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.     

Simultaneous and proportional estimation of hand kinematics from EMG during mirrored movements at multiple degrees-of-freedom

This paper proposes and tests on able-bodied subjects a control strategy that can be practically applied in unilateral transradial amputees for simultaneous and proportional control of multiple degrees-of-freedom (DOFs). We used artificial neural networks to estimate kinematics of the complex wrist/hand from high-density surface electromyography (EMG) signals of the contralateral limb during mirrored bilateral movements in free space. The movements tested involved the concurrent activation of wrist flexion/extension, radial/ulnar deviation, forearm pronation/supination, and hand closing. The accuracy in estimation was in the range 79%-88% (r(2) index) for the four DOFs in six able-bodied subjects. Moreover, the estimation of the pronation/supination angle (wrist rotation) was influenced by the reduction in the number of EMG channels used for the estimation to a greater extent than the other DOFs. In conclusion, the proposed method and set-up provide a viable means for proportional and simultaneous control of multiple DOFs for hand prostheses.     

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     

Simulated feedforward neural network coordination of hand grasp and wrist angle in a neuroprosthesis.

This study presents a possible solution of the general problem of coordinating muscle stimulation in a neuroprosthesis when multiarticular muscles introduce mechanical coupling between joints. In a hand-grasp neuroprosthesis, extrinsic hand muscles cross the wrist joint and introduce large wrist flexion moments during grasp. In order to control hand grasp and wrist angle independently, a controller must take the mechanical coupling into account. In simulation, we investigated the use of artificial neural networks to coordinate hand and wrist muscle stimulation. The networks were trained with data that is easily obtained experimentally. Feedforward control showed excellent hand and wrist coordination when the properties of the system were fixed and there were known external loads. Predictable disturbances (e.g., gravity acting on the hand) can be compensated by sensing arm orientation. However, since wrist angle is sensitive to unpredictable disturbances (e.g., fatigue or object weight), voluntary intervention or feedback control may be required to reduce residual errors.     

Selectivity and resolution of surface electrical stimulation for grasp and release

Electrical stimulation of arm and hand muscles can be a functional tool for patients with motor dysfunction. Sufficient stimulation of finger and thumb musculature can support natural grasping function. Yet it remains unclear how different grasping movements can be selectively supported by electrical stimulation. The goal of this study is to determine to what extent activation of individual fingers is possible with surface electrical stimulation for the purpose of rehabilitation following stroke. The extensor digitorum communis (EDC) muscle, flexor pollicis longus (FPL) muscle, and the thenar muscle group, all involved in grasp and release, were selected for stimulation. The evoked forces in individual fingers were measured. Stimulation thresholds and selective ranges were determined for each subject. Electrode locations where the highest selective range occurred were compared between subjects and influences of different isometric wrist positions were assessed. In all subjects selective stimulation of middle finger extension and thumb flexion was possible. In addition, selective stimulation of index and ring finger extension was possible in most cases. In nine out of the ten EDC subjects we were able to stimulate three or all four fingers selectively. However, large variability in electrode locations for high selectivity was observed between the subjects. Within the designs of grasping prostheses and grasping rehabilitation devices, the variability of electrode locations should be taken into account. The results of our study facilitate the optimization of such designs and favour a design which allows individualized stimulation locations.     

The effect of joint angle on the timing of muscle contractions elicited by neuromuscular electrical stimulation

Neuromuscular electrical stimulation was used to evoke isometric knee extension contractions in seven individuals with spinal cord injury (SCI) and the time for knee extension torque to rise and fall was measured across a range of knee angles. The stimulated muscles took more than twice as long to develop 50% of maximum torque at an angle of 15 degrees, compared to an angle of 90 degrees. This time difference comprised both an increased delay before torque rose above resting levels (31 +/- 3 ms at 90 degrees, 67 +/- 24 ms at 15 degrees), and a prolonged duration over which torque was rising (72 +/- 14 ms at 90 degrees, 140 +/- 62 ms at 15 degrees). There was no change, however, in the time taken for torque to fall after cessation of stimulation at different knee angles (58 +/- 5-ms delay, 60 +/- 11-ms fall time). The difference in torque rise time with joint angle has implications for modeling functional activities that differ greatly in their joint angles. This study provides regression equations whereby activation times for the quadriceps muscles of individuals with SCI can be predicted for specific angles of knee flexion.     

