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Abstract Background Restoring or improving seated stability after spinal cord injury (SCI) can improve the ability to perform activities of daily living by providing a dynamic, yet stable, base for upper extremity motion. Seated stability can be obtained with activation of the otherwise paralyzed trunk and hip musculature with neural stimulation, which has been shown to extend upper limb reach and improve seated posture. Methods We implemented a proportional, integral, derivative (PID) controller to maintain upright seated posture by simultaneously modulating both forward flexion and lateral bending with functional neuromuscular stimulation. The controller was tested with a functional reaching task meant to require trunk movements and impart internal perturbations through rapid changes in inertia due to acquiring, moving, and replacing objects with one upper extremity. Five subjects with SCI at various injury levels who had received implanted stimulators targeting their trunk and hip muscles participated in the study. Each subject was asked to move a weighted jar radially from a center home station to one of three target stations. The task was performed with the controller active, inactive, or with a constant low level of neural stimulation. Trunk pitch (flexion) and roll (lateral bending) angles were measured with motion capture and plotted against each other to generate elliptical movement profiles for each task and condition. Postural sway was quantified by calculating the ellipse area. Additionally, the mean effective reach (distance between the shoulder and wrist) and the time required to return to an upright posture was determined during reaching movements. Results Postural sway was reduced by the controller in two of the subjects, and mean effective reach was increased in three subjects and decreased for one. Analysis of the major direction of motion showed return to upright movements were quickened by 0.17 to 0.32 s. A 15 to 25% improvement over low/no stimulation was observed for four subjects. Conclusion These results suggest that feedback control of neural stimulation is a viable way to maintain upright seated posture by facilitating trunk movements necessary to complete reaching tasks in individuals with SCI. Replication of these findings on a larger number of subjects would be necessary for generalization to the various segments of the SCI population.

Spinal cord injury (SCI) can cause paralysis of trunk and hip musculature that negatively impacts seated balance and ability to lean away from an upright posture and interact fully with the environment. Constant levels of electrical stimulation of peripheral nerves can activate typically paralyzed muscles and aid in maintaining a single upright seated posture. However, in the absence of a feedback controller, such seated postures and leaning motions are inherently unstable and unable to respond to perturbations. Three individuals with motor complete SCI who had previously received a neuroprosthesis capable of activating the hip and trunk musculature volunteered for this study. Subject-specific muscle synergies were identified through system identification of the lumbar moments produced via neural stimulation. Synergy-based calculations determined the real-time stimulation parameters required to assume leaning postures. When combined with a proportional, integral, derivative (PID) feedback controller and an accelerometer to infer trunk orientation, all individuals were able to assume non-erect postures of 30–40° flexion and 15° lateral bending. Leaning postures increased forward reaching capabilities by 10.2, 46.7, and 16 cm respectively for each subject when compared with no stimulation. Additionally, the leaning controllers were able to resist perturbations of up to 90 N, and all subjects perceived the leaning postures as moderately to very stable. Implementation of leaning controllers for neuroprostheses have the potential of expanding workspaces, increasing independence, and facilitating activities of daily living for individuals with paralysis.

Background: Restoring or improving seated stability after spinal cord injury (SCI) can improve the ability to perform activities of daily living by providing a dynamic, yet stable, base for upper extremity motion. Seated stability can be obtained with activation of the otherwise paralyzed trunk and hip musculature with neural stimulation, which has been shown to extend upper limb reach and improve seated posture. Methods: We implemented a proportional, integral, derivative (PID) controller to maintain upright seated posture by simultaneously modulating both forward flexion and lateral bending with functional neuromuscular stimulation. The controller was tested with a functional reaching task meant to require trunk movements and impart internal perturbations through rapid changes in inertia due to acquiring, moving, and replacing objects with one upper extremity. Five subjects with SCI at various injury levels who had received implanted stimulators targeting their trunk and hip muscles participated in the study. Each subject was asked to move a weighted jar radially from a center home station to one of three target stations. The task was performed with the controller active, inactive, or with a constant low level of neural stimulation. Trunk pitch (flexion) and roll (lateral bending) angles were measured with motion capture and plotted against each other to generate elliptical movement profiles for each task and condition. Postural sway was quantified by calculating the ellipse area. Additionally, the mean effective reach (distance between the shoulder and wrist) and the time required to return to an upright posture was determined during reaching movements. Results: Postural sway was reduced by the controller in two of the subjects, and mean effective reach was increased in three subjects and decreased for one. Analysis of the major direction of motion showed return to upright movements were quickened by 0.17 to 0.32 s. A 15 to 25% improvement over low/no stimulation was observed for four subjects. Conclusion: These results suggest that feedback control of neural stimulation is a viable way to maintain upright seated posture by facilitating trunk movements necessary to complete reaching tasks in individuals with SCI. Replication of these findings on a larger number of subjects would be necessary for generalization to the various segments of the SCI population. [ABSTRACT FROM AUTHOR]

Abstract Background The leading cause of injury for manual wheelchair users are tips and falls caused by unexpected destabilizing events encountered during everyday activities. The purpose of this study was to determine the feasibility of automatically restoring seated stability to manual wheelchair users with spinal cord injury (SCI) via a threshold-based system to activate the hip and trunk muscles with electrical stimulation during potentially destabilizing events. Methods We detected and classified potentially destabilizing sudden stops and turns with a wheelchair-mounted wireless inertial measurement unit (IMU), and then applied neural stimulation to activate the appropriate muscles to resist trunk movement and restore seated stability. After modeling and preliminary testing to determine the appropriate inertial signatures to discriminate between events and reliably trigger stimulation, the system was implemented and evaluated in real-time on manual wheelchair users with SCI. Three participants completed simulated collision events and four participants completed simulated rapid turns. Data were analyzed as a series of individual case studies with subjects acting as their own controls with and without the system active. Results The controller achieved 93% accuracy in detecting collisions and right turns, and 100% accuracy in left turn detection. Two of the three subjects who participated in collision testing with stimulation experienced significantly decreased maximum anterior-posterior trunk angles (p

