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

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

Upper-limb exercise in tetraplegia using functional electrical stimulation

Cervical spinal cord injury can result in dysfunction in both the lower and upper limbs (tetraplegia), andmay be accompanied by a range of secondary complications. The degree of upper-limb dysfunctiondepends upon the level and completeness of the lesion; in this paper we consider tetraplegics with a neurological level in the range C4-C6. A person with a C5- or C6-level injury will generally retain control of the shoulder and elbow flexor muscles biceps), but will have no control of the hand, wrist or elbow extensors (triceps).With a complete C4 injury voluntary control of the entire arm is lost. Thus, we propose that functional electrical stimulation (FES) of the biceps and triceps muscles may enhance the efficacy of cyclical upper-limb exercise. Alternatives for partial restoration of function include tendon transfer surgery or mechanical orthoses1. Previous FES research for C4-C6 tetraplegics has focused on systems for hand function2,3 and improved working area (i.e. overhead reach)4,5,6,7, but the provision of upper-limb exercise modalities using FES assistance has been neglected. This is important because the lack of effective exercise can lead rapidly to severe cardiopulmonary deconditioning in this population

Feedback control of unsupported standing

This paper presents the results of continuing work on feedback control of unsupported standing in paraplegia. Our experimental setup considers a situation in which all joints above the ankle are braced, and stabilising torque at the ankle is generated by stimulation of the plantarflexors. A previous study showed that short periods of unsupported standing with paraplegic subjects could be achieved. In order to improve consistency and reliability of unsupported standing we are currently investigating several modifications to the control strategy. The paper reports progress towards this goal

Automatic electrical stimulation of abdominal wall muscles increases tidal volume and cough peak flow in tetraplegia

<p>Paralysis of the respiratory muscles in people with tetraplegia affects their ability to breathe and contributes to respiratory complications. Surface functional electrical stimulation (FES) of abdominal wall muscles can be used to increase tidal volume (V_{T}) and improve cough peak flow (CPF) in tetraplegic subjects who are able to breathe spontaneously.</p> <p>This study aims to evaluate the feasibility and effectiveness of a novel abdominal FES system which generates stimulation automatically, synchronised with the subjects' voluntary breathing activity. Four subjects with complete tetraplegia (C4-C6), breathing spontaneously, were recruited.</p> <p>The automatic stimulation system ensured that consistent stimulation was achieved. We compared spirometry during unassisted and FES-assisted quiet breathing and coughing, and measured the effect of stimulation on end-tidal CO_2 (EtCO_2) during quiet breathing.</p> <p>The system dependably recognised spontaneous respiratory effort, stimulating appropriately, and was well tolerated by patients. Significant increases in V_T during quiet breathing (range 0.05–0.23 L) and in CPF (range 0.04–0.49 L/s) were observed. Respiratory rate during quiet breathing decreased in all subjects when stimulated, whereas minute ventilation increased by 1.05–2.07 L/min. The changes in EtCO_2 were inconclusive.</p> <p>The automatic stimulation system augmented spontaneous breathing and coughing in tetraplegic patients and may provide a potential means of respiratory support for tetraplegic patients with reduced respiratory capacity.</p&gt

Arm-cranking exercise assisted by Functional Electrical Stimulation in C6 tetraplegia: a pilot study