Joint angle control by FES using a feedback error learning controller.

The feedback error learning (FEL) scheme was studied for a functional electrical stimulation (FES) controller. This FEL controller was a hybrid regulator with a feedforward and a feedback controller. The feedforward controller learned the inverse dynamics of a controlled object from feedback controller outputs while control. A four-layered neural network and the proportional-integral-derivative (PID) controller were used for each controller. The palmar/dorsi-flexion angle of the wrist was controlled in both computer simulation and FES experiments. Some controller parameters, such as the learning speed coefficient and the number of neurons, were determined in simulation using an artificial forward model of the wrist. The forward model was prepared by using a neural network that can imitate responses of subject's wrist to electrical stimulation. Then, six able-bodied subjects' wrist was controlled with the FEL controller by delivering stimuli to one antagonistic muscle pair. Results showed that the FEL controller functioned as expected and performed better than the conventional PID controller adjusted by the Chien, Hrones and Reswick method for a fast movement with the cycle period of 2 s, resulting in decrease of the average tracking error and shortened delay in the response. Furthermore, learning iteration was shortened if the feedforward controller had been trained in advance with the artificial forward model.     

Synergistic control of stimulated pronosupination with thestimulated grasp of persons with tetraplegia

The control of stimulated forearm pronosupination in concert with stimulated hand grasp of persons with tetraplegia has been investigated. It has been shown that hand grasp stability increased as supination was achieved. In accordance with this, a strategy of object acquisition has been proposed incorporating pronosupination and hand grasp. It has been proposed that, after object acquisition in the pronated posture, that supination be used to increase grasp stability. Three types of pronosupination control which act in synchrony with grasp were implemented incorporating this principle. The three types used were position-controlled pronator stimulation, touch-controlled pronator stimulation, and constant pronation stimulation. These controllers played a supporting role to the separate user control of hand grasp and release. The three controllers were evaluated and compared using a standardized test procedure that incorporated stimulated pronosupination control with stimulated grasp. Such methods of pronosupination control are likely to provide enhanced options for improving upper extremity function using electrical stimulation     

Asynchronous decoding of dexterous finger movements using M1 neurons.

Previous efforts in brain-machine interfaces (BMI) have looked at decoding movement intent or hand and arm trajectory, but current cortical control strategies have not focused on the decoding of 3 actions such as finger movements. The present work demonstrates the asynchronous decoding (i.e., where cues indicating the onset of movement are not known) of individual and combined finger movements. Single-unit activities were recorded sequentially from a population of neurons in the M1 hand area of trained rhesus monkeys during flexion and extension movements of each finger and the wrist. Nonlinear filters were designed to detect the onset of movement and decode the movement type from randomly selected neuronal ensembles (assembled from individually recorded single-unit activities). Average asynchronous decoding accuracies as high as 99.8%, 96.2%, and 90.5%, were achieved for individuated finger and wrist movements with three monkeys. Average decoding accuracy was still 92.5% when combined movements of two fingers were included. These results demonstrate that it is possible to asynchronously decode dexterous finger movements from a neuronal ensemble with high accuracy. This work takes an important step towards the development of a BMI for direct neural control of a state-of-the-art, multifingered hand prosthesis.     

The function of the finger intrinsic muscles in response to electrical stimulation.