This pilot study investigated the potential of using trunk acceleration feedback control of center of pressure (COP) against postural disturbances with a standing neuroprosthesis following paralysis. Artificial neural networks (ANNs) were trained to use three-dimensional trunk acceleration as input to predict changes in COP for able-bodied subjects undergoing perturbations during bipedal stance. Correlation coefficients between ANN predictions and actual COP ranged from 0.67 to 0.77. An ANN trained across all subject-normalized data was used to drive feedback control of ankle muscle excitation levels for a computer model representing a standing neuroprosthesis user. Feedback control reduced average upper-body loading during perturbation onset and recovery by 42% and peak loading fby 29% compared with optimal, constant excitation. [ABSTRACT FROM AUTHOR]

Abstract Background Implanted motor system neuroprostheses can be effective at increasing personal mobility of persons paralyzed by spinal cord injuries. However, currently available neural stimulation systems for standing employ patterns of constant activation and are unreactive to changing postural demands. Methods In this work, we developed a closed-loop controller for detecting forward-directed body disturbances and initiating a stabilizing step in a person with spinal cord injury. Forward-directed pulls at the waist were detected with three body-mounted triaxial accelerometers. A finite state machine was designed and tested to trigger a postural response and apply stimulation to appropriate muscles so as to produce a protective step when the simplified jerk signal exceeded predetermined thresholds. Results The controller effectively initiated steps for all perturbations with magnitude between 10 and 17.5 s body weight, and initiated a postural response with occasional steps at 5% body weight. For perturbations at 15 and 17.5% body weight, the dynamic responses of the subject exhibited very similar component time periods when compared with able-bodied subjects undergoing similar postural perturbations. Additionally, the reactive step occurred faster for stronger perturbations than for weaker ones (p

Abstract Background Functional neuromuscular stimulation, lower limb orthosis, powered lower limb exoskeleton, and hybrid neuroprosthesis (HNP) technologies can restore stepping in individuals with paraplegia due to spinal cord injury (SCI). However, a self-contained muscle-driven controllable exoskeleton approach based on an implanted neural stimulator to restore walking has not been previously demonstrated, which could potentially result in system use outside the laboratory and viable for long term use or clinical testing. In this work, we designed and evaluated an untethered muscle-driven controllable exoskeleton to restore stepping in three individuals with paralysis from SCI. Methods The self-contained HNP combined neural stimulation to activate the paralyzed muscles and generate joint torques for limb movements with a controllable lower limb exoskeleton to stabilize and support the user. An onboard controller processed exoskeleton sensor signals, determined appropriate exoskeletal constraints and stimulation commands for a finite state machine (FSM), and transmitted data over Bluetooth to an off-board computer for real-time monitoring and data recording. The FSM coordinated stimulation and exoskeletal constraints to enable functions, selected with a wireless finger switch user interface, for standing up, standing, stepping, or sitting down. In the stepping function, the FSM used a sensor-based gait event detector to determine transitions between gait phases of double stance, early swing, late swing, and weight acceptance. Results The HNP restored stepping in three individuals with motor complete paralysis due to SCI. The controller appropriately coordinated stimulation and exoskeletal constraints using the sensor-based FSM for subjects with different stimulation systems. The average range of motion at hip and knee joints during walking were 8.5°–20.8° and 14.0°–43.6°, respectively. Walking speeds varied from 0.03 to 0.06 m/s, and cadences from 10 to 20 steps/min. Conclusions A self-contained muscle-driven exoskeleton was a feasible intervention to restore stepping in individuals with paraplegia due to SCI. The untethered hybrid system was capable of adjusting to different individuals’ needs to appropriately coordinate exoskeletal constraints with muscle activation using a sensor-driven FSM for stepping. Further improvements for out-of-the-laboratory use should include implantation of plantar flexor muscles to improve walking speed and power assist as needed at the hips and knees to maintain walking as muscles fatigue.

18 Healthy volunteers were involved and the effect of functional neuromuscular electrical stimulation, which causes flexion of the hand on the corticospinal excitability during motor imaging and resting state, was investigated in this study. It was shown that the combined action of functional electrical stimulation and the kinesthetic motor imagery leads to an increase of the amplitude of motor evoked potentials, caused by a single-pulse transcranial magnetic stimulation. At the same time, in the state of motor rest, this effect was not obtained. Since a change in corticospinal excitability at the cortical level may affect the processes of plastic reorganization necessary for the restoration of motor functions after strokes and other neurotraumas, the results of this work have a direct practical potential. In particular, the possibility of creating effective training complexes for the motor recovery based on motor imagery brain-computer interfaces with functional neuromuscular stimulation as a sensorimotor feedback is discussed. Rehabilitation with the use of such training complexes will help to elucidate the mechanisms of motor recovery, which are based on the phenomena of neuroplasticity due to changes in the excitability of neurons of the sensorimotor cortex. [ABSTRACT FROM AUTHOR]

This study systematically explored the potential of applying feedback control of functional neuromuscular stimulation (FNS) for stabilizing various erect and leaning standing postures after spinal cord injury (SCI). Perturbations ranging from 2 to 6% body weight were applied to two subjects with motor complete thoracic level SCI who were proficient at standing with implanted multichannel neural stimulators to activate the ankle, knee, hip and trunk muscles. The subjects stood with four different postures: erect, forward, forward-right and forward-left. Repeatable and controlled perturbations were applied in the forward, backward, rightward and leftward directions by linear actuators pulling on ropes attached to the subjects via a belt worn just above the waist. Upper extremity (UE) forces exerted on a stationary walker were measured with load cells attached to the handles. A feedback controller based on center of pressure (CoP) varied the stimulation levels to the otherwise paralyzed muscles so as to resist the effects of the perturbations. The effect of the feedback controller was compared to the case where only open-loop baseline stimulation was applied. This was done in terms of: (a) maximum resultant UE force exerted by the subjects on the walker, (b) maximum resultant CoP overshoot and (c) CoP root-mean-square deviation (RMSD). Feedback control resulted in significant reductions in the mean values of the majority of outcome values compared to baseline open-loop stimulation. Maximum resultant UE force was reduced by as much as 50% in one of the postures for one of the subjects. RMSD and maximum CoPs were reduced by as much as 75 and 70%, respectively, with feedback control. These results indicate that feedback control can be used to reject destabilizing disturbances in individuals with SCI using FNS not only for erect postures but also for leaning postures typically adopted during reaching while attempting various activities of daily living. [ABSTRACT FROM AUTHOR]

