The goal of this project is to develop new control systems to restore standing function and enhance the postural stability of individuals paralyzed by spinal cord injuries (SCI). Systems that provide the ability to stand, alter standing posture, and maintain balance by automatically adjusting stimulation to the paralyzed muscles will be designed, optimized in simulation, and evaluated experimentally in six volunteers with SCI. The project will result in a unique, comprehensive balance control system that extends the capabilities and improves the safety of all currently available standing neuroprostheses.
The first aim i s to design, implement and test "posture-follower" and "regional set-point" control sub- systems. The posture-follower control element will automatically alter stimulation as users vary their standing postures about the nominal erect position by simply pulling or pushing against a walker. This will ensure that the optimal stimulation to support the body is applied continuously as the center of mass is smoothly relocated to a new location. The regional set-point control element will automatically adjust stimulation to resist disturbances and maintain balance based on joint angle position and center of mass acceleration. This sub-system will be optimized to span the entire base of support and sustain the desired posture defined by the posture-follower. These new control elements will be designed and evaluated individually in simulation, followed by laboratory demonstration and clinical assessment in volunteers with SCI. The sub-systems will then be integrated and compared to constant activation of the paralyzed muscles. The resulting controller should facilitate standing reach and other functional activities of daily living, require less upper extremity effort to maintain balance, resist larger applied perturbations, and be perceived as easier to use than conventional methods of standing. The second specific aim is to develop the capability to execute a "reactive step". This new control element will automatically change foot position to expand the base of support sufficiently to remain standing in response to large, destabilizing disturbances. Work will begin by fully characterizing the electrically-induced flexion withdrawal reflex and evaluating its potential for generating a rapid change in foot placement. These data will be incorporated into computer simulations to identify an appropriate trigger and optimize patterns of stimulation to generate reproducible stepping motion. The resulting sub-system will take action if the applied perturbations exceed those effectively resisted by the set-point controller, and thus avoid impending falls. Effectiveness will be fully assessed in simulation and laboratory experiments involving application of repeatable external perturbations. Finally, all three sub-systems will be integrated into a comprehensive balance control system and thoroughly assessed with recipients of advanced surgically-implanted 16-channel stimulators.

Public Health Relevance

This project will determine the feasibility of a new comprehensive postural control system for implanted neuroprostheses that restores functional standing to individuals with spinal cord injuries (SCI). All existing systems for standing after SCI rely on continuous stimulation of the paralyzed muscles and restrict users to a single, pre-defined posture. We will apply advanced biomechanical modeling and computer simulation techniques to develop new control elements that a) allow users to shift position away from the nominal upright position, b) maintain the user- specified posture by automatically adjusting stimulation based on joint angle and center of mass acceleration, and c) initiate a reactive step to remain upright when challenged by large destabilizing disturbances that might otherwise cause a fall. Performance of the resulting control system will be determined experimentally in six volunteers with motor complete SCI. The outcome will define new interventions that provide the ability to assume task-dependent postures, automatically maintain standing balance, and enhance the safety of implanted standing neuroprostheses.

National Institute of Health (NIH)
Research Project (R01)
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Special Emphasis Panel (ZRG1)
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Ludwig, Kip A
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Case Western Reserve University
Schools of Medicine
United States
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Audu, Musa L; Gartman, Steven J; Nataraj, Raviraj et al. (2014) Posture-dependent control of stimulation in standing neuroprosthesis: simulation feasibility study. J Rehabil Res Dev 51:481-96
Nataraj, Raviraj; Audu, Musa L; Triolo, Ronald J (2013) Center of mass acceleration feedback control of standing balance by functional neuromuscular stimulation against external postural perturbations. IEEE Trans Biomed Eng 60:10-9
Nataraj, Raviraj; Audu, Musa L; Kirsch, Robert F et al. (2012) Trunk acceleration for neuroprosthetic control of standing: a pilot study. J Appl Biomech 28:85-92
Audu, Musa L; Nataraj, Raviraj; Gartman, Steven J et al. (2011) Posture shifting after spinal cord injury using functional neuromuscular stimulation--a computer simulation study. J Biomech 44:1639-45
Triolo, Ronald J; Boggs, Lisa; Miller, Michael E et al. (2009) Implanted electrical stimulation of the trunk for seated postural stability and function after cervical spinal cord injury: a single case study. Arch Phys Med Rehabil 90:340-7
Gustafson, Kenneth J; Pinault, Gilles C J; Neville, Jennifer J et al. (2009) Fascicular anatomy of human femoral nerve: implications for neural prostheses using nerve cuff electrodes. J Rehabil Res Dev 46:973-84
Lambrecht, Joris M; Audu, Musa L; Triolo, Ronald J et al. (2009) Musculoskeletal model of trunk and hips for development of seated-posture-control neuroprosthesis. J Rehabil Res Dev 46:515-28
Gartman, Steven J; Audu, Musa L; Kirsch, Robert F et al. (2008) Selection of optimal muscle set for 16-channel standing neuroprosthesis. J Rehabil Res Dev 45:1007-17
Mushahwar, Vivian K; Jacobs, Patrick L; Normann, Richard A et al. (2007) New functional electrical stimulation approaches to standing and walking. J Neural Eng 4:S181-97
Heilman, Benjamin P; Audu, Musa L; Kirsch, Robert F et al. (2006) Selection of an optimal muscle set for a 16-channel standing neuroprosthesis using a human musculoskeletal model. J Rehabil Res Dev 43:273-86

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