Thierry Keller

A reliable gait phase detection system

A new highly reliable gait phase detection system, which can be used in gait analysis applications and to control the gait cycle of a neuroprosthesis for walking, is described. The system was designed to detect in real-time the following gait phases: stance, heel-off, swing, and heel-strike. The gait phase detection system employed a gyroscope to measure the angular velocity of the foot and three force sensitive resistors to assess the forces exerted by the foot on the shoe sole during walking. A rule-based detection algorithm, which was running on a portable microprocessor board, processed the sensor signals. In the presented experimental study ten able bodied subjects and six subjects with impaired gait tested the device in both indoor and outdoor environments (0-25/spl deg/C). The subjects were asked to walk on flat and irregular surfaces, to step over small obstacles, to walk on inclined surfaces, and to ascend and descend stairs. Despite the significant variation in the individual walking styles the system achieved an overall detection reliability above 99% for both subject groups for the tasks involving walking on flat, irregular, and inclined surfaces. In the case of stair climbing and descending tasks the success rate of the system was above 99% for the able body subjects and above 96% for the subjects with impaired gait. The experiments also showed that the gait phase detection system, unlike other similar devices, was insensitive to perturbations caused by nonwalking activities such as weight shifting between legs during standing, feet sliding, sitting down, and standing up.

Robotic orthosis lokomat: a rehabilitation and research tool.

The aim of this article is to introduce the robotic orthosis Lokomat, developed to automate treadmill training rehabilitation of locomotion for spinal cord injured and stroke patients, to the Functional Electrical Stimulation (FES) and Neuromodulation research communities, and to report on our newly conducted research. We first illustrate the primary use of Lokomat in rehabilitation and focus on control aspects and algorithms associated with robotic rehabilitation of locomotion. Then we describe two applications where the Lokomat was used as a research tool. The first application is closed‐loop control of the FES‐induced shank movement and the second is the development of a neural network model of the spinal locomotor centers. This model was used to derive a neural locomotion controller for the Lokomat.

Improving patient motivation in game development for motor deficit rehabilitation

It has been stated repeatedly that active participation in rehabilitation programs increases the benefit and effectiveness of therapy. In developing robotic devices for stroke rehabilitation, the existing use of boring task interfaces produces a significant reduction in elderly patient motivation. To combine robot-aided therapy with appealing games, then, is not only a matter of creating entertainment, but a real necessity for motor recovery. Besides emphasizing a lack of attention to elderly patients in conceiving games for post-stroke rehabilitation, this paper launches a challenge to two fields with tremendous collaborative potential. As a precursor to this collaboration, the following research consolidates the gaming scenario criteria for both rehabilitation and elderly entertainment. Conclusions are then formed from the adaptability of existing games to identify the direction of future game development.

A reliable, gyroscope based gait phase detection sensor embedded in a shoe insole

This paper describes a new gait phase detection sensor (GPDS) and its application together with a functional electrical stimulation (FES) system for subjects with a drop-foot walking dysfunction. The gait phase detection sensor (sensors and processing unit) is entirely embedded in a shoe insole and detects in real time four gait phases (events) during the gait cycle: stance, heel-off, swing and heel-strike. The gait phase signal is used in a finite state control scheme to time the electrical stimulation sequences in order to generate a motion in the affected leg that is close to a physiological motion. The GPDS uses a miniature gyroscope that measures the rotational velocity of the foot and three force sensitive resistors that measure the force load on the shoe insole. Contrary to other systems using only force sensors, our system can easily differentiate between true walking and weight shifting from one leg to the other during standing. This is achieved through the combination of force sensors and a gyroscope sensor.

Sliding mode closed-loop control of FES controlling the shank movement

Functional electrical stimulation (FES) enables restoration of movement in individuals with spinal cord injury. FES-based devices use electric current pulses to stimulate and excite the intact peripheral nerves. They produce muscle contractions, generate joint torques, and thus, joint movements. Since the underlying neuromuscular-skeletal system is highly nonlinear and time-varying, feedback control is necessary for accurate control of the generated movement. However, classical feedback/closed-loop control algorithms have so far failed to provide satisfactory performance and were not able to guarantee stability of the closed-loop system. Because of this, only open-loop controlled FES devices are in clinical use in spite of their limitations. The purpose of the reported research was to design a novel closed-loop FES controller that achieves good tracking performance and guarantees closed-loop stability. Such a controller was designed based on a mathematical neuromuscular-skeletal model and is founded on a sliding mode control theory. The controller was used to control shank movement and was tested in computer simulations as well as in actual experiments on healthy and spinal cord injured subjects. It demonstrated good robustness, stability, and tracking performance properties.