Tetraplegic volunteers undertook progressive exercise training, using novel systems for arm-cranking exercise assisted by Functional Electrical Stimulation (FES). The main aim was to determine potential training effects of FES-assisted arm-crank ergometry (FES-ACE) on upper limb strength and cardiopulmonary {fitness} in tetraplegia. Surface FES was applied to the biceps and triceps during exercise on an instrumented ergometer. Two tetraplegic volunteers with C6 Spinal Cord Injury (SCI) went through muscle strengthening, baseline exercise testing and three months of progressive FES-ACE training. Repeat exercise tests were carried out every four weeks during training, and post-training, to monitor upper-limb strength and cardiopulmonary fitness. At each test point, an incremental test was carried out to determine peak work rate, peak oxygen uptake, gas exchange threshold and oxygen uptake-work rate relationship during FES-ACE. Peak oxygen uptake for Subject A increased from 0.7 l/min to 1.1 l/min, and peak power output increased from 7 W to 38 W after FES-ACE training. For Subject B, peak oxygen uptake was unchanged, but peak power output increased from 3 W to 8 W. These case studies illustrate potential benefits of FES-ACE in tetraplegia, but also the differences in exercise responses between individuals. Keywords: electrical stimulation; spinal cord injury; cardiopulmonary fitness; rehabilitation; tetraplegi

Dynamic balance training with sensory electrical stimulation in chronic stroke patients

A case study investigating the impact of sensory electrical stimulation during perturbed stance in one chronic stroke patient is presented. A special apparatus called the BalanceTrainer was used. It allows the application of perturbations to neurologically impaired people during standing, while protecting the subject from falling. The subject underwent two different periods of perturbation training, each lasting ten days. During the first period the subject was perturbed in eight different directions. During the second period the subject was also perturbed, but was assisted by sensory electrical stimulation of the soleus, tibialis anterior, tensor fascia latae, and vastus muscles in the impaired leg. After each period of training an assessment was carried out to measure the forces the subject applied on the ground via two force plates. The subject improved his ability to balance throughout the training, with the largest improvements during the final period when electrical stimulation was used

Non-intrusive real-time breathing pattern detection and classification for automatic abdominal functional electrical stimulation

Abdominal Functional Electrical Stimulation (AFES) has been shown to improve the respiratory function of people with tetraplegia. The effectiveness of AFES can be enhanced by using different stimulation parameters for quiet breathing and coughing. The signal from a spirometer, coupled with a facemask, has previously been used to differentiate between these breath types. In this study, the suitability of less intrusive sensors was investigated with able-bodied volunteers. Signals from two respiratory effort belts, positioned around the chest and the abdomen, were used with a Support Vector Machine (SVM) algorithm, trained on a participant by participant basis, to classify, in real-time, respiratory activity as either quiet breathing or coughing. This was compared with the classification accuracy achieved using a spirometer signal and an SVM. The signal from the belt positioned around the chest provided an acceptable classification performance compared to the signal from a spirometer (mean cough (<i>c</i>) and quiet breath (<i>q</i>) sensitivity (<i>Se</i>) of <i>Se<sup>c</sup></i> = 92.9% and <i>Se<sup>q</sup></i> = 96.1% vs. <i>Se<sup>c</sup></i> = 90.7% and <i>Se<sup>q</sup></i> = 98.9%). The abdominal belt and a combination of both belt signals resulted in lower classification accuracy. We suggest that this novel SVM classification algorithm, combined with a respiratory effort belt, could be incorporated into an automatic AFES device, designed to improve the respiratory function of the tetraplegic population

Trajectory generation for road vehicle obstacle avoidance using convex optimization

This paper presents a method for trajectory generation using convex optimization to find a feasible, obstacle-free path for a road vehicle. Consideration of vehicle rotation is shown to be necessary if the trajectory is to avoid obstacles specified in a fixed Earth axis system. The paper establishes that, despite the presence of significant non-linearities, it is possible to articulate the obstacle avoidance problem in a tractable convex form using multiple optimization passes. Finally, it is shown by simulation that an optimal trajectory that accounts for the vehicle’s changing velocity throughout the manoeuvre is superior to a previous analytical method that assumes constant speed

Intermittent control of unstable multivariate systems

© 2015 IEEE.A sensorimotor architecture inspired from biological, vertebrate control should (i) explain the interface between high dimensional sensory analysis, low dimensional goals and high dimensional motor mechanisms and (ii) provide both stability and flexibility. Our interest concerns whether single-input-single-output intermittent control (SISO-IC) generalized to multivariable intermittent control (MIC) can meet these requirements