Background: Implanted motor system neuroprostheses can be effective at increasing personal mobility of persons paralyzed by spinal cord injuries. However, currently available neural stimulation systems for standing employ patterns of constant activation and are unreactive to changing postural demands.Methods: In this work, we developed a closed-loop controller for detecting forward-directed body disturbances and initiating a stabilizing step in a person with spinal cord injury. Forward-directed pulls at the waist were detected with three body-mounted triaxial accelerometers. A finite state machine was designed and tested to trigger a postural response and apply stimulation to appropriate muscles so as to produce a protective step when the simplified jerk signal exceeded predetermined thresholds.Results: The controller effectively initiated steps for all perturbations with magnitude between 10 and 17.5 s body weight, and initiated a postural response with occasional steps at 5% body weight. For perturbations at 15 and 17.5% body weight, the dynamic responses of the subject exhibited very similar component time periods when compared with able-bodied subjects undergoing similar postural perturbations. Additionally, the reactive step occurred faster for stronger perturbations than for weaker ones (p < .005, unequal varience t-test.) CONCLUSIONS: This research marks progress towards a controller which can improve the safety and independence of persons with spinal cord injury using implanted neuroprostheses for standing. [ABSTRACT FROM AUTHOR]

Background: Functional neuromuscular stimulation, lower limb orthosis, powered lower limb exoskeleton, and hybrid neuroprosthesis (HNP) technologies can restore stepping in individuals with paraplegia due to spinal cord injury (SCI). However, a self-contained muscle-driven controllable exoskeleton approach based on an implanted neural stimulator to restore walking has not been previously demonstrated, which could potentially result in system use outside the laboratory and viable for long term use or clinical testing. In this work, we designed and evaluated an untethered muscle-driven controllable exoskeleton to restore stepping in three individuals with paralysis from SCI.Methods: The self-contained HNP combined neural stimulation to activate the paralyzed muscles and generate joint torques for limb movements with a controllable lower limb exoskeleton to stabilize and support the user. An onboard controller processed exoskeleton sensor signals, determined appropriate exoskeletal constraints and stimulation commands for a finite state machine (FSM), and transmitted data over Bluetooth to an off-board computer for real-time monitoring and data recording. The FSM coordinated stimulation and exoskeletal constraints to enable functions, selected with a wireless finger switch user interface, for standing up, standing, stepping, or sitting down. In the stepping function, the FSM used a sensor-based gait event detector to determine transitions between gait phases of double stance, early swing, late swing, and weight acceptance.Results: The HNP restored stepping in three individuals with motor complete paralysis due to SCI. The controller appropriately coordinated stimulation and exoskeletal constraints using the sensor-based FSM for subjects with different stimulation systems. The average range of motion at hip and knee joints during walking were 8.5°-20.8° and 14.0°-43.6°, respectively. Walking speeds varied from 0.03 to 0.06 m/s, and cadences from 10 to 20 steps/min.Conclusions: A self-contained muscle-driven exoskeleton was a feasible intervention to restore stepping in individuals with paraplegia due to SCI. The untethered hybrid system was capable of adjusting to different individuals' needs to appropriately coordinate exoskeletal constraints with muscle activation using a sensor-driven FSM for stepping. Further improvements for out-of-the-laboratory use should include implantation of plantar flexor muscles to improve walking speed and power assist as needed at the hips and knees to maintain walking as muscles fatigue. [ABSTRACT FROM AUTHOR]

This paper reviews the field of feedback control for neuroprosthesis systems that restore advanced standing function to individuals with spinal cord injury. Investigations into closed-loop control of standing by functional neuromuscular stimulation (FNS) have spanned three decades. The ultimate goal for FNS standing control systems is to facilitate hands free standing and enabling the user to perform manual functions at self-selected leaning positions. However, most clinical systems for home usage currently only provide basic upright standing using preprogrammed stimulation patterns. To date, online modulation of stimulation to produce advanced standing functions such as balance against postural disturbances or the ability to assume leaning postures have been limited to simulation and laboratory investigations. While great technological advances have been made in biomechanical sensing and interfaces for neuromuscular stimulation, further progress is still required for finer motor control by FNS. Another major challenge is the development of sophisticated control schemes that produce the necessary postural adjustments, adapt against accelerating muscle fatigue, and consider volitional actions of the intact upper-body of the user. Model-based development for novel control schemes are proven and sensible approaches to prototype and test the basic operating efficacy of potentially complex and multi-faceted control systems. The major considerations for further innovation of such systems are summarized in this paper prior to describing the evolution of closed-loop FNS control of standing from previous works. Finally, necessary emerging technologies to for implementing FNS feedback control systems for standing are identified. These technological advancements include novel electrodes that more completely and selectively activate paralyzed musculature and implantable sensors and stimulation modules for flexible neuroprosthesis system deployment. [ABSTRACT FROM AUTHOR]

Spinal cord injury (SCI) can cause paralysis of trunk and hip musculature that negatively impacts seated balance and ability to lean away from an upright posture and interact fully with the environment. Constant levels of electrical stimulation of peripheral nerves can activate typically paralyzed muscles and aid in maintaining a single upright seated posture. However, in the absence of a feedback controller, such seated postures and leaning motions are inherently unstable and unable to respond to perturbations. Three individuals with motor complete SCI who had previously received a neuroprosthesis capable of activating the hip and trunk musculature volunteered for this study. Subject-specific muscle synergies were identified through system identification of the lumbar moments produced via neural stimulation. Synergy-based calculations determined the real-time stimulation parameters required to assume leaning postures. When combined with a proportional, integral, derivative (PID) feedback controller and an accelerometer to infer trunk orientation, all individuals were able to assume non-erect postures of 30-40° flexion and 15° lateral bending. Leaning postures increased forward reaching capabilities by 10.2, 46.7, and 16 cm respectively for each subject when compared with no stimulation. Additionally, the leaning controllers were able to resist perturbations of up to 90 N, and all subjects perceived the leaning postures as moderately to very stable. Implementation of leaning controllers for neuroprostheses have the potential of expanding workspaces, increasing independence, and facilitating activities of daily living for individuals with paralysis., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Friederich, Lombardo, Foglyano, Audu and Triolo.)

