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Research Papers

A Model of the Upper Extremity Using FES for Stroke Rehabilitation

[+] Author and Article Information
Chris T. Freeman, Paul H. Chappell, Paul L. Lewin, Eric Rogers

School of Electronics and Computer Science,  University of Southampton, Highfield, Southampton SO17 1BJ, UK

Ann-Marie Hughes, Jane H. Burridge

School of Health Sciences,  University of Southampton, Highfield, Southampton SO17 1BJ, UK

J Biomech Eng 131(3), 031011 (Jan 07, 2009) (12 pages) doi:10.1115/1.3005332 History: Received February 27, 2008; Revised June 25, 2008; Published January 07, 2009

A model of the upper extremity is developed in which the forearm is constrained to lie in a horizontal plane and electrical stimulation is applied to the triceps muscle. Identification procedures are described to estimate the unknown parameters using tests that can be performed in a short period of time. Examples of identified parameters obtained experimentally are presented for both stroke patients and unimpaired subjects. A discussion concerning the identification’s repeatability, together with results confirming the accuracy of the overall representation, is given. The model has been used during clinical trials in which electrical stimulation is applied to the triceps muscle of a number of stroke patients for the purpose of improving both their performance at reaching tasks and their level of voluntary control over their impaired arm. Its purpose in this context is threefold: Firstly, changes occurring in the levels of stiffness and spasticity in each subject’s arm can be monitored by comparing frictional components of models identified at different times during treatment. Secondly, the model is used to calculate the moments applied during tracking tasks that are due to a patient’s voluntary effort, and it therefore constitutes a useful tool with which to analyze their performance. Thirdly, the model is used to derive the advanced controllers that govern the level of stimulation applied to subjects over the course of the treatment. Details are provided to show how the model is applied in each case, and sample results are shown.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Subject using the robotic workstation to perform a tracking task

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Figure 2

Geometry of the combined human arm and robotic arm system

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Figure 3

Geometry of the constrained two-link human arm model

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Figure 5

Elastic friction function components (a) Fae1(ϑu) and (b) Fae2(ϑf) identified for both stroke patients and unimpaired subjects (subjects A and B and C and D, respectively)

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Figure 6

Viscous friction and elastic friction functions (a) Fae1(ϑu), (b) Fae2(ϑf), (c) Fav1(ϑ̇u), and (d) Fav2(ϑ̇f) for subjects A, B, C, and D

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Figure 7

Combined viscous and elastic friction function components Fa1(ϑu,ϑ̇u) and Fa2(ϑf,ϑ̇f) for subjects (a) A, (b) B, (c) C, and (d) D

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Figure 8

Muscle function, Fma(β,β̇), for subjects (a) A, (b) B, (c) C, and (d) D

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Figure 9

Muscle functions (a) Fma1(β) and (b) Fma2(β̇) for subjects A–D

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Figure 10

Simulation (thick line) and experimental (thin line) results for subjects A (solid line) and B (dashed line) in (a) ϑu and (b) ϑf directions using u(t)=75(1−cos(2πt∕5))

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Figure 13

Experimental data from six trials of a repeated task for subject D using voluntary effort and FES: (a) applied FES pulsewidth, (b) ΔTu, (c) ΔTβ, and (d) approximate voluntary stimulation, vk

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Figure 4

Experimental results from subject D showing (a) stimulation ramp input, u, and recorded elbow torque, (b) deconvolved elbow torque plotted against pulse width with fitted function hIRC(u), and (c) modeled torque g(u,t) and original elbow torque

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Figure 11

Simulation (thick line) and experimental (thin line) results for subjects C (solid line) and D (dashed line) in (a) ϑu and (b) ϑf directions using u(t)=75(1−cos(2πt∕5))

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Figure 12

Moments developed by voluntary action during a reaching task for subject D, (a) about the shoulder and (b) about the elbow, calculated using the identified arm model. The torques necessary to complete the task perfectly are given for subject D and for an unimpaired subject (subject A).

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