James J. Abbas

Neural network control of functional neuromuscular stimulation systems: computer simulation studies

A neural network control system has been designed for the control of cyclic movements in functional neuromuscular stimulation (FNS) systems. The design directly addresses three major problems in FNS control systems: customization of control system parameters for a particular individual, adaptation during operation to account for changes in the musculoskeletal system, and attaining resistance to mechanical disturbances. The control system was implemented by a two-stage neural network that utilizes a combination of adaptive feedforward and feedback control techniques. A new learning algorithm was developed to provide rapid customization and adaptation. The control system was evaluated in a series of studies on a computer simulated musculoskeletal model. The model of electrically stimulated muscle used in the study included nonlinear recruitment, linear dynamics, and multiplicative nonlinear torque-angle and torque-velocity scaling factors. The skeletal model consisted of a one-segment planar system with passive constraints on joint movement. Results of the evaluation have demonstrated that the control system can provide automated customization of the feedforward controller parameters for a given musculoskeletal system. It can account for changes in the musculoskeletal system by adapting the feedforward controller parameters on-line and it can resist the effects of mechanical disturbances. These results suggest that this design may be suitable for the control of FNS systems and other dynamic systems.<<ETX>>

Control of functional neuromuscular stimulation systems for standing and locomotion in paraplegics

The authors adopt a control-systems perspective in reviewing past applications of functional neuromuscular stimulation for providing lower extremity motor function in paralyzed individuals. Specifically, their approach emphasizes direct computer-controlled electrical stimulation of paralyzed muscle rather than triggering reflexes. In experimental settings it provides paralyzed individuals with the ability to do functional tasks while standing, to walk short distances on varying surfaces, to negotiate obstacles, and to climb and descend stairs. >

Experimental evaluation of an adaptive feedforward controller for use in functional neuromuscular stimulation systems

An adaptive feedforward control system has been evaluated for use in functional neuromuscular stimulation (FNS) systems. The control system, which utilizes neural network techniques, was used to generate isometric muscle contractions to track a periodic torque trajectory signal. The evaluation of the control system was performed using percutaneous intramuscular electrodes to stimulate the quadriceps muscles of spinal cord injured adolescents. Results of the evaluation indicate that the control system automatically customized its parameters for controlling isometric muscle torque in a particular muscle and that the parameters were adapted on-line to account for changes in muscle properties due to fatigue. This study demonstrates that this control system may play an important role in the development of practical FNS systems that are capable of automatically adjusting stimulation parameters to fit the needs of a particular individual at a given time.

Real-time interaction between a neuromorphic electronic circuit and the spinal cord

We present a novel demonstration of real-time dynamic interaction between an oscillatory spinal cord (isolated lamprey nervous system) and electronic hardware that mimics the spinal motor pattern generating circuitry. The spinal cord and the neuromorphic circuit were interfaced in unidirectional and bidirectional modes. Bidirectional coupling resulted in stable, persistent oscillations. This experimental platform offers a unique paradigm to examine the intrinsic dynamics of neural circuitry. The neuromorphic analog very large scale integration (aVLSI) design and real-time capabilities of this approach may provide a particularly powerful means of restoring complex neuromotor function using neuroprostheses.

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.

Neuromuscular stimulation therapy after incomplete spinal cord injury promotes recovery of interlimb coordination during locomotion.

The mechanisms underlying the effects of neuromuscular electrical stimulation (NMES) induced repetitive limb movement therapy after incomplete spinal cord injury (iSCI) are unknown. This study establishes the capability of using therapeutic NMES in rodents with iSCI and evaluates its ability to promote recovery of interlimb control during locomotion. Ten adult female Long Evans rats received thoracic spinal contusion injuries (T9; 156 +/- 9.52 Kdyne). 7 days post-recovery, 6/10 animals received NMES therapy for 15 min/day for 5 days, via electrodes implanted bilaterally into hip flexors and extensors. Six intact animals served as controls. Motor function was evaluated using the BBB locomotor scale for the first 6 days and on 14th day post-injury. 3D kinematic analysis of treadmill walking was performed on day 14 post-injury. Rodents receiving NMES therapy exhibited improved interlimb coordination in control of the hip joint, which was the specific NMES target. Symmetry indices improved significantly in the therapy group. Additionally, injured rodents receiving therapy more consistently displayed a high percentage of 1:1 coordinated steps, and more consistently achieved proper hindlimb touchdown timing. These results suggest that NMES techniques could provide an effective therapeutic tool for neuromotor treatment following iSCI.