The development of a sensor that can measure balance during quiet standing and predict stepping response in the event of perturbation has many clinically relevant applica- tions, including closed-loop control of a neuroprothesis for standing. This study investigated the feasibility of an algorithm that can predict in real-time when an able-bodied individual who is quietly standing will have to make a step to compensate for an external perturbation. Anterior and posterior perturbations were performed on 16 able-bodied subjects using a pul- ley system with a dropped weight. A linear relationship was found between the peak center of pressure (COP) velocity and the peak COP displacement caused by the perturbation. This result suggests that one can predict when a person will have to make a step based on COP velocity measurements alone. Another important feature of this finding is that the peak COP velocity occurs considerably before the peak COP displacement. As a result, one can predict if a subject will have to make a step in response to a perturbation sufficiently ahead of the time when the subject is actually forced to make the step. The proposed instability detection algorithm will be implemented in a sensor system using insole sheets in shoes with minitur- ized pressure sensors by which the COPv can be continuously measured. The sensor system will be integrated in a closed-loop feedback system with a neuroprosthesis for standing in the near future.

In this simulation study, we present and examine methods to develop a feedback controller for a neuroprosthesis that restores forward and side leaning function during standing following complete thoracic-level spinal cord injury. Achieving leaning postures away from erect stance with functional neuromuscular stimulation (FNS) would allow users to extend their reaching capabilities. Utilizing a 3-D computer model of human stance, an FNS control system based on total-body center of mass (CoM) kinematics (position, acceleration) is developed and tested in simulation. CoM kinematics drive an artificial neural network to modulate muscle excitations and reduce the upper extremity loading, presumably against a walker or similar support surface, required to resist the effects of postural perturbations. Furthermore, a novel method to robustly estimate the feedback kinematics for standing applications is also presented while assuming 3-D accelerometer signals at locations consistent with a proposed implantable networked neuroprosthesis system. For shifting and balance at leaning postures, respectively, center of mass position and acceleration could be approximated to within 20% of the maximum value, with strong correlations (R > 0.9) between values estimated by the proposed method and the true values derived from model dynamics. When utilizing the estimated feedback kinematics for FNS control, standing performance in terms of maximum upper extremity loading was still significantly reduced (p < 0.001) compared to conventionally applying constant and maximal stimulation. In the future, these simulation-based methods will be employed to develop experimental approaches for restoring leaning standing function by FNS. [ABSTRACT FROM AUTHOR]

Standing up, standing, and walking functions can be restored to people with spinal cord injury by contracting the paralyzed hip, knee, and ankle muscles with electrical stimulation. Restoring these functions using electrical stimulation requires controlled activation to provide coordinated movements. However, the stand-to-sit (STS) maneuver involves eccentric contractions of the quadriceps to control lowering of the body to the seated position, which is difficult to achieve with stimulation alone and presents unique challenges to lower-limb neuroprostheses. In this study, we examined the biomechanics of the STS maneuver in five nondisabled individuals and five users of an implanted neuroprosthesis. Neuroprosthesis users relied heavily on their upper limbs during STS, with peak supporting forces approximately 25% body weight, and exhibited an average vertical acceleration at the impact six times higher than that of the nondisabled subjects (p < 0.001). Sitting with stimulation resulted in impact forces at initial contact with the seating surface averaging 1.4 times body weight and representing an average of twice the impact forces of the nondisabled subjects (p < 0.001). These results indicate a need for additional interventions to better control descent, minimize impact, and gently transition from standing to sitting to achieve a more natural movement and reduce the risk of injury. [ABSTRACT FROM AUTHOR]

BACKGROUND: Functional neuromuscular stimulation (FNS) can restore standing capabilities following spinal cord injury. Feedback control of these systems can optimize performance by reducing the required upper extremity support. However, tuning these control systems can be intensive and clinically inconvenient. OBJECTIVE: This case study investigated a clinical method to efficiently tune feedback gains for a control system utilizing feedback of total body center of mass acceleration to modulate stimulation levels to targeted paralyzed musculature of the lower extremities and trunk. METHODS: Gains for this control system were tuned to minimize the stabilization loading by one arm against internal postural perturbations volitionally-generated during manipulation of an object using the other arm. An algorithm based on a modified form of the Newton-Raphson method was employed to find the optimal feedback gains with lower subject effort than that to determine the original tuning curves. RESULTS: This method accurately (<6.2% error) approximated the optimal gains with 70% fewer manipulations by the subject. CONCLUSIONS: These results suggest that optimal feedback gains for the specific FNS control system can be determined systematically with considerably less effort than heuristic gain tuning. This demonstrates the potential for devising simple, convenient methods for effective system re-tuning during clinical usage. [ABSTRACT FROM AUTHOR]

The ability to negotiate stairs is important for community access and independent mobility but requires more effort and strength than level walking. For this reason, previous attempts to utilize functional neuromuscular stimulation (FNS) to restore stair navigation after spinal cord injury (SCI) have had limited success and are not readily generalizable. Stair descent is particularly challenging because it requires energy absorption via eccentric muscle contractions, a task not easily accomplished with FNS. This article presents the design and initial testing of a hybrid neuroprosthesis with a variable impedance knee mechanism (VIKM-HNP) for stair descent. Using a 16-channel percutaneous FNS system, a muscle activation pattern was synthesized to descend stairs with the VIKM-HNP in a step-by-step fashion. A finite state control system was implemented to deactivate knee extensor stimulation and utilize the VIKM-HNP to absorb energy and regulate descent speed. Feasibility testing was performed on one individual with complete thoracic-level SCI. Stair descent was achieved with maximum upper-limb forces of less than 45% body weight compared with previously reported value of 70% with FNS only. The experiments also provided insight into design requirements for future hybrid systems for stair navigation, the implications of which are discussed. [ABSTRACT FROM AUTHOR]

Spinal cord injury (SCI) can compromise the ability to maintain an erect seated posture. This study examined the feasibility of a sensor-based threshold controller to automatically modulate stimulation to paralyzed hip and trunk extensor muscles to restore upright sitting from forward leaning postures. Forward trunk tilt was estimated from the anterior- posterior component of gravitational acceleration sensed by a sternum-mounted wireless accelerometer. Stimulation increased if trunk tilt exceeded a specified flexion threshold and ceased once upright sitting was resumed. The controller was verified experimentally in five volunteers with SCI and successfully returned all subjects to upright postures from forward leaning positions. Upper-limb effort exerted while returning to erect posture was significantly reduced (to 7.4% +/– 3.7% of body mass) pooled across all volunteers while using the controller compared with using continuous and no stimulation (p < 0.03). Controller response times were consistent among subjects when applied while sitting with (0.30 +/– 0.05 s) or without (0.34 +/– 0.11 s) a backrest. The controller enabled volunteers to lean farther forward (59.7° +/– 16.4°) in wheelchairs without upper-limb effort than with no stimulation. Clinical utility of the system for facilitating reach or preventing falls remains to be determined in future studies. [ABSTRACT FROM AUTHOR]