Neuroprostheses for grasping

Abstract In recent years a number of neuroprostheses have been developed and used to assist stroke and spinal cord injured subjects to restore or improve grasping function. These neuroprostheses clearly demonstrated that the targeted group of subjects can significantly benefit from this technology and that functional electrical stimulation (FES) is a viable method for restoring or improving grasping function. In this article the FES technology is briefly explained and some of the better known neuroprostheses for grasping are discussed. Furthermore, a typical population of subjects that can benefit from this technology is indicated as well as the methodology to select and train these subjects to apply the neuroprosthesis in daily living activities. This article also provides a brief summary of the achieved results with the existing neuroprostheses for grasping and discusses some of the challenges this technology is currently facing. [Neurol Res 2002; 24: 443-452]

Surface-stimulation technology for grasping and walking neuroprostheses

Deals with improving the quality of life in stroke/spinal cord injury subjects with rapid prototyping and portable FES systems. Portable grasping and walking neuroprostheses, developed by the Automatic Control Laboratory at the Swiss Federal Institute of Technology Zurich (ETHZ) and the Paraplegic Center at the University Hospital Balgrist (ParaCare) are discussed. Both neuroprostheses employ surface stimulation technology and are currently used by a number of subjects in daily living activities.

Functional Electrical Stimulation for Grasping and Walking: Indications and Limitations

This review describes the state of art in the field of Functional Electrical Stimulation (FES) and its impact on improving grasping and walking functions in acute and chronic Spinal Cord Injured (SCI) patients. It is argued that during the early rehabilitation period the FES systems with surface stimulation electrodes should be used to assist training of hand and leg movements in SCI patients. Our clinical trials have shown that a number of acute SCI patients with impaired walking and grasping functions could improve these functions due to training with an adjustable FES system to the point that they finally did not need the FES system to carry out these tasks. Other acute SCI patients, who did not recover the desired function, were enabled to perform either walking or grasping with the FES assistance. We believe that the subjects who can perform grasping or walking with the help of FES, and still use the neuroprosthesis 6 months after being subjected to the FES training, should consider the FES system as a prosthetic device in Activities of Daily Living (ADL). Despite the significant technical progress achieved in the last 10 to 15 years in the FES field, there is a general consensus that these systems are not sufficiently advanced and that they need further development. The limited acceptance of the FES technology can be in part explained by the fact that it is not completely mature and that the patients still require daily assistance to use the FES systems. Nevertheless the present FES treatments combined with conventional occupational and physical therapy still remain the most promising approach in rehabilitating SCI patients. In this review, advantages and limitations of different FES systems that are used to restore grasping and walking functions are discussed.Spinal Cord (2001) 39, 403–412.

Transcutaneous functional electrical stimulation for grasping in subjects with cervical spinal cord injury

Study design:Case series.Objectives:To evaluate the benefit, shortcomings and acceptance of a new transcutaneous functional electrical stimulation (FES) technology aimed at improving the grasp function in tetraplegic subjects in acute and postacute rehabilitation.Setting:Spinal cord injury (SCI) centre, university hospital.Methods:Subjects (N=11) with complete or incomplete SCI at C4/5–C7 who started FES 1–67 months after their accident were included. Hand function tests, analysis of video recordings and of written documentation of FES sessions, status of muscle strength, and follow-up query were used as outcome measures.Results:Nine subjects used FES as a neuroprosthesis. Eight demonstrated improved grasp function and performance in activities of daily living. In one subject, no benefit from FES was observed. Two other subjects showed improvements in muscle strength and facilitation of active movement with FES. Four subjects successfully integrated FES as neuroprosthesis in everyday life within the rehabilitation centre. Three received the system for home use. The most relevant reasons for stopping the FES application were: (i) improvement of voluntary grasp function, (ii) physical and psychological problems, (iii) no available stimulator for home use, and (iv) insufficient assistance for electrode placement at home. Shortcomings related to the transcutaneous surface technology (eg pain or coactivation of neighbouring muscles) could usually be reduced, or did not limit the efficiency or acceptance of FES. Individually designed digital or analogue control devices were preferred.Conclusion:Tetraplegic subjects in acute and postacute rehabilitation can profit from a new transcutaneous FES system with respect to functional use and independence. It can be implemented in the rehabilitation programme for muscle strengthening and facilitation of voluntary activity. For a successful application of FES, there is a need for individual electrode placement, stimulation programmes, and FES control devices.

A multi-pad electrode based functional electrical stimulation system for restoration of grasp

BackgroundFunctional electrical stimulation (FES) applied via transcutaneous electrodes is a common rehabilitation technique for assisting grasp in patients with central nervous system lesions. To improve the stimulation effectiveness of conventional FES, we introduce multi-pad electrodes and a new stimulation paradigm.MethodsThe new FES system comprises an electrode composed of small pads that can be activated individually. This electrode allows the targeting of motoneurons that activate synergistic muscles and produce a functional movement. The new stimulation paradigm allows asynchronous activation of motoneurons and provides controlled spatial distribution of the electrical charge that is delivered to the motoneurons. We developed an automated technique for the determination of the preferred electrode based on a cost function that considers the required movement of the fingers and the stabilization of the wrist joint. The data used within the cost function come from a sensorized garment that is easy to implement and does not require calibration. The design of the system also includes the possibility for fine-tuning and adaptation with a manually controllable interface.ResultsThe device was tested on three stroke patients. The results show that the multi-pad electrodes provide the desired level of selectivity and can be used for generating a functional grasp. The results also show that the procedure, when performed on a specific user, results in the preferred electrode configuration characteristics for that patient. The findings from this study are of importance for the application of transcutaneous stimulation in the clinical and home environments.