The actions of the dorsal interosseous, volar interosseous, and lumbrical muscles were investigated using applied electrical stimulation and recording the moments that were generated across the metacarpophalangeal joint in flexion/extension and abduction/adduction, the proximal interphalangeal joint in flexion/extension, and the distal interphalangeal joint in flexion/extension. These measurements were made isometrically at various joint angles and levels of stimulation with both able bodied subjects and persons who had sustained tetraplegia. It was determined that the dorsal interossei, including the first, were strong abductors of the fingers and generated a significant moment in metacarpophalangeal (MP) joint flexion and interphalangeal (IP) joint extension. The volar interossei were the primary adductors of the fingers, as well as providing a significant moment in MP joint flexion and IP joint extension. The lumbrical muscles were found to be MP joint flexors and IP joint extensors, although the moments that were generated were on average 70% lower than the interossei. The role of the lumbricals as finger abductors or adductors could not be determined from the data. This information on the actions and moment generating capabilities of the intrinsic muscles led to the incorporation of the interossei into electrically induced hand grasp provided by an implanted neuroprosthesis. The evaluation of the intrinsic muscles in the neuroprosthesis was accomplished by recording the moment generating capabilities of these muscles across each of the joints of the finger. These muscles were capable of generating moments that were 80-90% of the average attained by the able bodied subjects, and have provided a substantial improvement to the electrically induced hand grasp.     

The effects of trunk stimulation on bimanual seated workspace

This study explores the effects of functional electrical stimulation (FES) of the lumbar trunk extensors on the seated posture and bimanual workspace of subjects with spinal cord injury (SCI). Four subjects with motor complete SCI with implanted intramuscular stimulating electrodes to activate the lumbar erector spinae were studied. The positions of markers on the pelvis, trunk, and hands were monitored by a motion capture system during bimanual reaching maneuvers. To define three-dimensional functional workspace boundaries, subjects swept their hands through the extremes of their range of motion without losing balance while sitting. To characterize forward reach, subjects reached to targets in the sagittal plane while carrying various masses with and without FES. Reaching trials were rated on the seven-point usability rating scale to determine effort and subject preference and change in pelvic angle with stimulation was monitored. There was a consistent change in the seated posture with FES in all subjects that resulted in significant forward or upward (6.85 cm +/- 2.15 cm) shifts in the workspace. Workspace volumes increased for two of the four subjects tested. FES caused significant anterior rotation of the pelvis to restore a more natural lumbar curve without a backrest (19.81 degrees +/- 8.75 degrees). With a backrest, the change in posture with FES allowed individuals with SCI to reach further in the sagittal plane and carry heavier masses by shifting the trunk, allowing increased elbow extension, or a combination of the two mechanisms. Reaching with FES was consistently preferred over reaching without FES. This preliminary study is encouraging for future research on trunk stability and reaching ability with FES.     

Receptive Field Characteristics Under Electrotactile Stimulation of the Fingertip

Skin on human fingertips has high concentrations of mechanoreceptors, which are used to provide fine resolution tactile representations of our environment. Here, we explore the ability to discriminate electrotactile stimulation at four sites on the fingertip. Electrical stimulation was delivered to arrays of electrodes centered on the index fingertip (volar aspect). Accuracy of discrimination was tested by examining electrode size, interelectrode spacing, and stimulation frequency as primary factors. Electrical stimulation was delivered at 2 mA with the pulse width modulated to be at (or above) perceptual threshold at 25 and 75 Hz and an average pulse width of 1.03 ms ( $+/-$0.70 ms standard deviation). Discrimination of the stimulated locations under this stimulation paradigm was significantly above chance level in all cases. Subjects' ability to discriminate stimulus location was not significantly influenced by electrode size or stimulation frequency when considered as separate factors. However, increased electrode spacing significantly increased subjects' ability to discriminate the location of the stimulated electrode. Further analysis revealed that errors were only significantly reduced along the medial-lateral direction with increasing interelectrode spacing. These results suggest that the electrotactile stimulus localization on the fingertip has some directional dependency, in addition to its dependency on interelectrode spacing. The neural mechanisms underlying this phenomenon are discussed in relation to electrical stimulus transduction characteristics of tactile mechanoreceptors.      

Analysis of arm trajectories of everyday tasks for the development of an upper-limb orthosis.