We used a three-dimensional biomechanical model of human standing to test the feasibility of feed-forward control systems that vary stimulation to paralyzed muscles based on the user’s posture and desire to effect a postural change. The controllers examined were (1) constant baseline stimulation, which represented muscle activation required to maintain erect standing, and (2) posture follower, which varied muscle activation as a function of the location of the projection of whole-body center of mass on the base of support. Posture-dependent control of stimulation demonstrated significant benefits over open-loop stimulation. Posture follower reduced upper-limb (UL) effort by an average of 50% compared with UL effort alone and by an average of 34% compared with baseline stimulation. On the other hand, reduction in UL effort was an average of 32% when using baseline stimulation. Compared with using UL effort alone, both controllers result in more than a 50% reduction in effort. The results of this study indicate that control systems that facilitate user-driven, task-dependent postures can be more effective and efficient than conventional open-loop stimulation. Also, they obviate the need for complicated posture-setting devices such as switches and joysticks. Functional implications include the potential to expand reachable workspace and better preparation for anticipated disturbances that could challenge balance over existing neuroprostheses for standing. [ABSTRACT FROM AUTHOR]

The objectives of this study were to test whether a hybrid neuroprosthesis (HNP) with an exoskeletal variable-constraint hip mechanism (VCHM) combined with a functional neuromuscular stimulation (FNS) controller can maintain upright posture with less upper-limb support and improve gait speed as compared with walking with either an isocentric reciprocating gait orthosis (IRGO) or FNS only. The results show that walking with the HNP significantly reduced forward lean in FNS-only walking and the maximum upper-limb forces by 42% and 19% as compared with the IRGO and FNS-only gait, respectively. Walking speed increased significantly with VCHM as compared with 1:1 reciprocal coupling and by 15% when using the sensor-based FNS controller as compared with HNP with fixed baseline stimulation without the controller active. [ABSTRACT FROM AUTHOR]

Background: Functional neuromuscular stimulation (FNS) restores walking function after paralysis from spinal cord injury via electrical activation of muscles in a coordinated fashion. Combining FNS with a controllable orthosis to create a hybrid neuroprosthesis (HNP) has the potential to extend walking distance and time by mechanically locking the knee joint during stance to allow knee extensor muscle to rest with stimulation turned off. Recent efforts have focused on creating advanced HNPs which couple joint motion (e.g., hip and knee or knee and ankle) to improve joint coordination during swing phase while maintaining a stiff-leg during stance phase. Methods: The goal of this study was to investigate the effects of incorporating stance controlled knee flexion during loading response and pre-swing phases on restored gait. Knee control in the HNP was achieved by a specially designed variable impedance knee mechanism (VIKM). One subject with a T7 level spinal cord injury was enrolled and served as his own control in examining two techniques to restore level over-ground walking: FNS-only (which retained a stiff knee during stance) and VIKM-HNP (which allowed controlled knee motion during stance). The stimulation pattern driving the walking motion remained the same for both techniques; the only difference was that knee extensor stimulation was constant during stance with FNS-only and modulated together with the VIKM to control knee motion during stance with VIKM-HNP. Results: Stance phase knee angle was more natural during VIKM-HNP gait while knee hyperextension persisted during stiff-legged FNS-only walking. During loading response phase, vertical ground reaction force was less impulsive and instantaneous gait speed was increased with VIKM-HNP, suggesting that knee flexion assisted in weight transfer to the leading limb. Enhanced knee flexion during pre-swing phase also aided flexion during swing, especially when response to stimulation was compromised. Conclusions: These results show the potential advantages of incorporating stance controlled knee flexion into a hybrid neuroprosthesis for walking. The addition of such control to FNS driven walking could also enable non-level walking tasks such as uneven terrain, slope navigation and stair descent where controlled knee flexion during weight bearing is critical. [ABSTRACT FROM AUTHOR]

Background: Multi-contact stimulating electrodes are gaining acceptance as a means for interfacing with the peripheral nervous system. These electrodes can potentially activate many independent populations of motor units within a single peripheral nerve, but quantifying their recruitment properties and the overlap in stimulation between contacts is difficult and time consuming. Further, current methods for quantifying overlap between contacts are ambiguous and can lead to suboptimal selective stimulation parameters. This study describes a novel method for optimizing stimulation parameters for multi-contact peripheral stimulating electrodes to produce strong, selective muscle contractions. The method is tested with four-contact spiral nerve-cuff electrodes implanted on bilateral femoral nerves of two individuals with spinal cord injury, but it is designed to be extendable to other electrode technologies with higher densities of contacts. Methods: To optimize selective stimulation parameters for multi-contact electrodes, first, recruitment and overlap are characterized for all contacts within an electrode. Recruitment is measured with the twitch response to single stimulus pulses, and overlap between pairs of contacts is quantified by the deviation in their combined response from linear addition of individual responses. Simple mathematical models are fit to recruitment and overlap data, and a cost function is defined to maximize recruitment and minimize overlap between all contacts. Results: Results are presented for four-contact nerve-cuff electrodes stimulating bilateral femoral nerves of two human subjects with spinal cord injury. Knee extension moments between 11.6 and 43.2 Nm were achieved with selective stimulation through multiple contacts of each nerve-cuff with less than 10% overlap between pairs of contacts. The overlap in stimulation measured in response to selective stimulation parameters was stable at multiple repeated time points after implantation. Conclusions: These results suggest that the method described here can provide an automated means of determining stimulus parameters to achieve strong muscle contractions via selective stimulation through multicontact peripheral nerve electrodes. [ABSTRACT FROM AUTHOR]