Longitudinal performance of a surgically implanted neuroprosthesis for lower-extremity exercise, standing, and transfers after spinal cord injury.

OBJECTIVE To investigate the longitudinal performance of a surgically implanted neuroprosthesis for lower-extremity exercise, standing, and transfers after spinal cord injury. DESIGN Case series. SETTING Research or outpatient physical therapy departments of 4 academic hospitals. PARTICIPANTS Subjects (N=15) with thoracic or low cervical level spinal cord injuries who had received the 8-channel neuroprosthesis for exercise and standing. INTERVENTION After completing rehabilitation with the device, the subjects were discharged to unrestricted home use of the system. A series of assessments were performed before discharge and at a follow-up appointment approximately 1 year later. MAIN OUTCOME MEASURES Neuroprosthesis usage, maximum standing time, body weight support, knee strength, knee fatigue index, electrode stability, and component survivability. RESULTS Levels of maximum standing time, body weight support, knee strength, and knee fatigue index were not statistically different from discharge to follow-up (P>.05). Additionally, neuroprosthesis usage was consistent with subjects choosing to use the system on approximately half of the days during each monitoring period. Although the number of hours using the neuroprosthesis remained constant, subjects shifted their usage to more functional standing versus more maintenance exercise, suggesting that the subjects incorporated the neuroprosthesis into their lives. Safety and reliability of the system were demonstrated by electrode stability and a high component survivability rate (>90%). CONCLUSIONS This group of 15 subjects is the largest cohort of implanted lower-extremity neuroprosthetic exercise and standing system users. The safety and efficiency data from this group, and acceptance of the neuroprosthesis as demonstrated by continued usage, indicate that future efforts toward commercialization of a similar device may be warranted.

Sensitivity and versatility of an adaptive system for controlling cyclic movements using functional neuromuscular stimulation

This study evaluated an adaptive control system (the PG/PS control system (see J. J. Abbas and H.J. Chizeck, vol. 42, p. 1117-27, 1995)) that had been designed for generating cyclic movements using functional neuromuscular stimulation (FNS). Extensive simulations using computer-based models indicated that a broad range of control system parameter values performed well across a diverse population of model systems. The bet that manual tuning is not required for each individual makes this control system particularly attractive for implementation in FNS systems outside of research laboratories.

Using Mathematical Models and Advanced Control Systems Techniques to Enhance Neuroprosthesis Function

Systems that use electrical stimulation to activate paralyzed muscles, called “neuroprostheses”, have restored important functional capabilities to many people with neurologic disorders such as spinal cord injury or stroke. However, the clinical benefits derived from neuroprostheses have been limited by the quality of control of posture and movement that has been achieved. Over the past few decades, engineers have used mathematical models and control systems technology to develop functional neuromuscular stimulation (FNS) control systems that show promise in the laboratory, but these have not yet been incorporated into practical solutions for clinical problems. This article briefly reviews several of the complicating factors in controlling FNS systems and describes the potential roles of biomechanical modeling and advanced control system technology. Three important challenges in FNS control systems research and development are identified: 1) to obtain an improved understanding of the biomechanical system that we are trying to control and how it is controlled by the intact neural system, 2) to develop new control system technology with a particular focus on strategies that mimic those used by biologic systems, and 3) to integrate the knowledge and technologies into useful systems that meet the needs of neuroprosthesis users. The outlook for the future includes many interesting problems; yet more importantly, it includes relevant clinical benefits to be gained through the application of biomechanical models and advanced control systems techniques in neuroprostheses.

Using electrical stimulation to control standing posture

Describes strategies that have been used to control standing posture with electrical stimulation and reviews research efforts aimed at improving the performance of stimulation systems.