physiological responses, producing bone and muscle changes, and increasing cardiovascular fitness. The purpose of this literature review is to determine whether or not FES produces beneficial functional movement in paraplegics. The procedure used to perform this study will be a literature review based on a collection of journal entries, articles, statistics, and experimentations of scientists, various health professionals, and other researchers