This study determined the feasibility and performance of center of mass (COM) acceleration feedback control ofa neuroprosthesis utilizing functional neuromuscular stimulation (FNS) to restore standing balance to a single subject paralyzed by a motor and sensory complete, thoracic-level spinal cord injury. An artificial neural network (ANN) was created to map gain-modulated changes in total body COM acceleration estimated from body-mounted sensors to optimal changes in stimulation required to maintain standing. Feedback gains weresystematically tuned to minimize the upper-limb (UL) loads applied by the subject to an instrumented support device during internally generated postural perturbations produced by volition a reaching and object manipulation. Total body COM acceleration was accurately estimated (>90% variance explained) from 2 three-dimensional (3-D) accelerometers mounted on the pelvis and torso. Compared with constant muscle stimulationemployed clinically, COM acceleration feedback control of stimulation improved standing performance by reducing the UL loading required to resist internal postural disturbances by 27%. This case study suggests that COM acceleration feedback could potentially be advantageous in a standing neuroprosthesis since it can be implemented with only a few feedback parameters and requires minimal instrumentation for comprehensive 3-D control of dynamic standing function. [ABSTRACT FROM AUTHOR]

The article presents a study which investigated the feasibility of lessening the muscle stimulation duty cycle and the upper limb loading to a walking aid in a paraplegia patient using hybrid neuroprosthesis (HNP). It says that a hydraulic stance control knee mechanism (SCKM) and a sensor-based functional neuromuscular stimulation (FNS) were combined. It concludes that HNP could reduce the muscle stimulation and limb loading.

We have developed a set of upper-limb functional tasks to guide the design and test the performance of rehabilitation technologies that restore arm motion in people with high tetraplegia. Our goal was to develop a short set of tasks that would be representative of a much larger set of activities of daily living (ADLs), while also being feasible for a user of a unilateral, implanted functional electrical stimulation (FES) system. To compile this list of tasks, we reviewed existing clinical outcome measures related to arm and hand function and were further informed by surveys of patient desires. We ultimately selected a set of five tasks that captured the most common components of movement seen in ADLs and is therefore highly relevant for assessing FES-restored unilateral arm function in individuals with high cervical spinal cord injury. The tasks are intended to be used when setting design specifications and for evaluating and standardizing rehabilitation technologies under development. While not unique, this set of tasks will provide a common basis for comparing different interventions (e.g., FES, powered orthoses, robotic assistants) and testing different user command interfaces (e.g., sip-and-puff, head joysticks, brain-computer interfaces). [ABSTRACT FROM AUTHOR]

The potential efficacy of total body center of mass (COM) acceleration for feedback control of standing balance by functional neuromuscular stimulation (FNS) following spinal cord injury (SCI) was investigated. COM acceleration may be a viable alternative to conventional joint kinematics because of its rapid responsiveness, focal representation of COM dynamics, and ease of measurement. A computational procedure was developed using an anatomically realistic, three-dimensional, bipedal biomechanical model to determine optimal patterns of muscle excitations to produce targeted effects upon COM acceleration from erect stance. The procedure was verified with electromyographic data collected from standing nondisabled subjects undergoing systematic perturbations. Using 16 muscle groups targeted by existing implantable neuroprostheses, we generated data to train an artificial neural network (ANN)-based controller in simulation. During forward simulations, proportional feedback of COM acceleration drove the ANN to produce muscle excitation patterns countering the effects of applied perturbations. Feedback gains were optimized to minimize upper-limb (UL) loading required to stabilize against disturbances. Compared with the clinical case of maximum constant excitation, the controller reduced UL loading by 43% in resisting external perturbations and by 51% during simulated one-arm reaching. Future work includes performance assessment against expected measurement errors and development of user-specific control systems. [ABSTRACT FROM AUTHOR]

A hydraulic stance control knee mechanism (SCKM) was developed to fully support the knee against flexion during stance and allow uninhibited motion during swing for individuals with paraplegia using functional neuromuscular stimulation (FNS) for gait assistance. The SCKM was optimized for maximum locking torque for body-weight support and minimum resistance when allowing for free knee motion. Ipsilateral and contralateral position and force feedback were used to control the SCKM. Through bench and nondisabled testing, the SCKM was shown to be capable of supporting up to 70 N-m, require no more than 13% of the torque achievable with FNS to facilitate free motion, and responsively and repeatedly unlock under an applied flexion knee torque of up to 49 N-m. Preliminary tests of the SCKM with an individual with paraplegia demonstrated that it could support the body and maintain knee extension during stance without the stimulation of the knee extensor muscles. This was achieved without adversely affecting gait, and knee stability was comparable to gait assisted by knee extensor stimulation during stance. [ABSTRACT FROM AUTHOR]

Background. Electrical stimulation of the upper extremity may reduce impairment in patients following stroke. Stimulation triggered on demand combined with task practice may be an effective means of promoting recovery of function. Objective. The authors investigated the feasibility of using accelerometer-controlled electrical stimulation for the elbow, wrist, and finger extensors to enable functional task practice in patients with chronic hemiparesis. Methods.Following a 4-week baseline, participants received 2 weeks of cyclic stimulation exercise to elbow and forearm extensor muscles, followed by 10 weeks of triggered stimulation to practice functional reaching. Participants were reassessed 12 weeks later as well. Outcome measures were the Action Research Arm Test (ARAT), Modified Ashworth Scale (MAS), Canadian Occupational Performance Measure (COPM), Psychosocial Impact of Assistive Devices Scale (PIADS), and Use of Device Questionnaire (UDQ). Results. Fifteen volunteers who had at least 45° of forward shoulder flexion and could initiate elbow extension and grasp completed the study. The ARAT score improved from 19 to 32 (P = .002); the MAS score for elbow, wrist, and finger flexor spasticity was reduced from 2 each to 1, 0, and 1 (P < .05); the COPM performance and satisfaction scores improved (P = .001); and the PIADS became positive for competence (P = .005), adaptability (P = .008), and self-esteem (P = .008). Gains were maintained 12 weeks later. Conclusions. Accelerometer-triggered electrical stimulation to augment task training for the hemiplegic arm is feasible and may improve functional ability and quality of life which may be maintained 12 weeks after treatment. A randomized trial design is required to evaluate efficacy and cost benefit. [ABSTRACT FROM PUBLISHER]

