Evaluation of Gait Phase Detection Delay Compensation Strategies to Control a Gyroscope-Controlled Functional Electrical Stimulation System During Walking

Abstract

Functional electrical stimulation systems are used as neuroprosthetic devices in rehabilitative interventions such as gait training. Stimulator triggers, implemented to control stimulation delivery, range from open- to closed-loop controllers. Finite-state controllers trigger stimulators when specific conditions are met and utilize preset sequences of stimulation. Wearable sensors provide the necessary input to differentiate gait phases during walking and trigger stimulation. However, gait phase detection is associated with inherent system delays. In this study, five stimulator triggers designed to compensate for gait phase detection delays were tested to determine which trigger most accurately delivered stimulation at the desired times of the gait cycle. Motion capture data were collected on seven typically-developing children while walking on an instrumented treadmill. Participants wore one inertial measurement unit on each ankle and gyroscope data were streamed into the gait phase detection algorithm. Five triggers, based on gait phase detection, were used to simulate stimulation to five muscle groups, bilaterally. For each condition, stimulation signals were collected in the motion capture software via analog channels and compared to the desired timing determined by kinematic and kinetic data. Results illustrate that gait phase detection is a viable finite-state control, and appropriate system delay compensations, on average, reduce stimulation delivery delays by 6.7% of the gait cycle.

Keywords: finite-state control; functional electrical stimulation (FES); gait phase detection (GPD).

Figure 1

A representation of trigger timing for each gait phase. Purple, red, and green arrows illustrate the percentage delay added to gait phase onset for T2 (25% gait phase duration), T3 (50% gait phase duration), and T4 (75% gait phase duration), respectively. T2–T4 triggered stimulation (stim) for the upcoming phase. The same trigger condition was applied to all gait phases. T2, 25% gait phase duration delay trigger; T3, 50% gait phase duration delay trigger; T4, 75% gait phase duration delay trigger. LR—Loading Response, MSt—Mid-Stance, TSt—Terminal Stance, PSw—Pre-Swing, ISw—Initial Swing, MSw—Mid-Swing, TSw—Terminal Swing.

Figure 2

Schematic of the comparison between the stimulation signal of the FES system (yellow arrows) and the desired stimulation timing derived from motion capture data (red arrows).

Figure 3

Comparison of desired stimulation timing determined from motion capture data (DESIRED) and the stimulation timing for five finite-state triggers used to control a FES system during walking. T1: Current gait phase-triggered stimulation for upcoming phase (pre-trigger), T2: 25% gait phase duration delay added to pre-trigger, T3: 50% gait phase duration delay added to the pre-trigger, T4: 75% gait phase duration delay added to the pre-trigger, and T5: Current gait phase-triggered stimulation for current phase.