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

Adaptive control of cyclic movements as muscles fatigue using functional neuromuscular stimulation

For individuals with spinal cord injuries, functional neuromuscular stimulation (FNS) systems can be used to activate paralyzed muscles in order to restore function, provide exercise, or assist in movement therapy. In previous work, the pattern generator/pattern shaper (PG/PS) adaptive controller was evaluated on subjects with spinal cord injuries and was able to automatically adjust stimulation parameters to account for individual subject differences and system response nonlinearities. In this study, the PG/PS control system was utilized in extended trials. Results indicated that the controller adapted stimulation patterns in an online manner to account for changes in system properties due to fatigue.

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.

A pilot study of myoelectrically controlled FES of upper extremity

Functional electrical stimulation (FES) of upper limbs can be used for the recovery of some hand functions on patients with CNS lesions. This study deals with the control of FES by means of myoelectrical activity detected from voluntarily activated paretic muscles. The specific aim of this paper is to evaluate the accuracy of myoelectrical control in terms of produced force and movement. For this purpose, a specific device called myoelectrical controlled functional electrical stimulator (MeCFES) has been developed and applied to six tetraplegic patients with a spinal cord lesion and one stroke hemiplegic patient. Residual myoelectric signals from the paretic wrist extensor (m. extensor carpi radialis, ECR) have been used to control stimulation of either the wrist extension (i.e., the same muscle) or thumb flexion. A tracking test based on a visual feedback of the produced force or movement compared to a reference target trajectory was used to quantify control accuracy. A comparison was made between the tracking performances of each subject with and without the MeCFES and the learning process for two of the subjects were observed during consecutive sessions. Results showed that the wrist extension was improved in three out of five C5 SCI patients and the thumb flexion was largely increased in one incomplete C3 SCI patient. The hemiplegic patient showed limited thumb control with the MeCFES but indicated the possibility of a carry over effect. It was found that a low residual natural force resulted in a less accurate movement but also with a large increase (up to ten times) of the muscle output. On the contrary, persons with a medium residual force obtained a smaller amplification of muscle force with a higher tracking accuracy.

Selectivity and sensitivity of intramuscular and transcutaneous electromyography electrodes

We evaluated the differences in selectivity and sensitivity of intramuscular fine-wire electrodes and transcutaneous electrodes in detecting dynamic electromyography (EMG) signals from extensor digitorum (EDC) and extensor carpi radialis (ECR) muscles during isolated EDC and ECR contractions in two able-bodied subjects. Intramuscular fine-wire electrodes differentiated EDC and ECR EMG activities better than transcutaneous electrodes, and intramuscular fine-wire electrodes recorded higher amplitude signals than transcutaneous electrodes. Data suggest that intramuscular fine-wire electrodes are more selective and sensitive than transcutaneous electrodes in detecting EMG signals from adjacent forearm muscles.

EMG-based prediction of shoulder and elbow kinematics in able-bodied and spinal cord injured individuals

We have evaluated the ability of a time-delayed artificial neural network (TDANN) to predict shoulder and elbow motions using only electromyographic (EMG) signals recorded from six shoulder and elbow muscles as inputs, both in able-bodied subjects and in subjects with tetraplegia arising from C5 spinal cord injury. For able-bodied subjects, all four joint angles (elbow flexion-extension and shoulder horizontal flexion-extension, elevation-depression, and internal-external rotation) were predicted with average root-mean-square (rms) errors of less than 20 degrees during movements of widely different complexities performed at different speeds and with different hand loads. The corresponding angular velocities and angular accelerations were predicted with even lower relative errors. For individuals with C5 tetraplegia, the absolute rms errors of the joint angles, velocities, and accelerations were actually smaller than for able-bodied subjects, but the relative errors were similar when the smaller movement ranges of the C5 subjects were taken into account. These results indicate that the EMG signals from shoulder and elbow muscles contain a significant amount of information about arm moVement kinematics that could be exploited to develop advanced control systems for augmenting or restoring shoulder and elbow movements to individuals with tetraplegia using functional neuromuscular stimulation of paralyzed muscles.