Previous investigations of feedback control of standing after spinal cord injury (SCI) using functional neuromuscular stimulation (FNS) have primarily targeted individual joints. This study assesses the potential efficacy of comprehensive (trunk, hips, knees, and ankles) joint feedback control against postural disturbances using a bipedal, 3-D computer model of SCI stance. Proportional-derivative feedback drove an artificial neural network trained to produce muscle excitation patterns consistent with maximal joint stiffness values achievable about neutral stance given typical SCI muscle properties. Feedback gains were optimized to minimize upper extremity (UE) loading required to stabilize against disturbances. Compared to the baseline case of maximum constant muscle excitations used clinically, the controller reduced UE loading by 55% in resisting external force perturbations and by 84% during simulated one-arm functional tasks. Performance was most sensitive to inaccurate measurements of ankle plantar/dorsiflexion position and hip ab/adduction velocity feedback. In conclusion, comprehensive joint feedback demonstrates potential to markedly improve FNS standing function. However, alternative control structures capable of effective performance with fewer sensor-based feedback parameters may better facilitate clinical usage. [ABSTRACT FROM AUTHOR]

Study design:Proof of concept study to control a neuroprosthesis for grasping using identification of arm movements from ECoG signals.Objective:To test the feasibility of using electrocorticographic (ECoG) signals as a control method for a neuroprosthesis for grasping.Setting:Acute care hospital, Toronto Western Hospital and spinal cord injury (SCI) rehabilitation centre, Toronto Rehabilitation Institute, Lyndhurst Centre. Both hospitals are located in Toronto, Canada.Methods:Two subjects participated in this study. The first subject had subdural electrodes implanted on the motor cortex for the treatment of essential tremor (ET). ECoG signals were recorded while the subject performed specific arm movements. The second subject had a complete SCI at C6 level (ASIA B score) and was fitted with a neuroprosthesis, capable of identifying arm movements from ECoG signals off-line, for grasping. To operate the neuroprosthesis, subject 2 issued a command that would trigger the release of a randomly selected ECoG signal recorded from subject 1, associated with a particular arm movement. The neuroprosthesis identified which arm movement was performed at the time of recording and used that information to trigger the stimulation sequence. A correct ECoG classification resulted in the neuroprosthesis producing the correct hand function (that is grasp and release).Results:The neuroprosthesis classified ECoG signals correctly delivering the correct stimulation strategy with 94.5% accuracy.Conclusions:The feasibility of using ECoG signals as a control strategy for a neuroprosthesis for grasping was shown. [ABSTRACT FROM AUTHOR]

Abstract-This paper describes the performance of a 16-channel implanted neuroprosthesis for standing and transfers after spinal cord injury including four-contact nerve-cuff electrodes stimulating the femoral nerve for knee extension. Responses of the nerve-cuffs were stable and standing times increased by 600% over time-matched values with a similar eight-channel neuroprosthesis utilizing muscle-based electrodes on vastus lateralis for knee extension. [ABSTRACT FROM AUTHOR]

Abstract: The goal of this preliminary study was to investigate the feasibility of using singular value decomposition (SVD) to eliminate the M-wave from the surface electromyogram (EMG) of an electrically stimulated paretic muscle in order to extract the volitional response. An SVD-based algorithm combining the subspaces method and a subsequent filtering is presented. It was evaluated with EMG signals registered from surface of electrically stimulated muscles with simulated paresis and its performance was compared with a conventional fixed filter. The filtering strategy proposed showed a good performance in static conditions where there were no traces of the M-wave. In dynamic conditions, the SVD-based algorithm was robust but with some remaining M-wave traces. It would be as a consequence of modifications in the data matrix and, therefore, in the subspaces generator columns and the singular values. In general, the fixed filter was very sensitive to input signal disturbances. In all of these conditions there was a greater power reduction for the SVD-based filter than for the fixed filter. [Copyright &y& Elsevier]

Abstract: This study investigated the effects of altering foot placement for two individuals with spinal cord injuries (SCI) that stood using functional neuromuscular stimulation (FNS) as compared to an able-bodied subject group. FNS-assisted standers used parallel bars as needed for support, while the able-bodied group stood hands-free. Three different foot placements were tested: side-by-side, wide, and modified tandem. For SCI subjects, the percentage of body weight loaded on the feet was not greatly affected by foot placement, which potentially could be altered to provide postural benefits during functional tasks. Anterior/posterior (A/P) center of pressure (COP) origins tended to be located more anterior in the base of support for SCI subjects as compared to able-bodied subjects. SCI subjects also tended to have medial/lateral (M/L) COP excursions that were larger than able-bodied subjects. The sacrum appeared to hold some promise as a sensor location for monitoring A/P postural sway, but movements in the M/L direction were inconsistent and will require additional study. General guidelines such as positioning the A/P COP more posterior in the base of support and feedback concerning excessive M/L COP displacements may be useful to improve standing performance for SCI subjects. In addition, the modified tandem placement was an effective alternative for making postural adjustments in one SCI subject who experienced excessive right knee flexion with other foot placements. [Copyright &y& Elsevier]

This paper proposes the use of a controlled assistive device, aimed as a support for the impaired individuals to allow a limited ambulatory function. The aim of the overall project is to develop a simple, portable and economically accessible device that permits the limited movement of the inferior extremities on patients with lumbar spinal cord injuries. The scope of the present investigation is limited to not perform medical investigation direct on patients. For the purpose of testing it is planned to use a mechanical model. As the input control interface it will be used a dataglove for the right hand [ABSTRACT FROM AUTHOR]

A bionic neuron (BION) is an inductively powered, miniature implant developed for functional electric stimulation (FES) to reanimate paralyzed limbs. This paper investigates the possibility of reusing the BION antenna coil as a magnetic sensor to provide meaningful posture information for feedback control of FES. A variety of techniques have been developed to model and cancel nonideal effects caused by the shapes of the internal and external coils, ferrite material, and electronic connections. Field warping has been employed to both amplitude and direction to achieve more accurate description of the dipole magnetic field generated by external coils suitable for generating a reference magnetic frame in the environment of a wheelchair. Models of the transmitting coil and the receiving BION coil were validated against experimental data, providing a solid foundation for implementing a sensor system. Based on the established model, a magnetic sensing system combined with customized microelectro-mechanical systems (MEMS) accelerometer has been designed and tested as a prototype on the bench. The sensor output can be employed to compute 6-D position and orientation. A two-step algorithm integrated with multiple error-cancelling techniques demonstrated sufficient accuracy in bench tests to appear promising for control of reach-and-grasp tasks. A sensor fusion step is proposed to estimate the position and orientation of a limb segment using data from multiple implants in muscles, where they will also function as neuromuscular stimulators to produce the movements to be controlled. [ABSTRACT FROM AUTHOR]