Spatiotemporal arm and body movements of able-bodied subjects performing nine everyday tasks were recorded for the purpose of guiding the development of an upper-limb orthosis. To provide a user the opportunity to carry out these tasks with natural movements, the orthosis should allow replication of the measured trajectories. We outline the orthosis architecture, which supports the user's upper arm and forearm, and analyze the movement data to obtain orthosis design specifications. Trajectories were obtained using six-degree-of-freedom magnetic position sensors affixed to the wrist, elbow, shoulder, trunk and head. Elbow trajectory data were decomposed into ranges along the principle Cartesian axes to provide a generally useful envelope measure. The smallest Cartesian parallel-piped that contained the elbow trajectories for most tasks was approximately 30 cm front/back, 15 cm side/side, and 17 cm up/down. A rough lower bound estimate obtained by asking subjects to repeat the tasks while minimizing elbow movement substantially reduced movement in the up/down and side/side dimensions. Elbow angles were generally in the range 50 degrees-150 degrees, and the angle of the forearm with respect to vertical was 10 degrees-110 degrees. Raw trajectory data may be downloaded from www://asel.udel.edu/robotics/orthosis/range.h tml.     

Hip and trunk stability in paraplegic electrically augmented gait

Research conducted to investigate functional electrical stimulation in the paraplegic individual to provide functional walking is reviewed. To understand better the problems of hip and trunk stability, crutch walking video tapes depicting trial crutch walking sessions experienced by four implanted complete paraplegic individuals were reviewed and all segments demonstrating instability were copied to provide a tape of walking errors. Additional information was gathered from direct observations of similar episodes during muscle programming sessions and exercise walking sessions using a rolling walker. Attempts to use forearm crutches to replace the rolling walker resulted in numerous gait deviations at the hip and spine, the first being a strong tendency to lean forward. It is postulated that adequate hip and trunk stability using electrical stimulation can be achieved through a combination of additional subject training, improved muscle implantation techniques, and improved programming techniques     

Reciprocal EMG control of elbow extension by FES

Elbow extension is critical in performing activities of daily living. Individuals with a C5-C6 spinal cord injury have paralyzed elbow extensors, yet retain weak to strong voluntary control of elbow flexion. Previous studies have shown that functional electrical stimulation (FES) of the triceps provides sufficient elbow extension strength and control to greatly improve function. With triceps stimulation applied at a constant level, elbow angle is controlled naturally by voluntary flexion opposing the stimulated extension-referred to as voluntary antagonist control. We have investigated an alternative reciprocal control scheme employing biceps electromyogram. (EMG) to modulate triceps stimulation. With reciprocal control, increasing biceps EMG proportionally reduces triceps stimulation. A personal computer (PC)-based lab system was designed to test the feasibility of reciprocal control. Reciprocal control increased the range of elbow moments, was stable during maintained elbow angle or isometric moment, and used less stimulation. Reciprocal control of triceps stimulation using biceps EMG is an effective method for restoring elbow extension to C5-C6 spinal cord injury patients, and could be extended to other situations where a voluntarily controlled muscle can be opposed by stimulating an antagonist     

Excitability of chronic hemiparetic muscles: determination of chronaxie values and strength-duration curves and its implication in functional electrical stimulation.

Central nervous system disorders affect the anatomy and physiology of the lower motoneuron. This fact has an impact on the stimulation parameters, especially on the duration of the stimulating impulses, for functional electrical stimulation in chronic hemiparetic patients. The aim of this study was thus to test the excitability and to determine chronaxie values and strength-duration curves of weak wrist and finger extensor muscles and spastic finger and wrist flexor muscles in the hemiparetic arm. Twelve patients with chronic hemiplegia (>6 months after the onset of the cerebral lesion) participated in the study. A constant current stimulator was used. As to chronaxie values no significant differences were found between the extensor muscles (mean+/-SD: 0.44+/-0.16 ms) and flexor muscles (mean+/-SD: 0.36+/-0.22 ms). A moderate variability was seen for both extensor muscles (0.2-0.8 ms) and flexor muscles (0.1-0.9 ms). These values are well within the normal range determined for innervated muscles. All strength-duration curves were completely normal for each muscle. We conclude that in chronic hemiparetic muscles, impulses of the same duration can be used as in muscles of healthy subjects.     