Quantitative evaluation of two methods of control of bilateral stimulated hand grasps in persons with tetraplegia

Electrical stimulation has been applied to the paralyzed muscles of both hands of two persons with tetraplegia using percutaneous and implantable electrodes. Two separate methods of user control were being investigated. The first monitored the myoelectric signals from the user's own sternocleidomastoid muscles and the second monitored wrist joint angle. These signals were used as commands to modify the stimulated grasps. The hands were instrumented to detect the degree of hand closure and grip force and the users matched these to specific target parameters using the controller during tracking tasks. Performance in these tracking tasks was measured quantitatively. Wrist control was found to be less sensitive to the direction of hand opening/closing required than the myoelectric control. The user's performance with the myoelectric control demonstrated sensitivity to the target size and the speed of hand movement in response to the command control. The wrist controller required less training than the myoelectric controller for users to become proficient in its use. Based on these results, the wrist controller and the myoelectric controller both provide successful control of bilateral hand grasp and release. Of the two controllers, the wrist controller is likely to provide the greater ease of use, although it is only available to the population of users with active wrist extension.

Applications of cortical signals to neuroprosthetic control: a critical review

Cortical signals might provide a potential means of interfacing with a neuroprosthesis. Guidelines regarding the necessary control features in terms of both performance characteristics and user requirements are presented, and their implications for the design of a first generation cortical control interface for a neuroprosthesis are discussed.

Electrically stimulated elbow extension in persons with C5/C6 tetraplegia: a functional and physiological evaluation

OBJECTIVE

To measure the effect of electrically stimulated triceps on elbow extension strength, range of motion, and the performance of overhead reaching tasks.

SETTING

Clinical research laboratory.

PARTICIPANTS

Four individuals with spinal cord injuries at the C5 or C6 motor level.

INTERVENTIONS

The participants, who already had an implanted upper extremity neuroprosthesis, were provided with elbow extension through functional electrical stimulation (FES) of the triceps brachii.

MAIN OUTCOME MEASURES

Comparisons of stimulated elbow extension to voluntary elbow extension: (1) evaluations of impairment such as range of motion and strength; (2) performance of a set of functional overhead reaching tasks that required elbow extension; (3) a usage survey (conducted by telephone) to examine use of triceps stimulation in the home and community.

RESULTS

All participants achieved greater range of motion and strength of elbow extension with stimulated triceps versus without. Overall functional task performance improved in 100% of the tasks tested for all but one participant, who showed improvement in 60% of the tasks. Participants reported using the triceps in at least one activity for at least 90% of the days the neuroprosthesis was donned.

Implantable transducer for two-degree of freedom joint angle sensing

An implantable joint angle transducer (IJAT) was developed to provide command-control and feedback-control information for chronic use with functional neuromuscular stimulation (FNS) neuroprostheses. The IJAT uses Hall effect sensors to transduce joint angle. A titanium encapsulated array of Hall effect sensors and support circuitry is surgically implanted in one bone, and a similarly encapsulated permanent magnet in an opposing bone, across a joint. The IJAT provides consistent, reliable, high quality signals that reflect joint movement from midsized two-degree-of-freedom joints. IJAT's were implanted using a chronic in vivo dog model to demonstrate the feasibility of implantation and periodic measurement techniques, and to validate modeling techniques used for prediction of function and calibration. The flexion resolution ranged from 0.4 to 3.0 degrees over a range of 115 degrees. The maximum deviation from a linear response was 9 degrees. The resolution and linearity depend on several transducer and joint geometry parameters, and can be predicted prior to implantation and calibrated after implantation. The results of this study 1) defined the most appropriate hermetic capsule designs for the IJAT sensor and magnet, 2) defined the best orientation of the magnetic field to optimize device function, 3) provided a computer model of the IJAT to aid in placement, calibration, and evaluation of the device, 4) verified the surgical techniques used to implant the device, and 5) verified the long-term functionality and the biocompatibility of the device.