Hybrid and adaptive control of functional electrical stimulation to correct hemiplegic gait for patients after stroke

Abstract

Introduction: Gait, as a fundamental human movement, necessitates the coordination of muscles across swing and stance phases. Functional electrical stimulation (FES) of the tibialis anterior (TA) has been widely applied to foot drop correction for patients with post-stroke during the swing phase. Although the gastrocnemius (GAS) during the stance phase is also affected, the Functional electrical stimulation of the gastrocnemius received less attention. Methods: To address this limitation, a timing- and intensity-adaptive Functional electrical stimulation control strategy was developed for both the TA and GAS. Each channel incorporates a speed-adaptive (SA) module to control stimulation timing and an iterative learning control (ILC) module to regulate the stimulation intensity. These modules rely on real-time kinematic or kinetic data during the swing or stance phase, respectively. The orthotic effects of the system were evaluated on eight patients with post-stroke foot drop. Gait kinematics and kinetics were assessed under three conditions: no stimulation (NS), Functional electrical stimulation to the ankle dorsiflexor tibialis anterior (SA-ILC DS) and FES to the tibialis anterior and the ankle plantarflexor gastrocnemius (SA-ILC DPS). Results: The ankle plantarflexion angle, the knee flexion angle, and the anterior ground reaction force (AGRF) in the SA-ILC DPS condition were significantly larger than those in the NS and SA-ILC DS conditions (p < 0.05). The maximum dorsiflexion angle during the swing phase in the SA-ILC DPS condition was similar to that in the SA-ILC DS condition, with both being significantly larger than the angle observed in the NS condition (p < 0.05). Furthermore, the angle error and force error relative to the set targets were minimized in the SA-ILC DPS condition. Discussion: The observed improvements can be ascribed to the appropriate stimulation timing and intensity provided by the SA-ILC DPS strategy. This study demonstrates that the hybrid and adaptive control strategy of functional electrical stimulation system offers a significant orthotic effect, and has considerable potential for future clinical application.

Keywords: functional electrical stimulation; hemiplegic gait; hybrid; iterative learning control; stroke.

FIGURE 1

The structure of the FES system.

FIGURE 2

The hybrid and adaptive control strategy of the FES system.

FIGURE 3

(A) ankle angles (mean ± std) and (B) knee angles (mean ± std) during the gait cycle for eight post-stroke subjects at comfortable speed.

FIGURE 4

(A) Maximum ankle dorsiflexion angles during swing phase for 8 subjects after stroke, *Significant difference (p < 0.05). (B) Peak ankle plantarflexion angles at toe-off event for 8 subjects after stroke, *Significant difference (p < 0.05). (C) Maximum knee flexion angles during swing phase for 8 subjects after stroke, *Significant difference (p < 0.05).

FIGURE 5

The error between the actual maximum ankle dorsiflexion during swing phase and the target angle of each successive step when the eight subjects performed FES-assisted treadmill walking in the SA-ILC DPS conditions.

FIGURE 6

(A) The anterior ground reaction force (AGRF) during the gait cycle for eight post-stroke subjects at comfortable speed. (B) The peak AGRF during swing phase for 8 subjects after stroke, *Significant difference (p < 0.05).

FIGURE 7

(A) The error between the ratio of the peak AGRF during the stance phase to the subject’s body weight and the target ratio of each successive step when 8 subjects performed FES-assisted treadmill walking in the SA-ILC DPS condition. (B) The peak AGRF during the stance phase and the target ratio when subject 2 performed FES-assisted treadmill walking in NS, SA-ILC DS, and SA-ILC DPS conditions.