基于GA-SVR模型的肌力康复电刺激系统的设计研究

为了实现康复电刺激系统治疗参数的个性化定制及实时调整,提出了一种基于调制中频电刺激的下肢肌力康复闭环电刺激系统。设计低频调制中频刺激电路,基于遗传算法建立了电刺激参数与膝关节角度之间的支持向量机回归预测模型,并搭建基于模糊内模控制PID的闭环反馈系统,以达到更精确稳定的参数设置效果。通过膝关节运动实验表明,被试者在无痛感的前提下更接近预期的关节运动轨迹,30组膝关节运动角度与预期值最大均方根误差为10.21°,最小均方根误差为5.48°。相比传统低频电刺激,肌电平均振幅具有20μV以上提升。本文提出的电刺激系统参数可实现因人而异,且可根据闭环反馈结果进行实时调整,该系统能有效活化肌肉、提升肌力,在肌力康复步态训练中有较好的应用前景。     

Automatic determination of synergies by radial basis function artificial neural networks for the control of a neural prosthesis.

This paper describes an automatic method for synthesizing the control for a neural prosthesis (NP) that could augment elbow flexion/extension and forearm pronation/supination in persons with hemiplegia. The basis for the control was a synergistic model of reaching and grasping that uses temporal and spatial synergies between the arm and body segments. The synergies were determined from the movement data measured in nondisabled persons during the performance of functional tasks. The work space was divided into six zones: distance (two attributes) and laterality (three attributes). Radial basis function artificial neural networks (RBF ANN) were used to determine synergies. Sets of RBF ANN characterized with good generalization were selected as control laws for elbow flexion/extension and forearm pronation/supination. The validation was performed for three categories: inter-subject, distance, and laterality generalization. For all of the defined spatial synergies, the correlation was high for inter-subject and distance, yet low for the laterality scenario. This suggests the necessity for implementing different maps for different directions, but the same maps for different distances. The natural movements of the upper arm then drive the lower arm (elbow flexion/extension and forearm pronation/supination) in a way that is very well suited for the administration of functional electrical therapy (FET) in persons with hemiplegia soon after the onset of impairment.     

基于模式控制的四脊喇叭馈源设计

四脊喇叭馈源具有较宽的工作频带,但随着频率变化波束宽度难于保持恒定,导致照射效率降低。为了提高天线的口径效率,提出了一种通过控制馈源口面模式设计四脊喇叭馈源的方法。首先以天线口径效率为目标,通过优化得出喇叭口面上的最优模式比例,然后通过改变四脊喇叭的结构参数来调控其口面的模比,使其逐渐逼近最优模比。利用该设计方法,设计了一个半照射角为40°的四脊喇叭馈源,在3∶1带宽内,方向图波束宽度恒定且具有旋转对称性,天线口径效率优于60%。     

A study of shoulder motions as a control source for adolescents with C4 level SCI.

This study quantitatively examined and compared the shoulder motions of C4 level spinal cord injury (SCI), C5 level SCI, and able-bodied persons as a command source. The study was motivated by both the success of shoulder control in functional electrical stimulation (FES) systems designed for C5 level SCI people and the lack of quantitative information on the shoulder motion of persons with C4 level SCI. A dual-axis transducer was used to monitor the elevation/depression and protraction/retraction angles of each subject's shoulder while they performed three experimental sections which examined: the range of active shoulder motion; the ability to move incrementally to discrete positions with the aid of visual feedback; and the ability to hold discrete shoulder positions for an extended period without visual feedback. Results indicated that each group had the largest average shoulder displacements (abled = 23 degrees +/- 4 degrees, C5's = 14 degrees +/- 3 degrees, and C4's = 9 degrees +/- 3 degrees) while attempting to elevate and that on average the C4 group had the smallest range of active shoulder motion. No statistically significant differences between the groups were found in either the accuracy or stability of reaching discrete positions with the aid of visual feedback or in the accuracy of holding discrete shoulder positions for an extended period without visual feedback. The results suggest that within their limited range of motion the individuals with C4 level SCI retained shoulder control sufficient for use as an neuroprosthetic command interface.