Purpose: Purpose one was to characterize the consistency of intra-limb hip/knee (H/K) coordination according to a measure of average coefficient of correspondence (ACC) across strides. Purpose two was to investigate H/K ACC validity and ability to discriminate pre-/post-treatment change in stroke survivors. Methods: Five healthy controls and 32 chronic (>12 mos) stroke survivors were enrolled, and H/K ACC was calculated for both groups. Comparison between controls and stroke was made using the Mann-Whitney Test. Convergent validity of H/K ACC was tested using the Pearson Correlation model with gait speed and the 6 min Walk Test (6MWT). Stroke survivors were randomized to either: (1) gait training with functional neuromuscular stimulation (FNS) using intramuscular (IM) electrodes or (2) gait training without FNS. Both groups had treatment 1.5 h/day, 5 days/week, for 12 weeks, including .5 h coordination exercise, .5 h body weight supported treadmill training (BWSTT), and .5 h over ground gait training. The FNS-IM group used FNS-IM for all treatment components; the No-FNS group did not. Pre-/post-treatment comparisons were made using ANOVA. Results: H/K ACC detected a significant difference between controls versus stroke involved limb (p=.0001) and controls versus stroke uninvolved limb (p=.042). The H/K ACC measure was well-correlated with gait speed (r=.70) and 6MWT (r=.69). H/K ACC showed a significant treatment response to FNS-IM (p=.003), but not No-FNS (p=.747). Conclusions: H/K ACC sensitively discriminated between controls versus stroke involved or uninvolved limbs. H/K ACC was valid, with significant correlations with both walking speed and 6MWT. FNS-IM produced a significant gain in H/K ACC, and No-FNS did not. [ABSTRACT FROM AUTHOR]

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Persistent gait deficits after stroke can cause falls, elevated energy cost and poor endurance. Coordination impairment is an underlying cause of gait deficits. Few efficacious interventions have been described that have targeted and measured restoration of coordinated gait components. Neuromuscular electrical stimulation can provide the critical gait practice characteristic of close-to-normal movements, by electrically inducing muscle contractions and coordinated movements that are not possible under volitional effort. Two-channel, surface neuromuscular electrical stimulation can be synchronized with phases of gait and can provide faster, more symmetrical neuromuscular electrical stimulation-assisted gait than gait with no neuromuscular electrical stimulation. Difficulties encountered during the use of surface neuromuscular electrical stimulation for gait training led to the development of neuromuscular electrical stimulation with implanted technologies. Implanted electrodes and/or stimulators proved to be feasible for gait training in stroke survivors. Gait training with a multichannel neuromuscular electrical stimulation system with implanted electrodes proved more advantageous than gait training without neuromuscular electrical stimulation, according to measures of volitional coordinated gait components (neuromuscular electrical stimulation deactivated). [ABSTRACT FROM AUTHOR]

Twelve moderately to severely involved chronic stroke survivors (>12 mo) were randomized to one of two treatments: robotics and motor learning (ROB-ML) or functional neuromuscular stimulation and motor learning (FNS-ML). Treatment was 5 h/d, 5 d/wk for 12 wk. ROB-ML group had 1.5 h per session devoted to robotics shoulder and elbow (S/E) training. FNSML had 1.5 h per session devoted to functional neuromuscular stimulation (surface electrodes) for wrist and hand (W/H) flexors/extensors. The primary outcome measure was the functional measure Arm Motor Ability Test (AMAT). Secondary measures were AMAT-S/E and AMAT-W/H, Fugl-Meyer (FM) upper-limb coordination, and the motor control measures of target accuracy (TA) and smoothness of movement (SM). ROB-ML produced significant gains in AMAT, AMAT-S/E, FM upper-limb coordination, TA, and SM. FNS-ML produced significant gains in AMAT-W/H and FM upper-limb coordination. [ABSTRACT FROM AUTHOR]

Objective.– Development of upper limb functional surgery in tetraplegics in the last 50 years.Methods.– The literature review relating to the years 1950–2002 was carried out with 3 data bases: Medline, Pascal, Embase. This review also involved a thorough study of non-indexed references.Results.– A large number of surgical procedures are described. Two priorities are stressed by the authors: safety of these procedures and duration of postoperative immobilization.Conclusion.– This review of literature shows that the prospects for restoring upper limb function in tetraplegics are greater than ever, offering a larger number of patients the possibility to increase their independence in daily life. Functional surgery remains, nevertheless, demanding in terms of length of immobilization and presupposes requiring a multidisciplinary approach requiring rehabilitation teams to be up to date with surgical procedures. [Copyright &y& Elsevier]

A Functional Neuromuscular Stimulation (FNS) system was developed to restore the motor function of people with central nervous system disorders. An FNS articular angle control system with an Inverse Dynamics Model (IDM) tuned by a neural network was proposed. The system was designed to control the elbow joint angles by learning the characteristics of the neuromuscular system of controlled limbs. Three kinds of control schemes using the IDM were proposed. In a simulation experiment, the system was able to learn the abnormal characteristics of a limb and any changes in these characteristics, and then allow for better control of the limb. The results of experiments using human participants showed that the system had ability to control both normal and paralysed limbs. [ABSTRACT FROM AUTHOR]

The ability to produce various force patterns at the ankle by microstimulation of the gray matter of the spinal cord was investigated in spinalized frogs. We evaluated the recruitment properties of individual spinal sites and found that forces increase linearly with activation level in the low-force range studied, while the structure of the force pattern remains invariant. We also measured the responses produced by coactivation of two spinal sites activated at two pairs of stimulation levels. Responses were measured at the mechanical level by recording forces at the ankle; and, at the muscular level by recording the electromyographic (EMG) activity of 11 hindlimb muscles. We found that for both pairs of activation, the forces under coactivation were the scaled vectorial summation of the individual responses. At the muscular level, rectified and integrated EMGs also summated during coactivation. Numerous force patterns could, thus, be created by the activation of a few individual sites. These results suggest that microstimulation of the circuitry of the spinal cord (higher order neurons than the motoneurons) holds promise as a new functional neuromuscular stimulation technique for the restoration of multi-joint movements. [ABSTRACT FROM PUBLISHER]