title: Modified Newton-Raphson method to tune feedback gains of control system for standing by functional neuromuscular stimulation following spinal cord injury.
abstract: 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.
authors: Louis Stokes Veterans Affairs Medical Center, Motion Study Laboratory, Cleveland, OH, USA ; Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA ; Department of Orthopaedics, Case Western Reserve University, Cleveland, OH, USA.
authors: Raviraj
authors: R
authors: Nataraj
authors: Louis Stokes Veterans Affairs Medical Center, Motion Study Laboratory, Cleveland, OH, USA ; Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA ; Department of Orthopaedics, Case Western Reserve University, Cleveland, OH, USA.
authors: Musa L
authors: ML
authors: Audu
authors: Louis Stokes Veterans Affairs Medical Center, Motion Study Laboratory, Cleveland, OH, USA ; Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA ; Department of Orthopaedics, Case Western Reserve University, Cleveland, OH, USA.
authors: Ronald J
authors: RJ
authors: Triolo
keywords: Standing; adaptive algorithm; feedback control system; functional neuromuscular stimulation; spinal cord injury