Evaluating surface EMG control of motorized wheelchairs for amyotrophic lateral sclerosis patients

Abstract

Background: This study evaluated a novel control method for patients unable to independently control powered wheelchairs. Patients with amyotrophic lateral sclerosis often require a wheelchair but struggle with sufficient hand dexterity required for joystick control making them a population that needs this type of control method.

Methods: The study employed a novel control mechanism, using electromyography surface sensors applied to temporalis muscles able to measure the myoelectric voltage. Pattern and magnitude control of muscle contraction allowed for steering intention recognition and were used to manipulate their power wheelchair joystick. Four patients ages 51 to 69, two female and two male with amyotrophic lateral sclerosis, conducted Wheelchair Skills Test developed by Dalhousie University and were surveyed on the experience's Clinical Global Impression of Change.

Results: Findings showed independent steering was capable for patients without hand function and provided recommendations for improved human-machine interface. All patients demonstrated the ability to engage the system, with varying precision, for driving their wheelchair in a controlled environment.

Conclusions: Three patients in the pilot trial reported the highest score of clinical global impression of change, all of whom had lost independent control of their wheelchair joystick. Patient four retained impaired hand dexterity for joystick control and reported negative impression of change, comparatively. Feedback from the study will be leveraged to improve training outcomes. Trial registration Subjects provided signed informed consent according to the Declaration of Helsinki to enter the study that was approved by the Mayo Clinic Institutional Review Board in Rochester, Minnesota. The study is registered on ClinicalTrials.gov under identifier NCT04800926 as of March 14, 2021 retrospectively registered.

Keywords: Amyotrophic lateral sclerosis; Electromyography; Muscle activation; Temporalis muscles; Wheelchair.

Fig. 1

An overview of the EMG control of motorized wheelchair devices. Pictured is a user utilizing electromyography to control the movement of the joystick via the attachment to the wheelchair device

Fig. 2

An overview of the bilateral input mode for the control system. The process flow chart begins and follows the users input signal to initiate a forward or reverse motion with a clench of both temporalis muscles with either a short or long contraction for a forward or reverse command respectively. The user can then initiate the stopping function, which is the same input as the forward command, or begin a turning motion while maintaining forward motion. A turning motion is initiated by a contraction of the temporalis muscle on the side of intended motion. If a turning motion is chosen it can be stopped with an additional turning command and maintain forward motion. Or for a complete stop, the aforementioned stop function will arrest all motion. Once the stopping motion has occurred the user can guide themselves through the process flow again. The user can also begin mid-flow with a simple left or right input command without moving in a forward or reverse motion

Fig. 3

An overview of the unilateral input mode for the control system. The process flow chart begins at the bulls-eye and follows the users input signal to initiate a forward or reverse motion. The forward command is initiated by a hard contraction of a short duration, while the reverse motion is a hard contraction of a long duration. From here the user can then initiate the stopping function, which is the same input as the forward command, or begin a turning motion while maintaining forward motion. A turning motion is chosen it can be stopped with an additional turning command and maintain a forward motion. Or for a complete stop, the aforementioned stop function will arrest all motion. Once the stopping motion has occurred the user can guide themselves through the process flow again. The user also can begin mid-flow with a simple left or right input command without moving in a forward or reverse motion

Fig. 4

An overview of the signal processing chain. The EMG oscillatory signal input is amplified, rectified, band passed, and then smoothed