A patient-controlled functional electrical stimulation system for arm weight relief.

Area of Science:

• Biomedical Engineering
• Rehabilitation Technology
• Neuroscience

Background:

• Stroke survivors often experience upper limb motor impairments, limiting their functional independence.
• Functional Electrical Stimulation (FES) is a promising rehabilitation tool, but its effectiveness can be compromised by muscle fatigue and uncertain activation.
• Existing FES control strategies often lack adaptability to changing physiological conditions.

Purpose of the Study:

• To develop and evaluate a patient-driven control strategy for FES that enhances shoulder abduction during stroke rehabilitation.
• To improve the accuracy and robustness of FES-induced muscle recruitment, particularly under conditions of fatigue.
• To reduce the volitional effort required by patients during FES-assisted movements.

Main Methods:

• A feedback control strategy was implemented, using filtered FES-evoked electromyography (EMG) to adjust muscle recruitment levels.
• User-optimization of filter parameters ensured a linear relationship between controller output and shoulder abduction angle with a good signal-to-noise ratio.
• The auto-tuned recruitment controller (RC) was tested on healthy subjects and compared against direct stimulation (DS) under progressive muscle fatigue.

Main Results:

• The RC demonstrated a more linear relationship between recruitment level and abduction angle (R²=0.93) compared to DS (R²=0.79).
• RC effectively compensated for fatigue, with 0% ± 12 decrease in abduction after 6 minutes, versus 42% ± 14 for DS.
• RC significantly reduced angle generation errors (0.23% ± 5.9) compared to DS (14.6% ± 9.7) and achieved a 78% reduction in volitional EMG effort.

Conclusions:

• The proposed patient-driven FES control strategy offers a robust and adaptable method for improving shoulder abduction in rehabilitation.
• This approach effectively mitigates the effects of muscle fatigue and reduces the user's physical exertion.
• Preliminary results in a stroke patient suggest potential clinical applicability for enhancing motor recovery.