Development of a VR-based treadmill control interface for gait assessment of patients with Parkinson's disease

Abstract

Freezing of gait (FOG) is a commonly observed phenomenon in Parkinson's disease, but its causes and mechanisms are not fully understood. This paper presents the development of a virtual reality (VR)-based body-weight supported treadmill interface (BWSTI) designed and applied to investigate FOG. The BWSTI provides a safe and controlled walking platform which allows investigators to assess gait impairments under various conditions that simulate real life. In order to be able to evoke FOG, our BWSTI employed a novel speed adaptation controller, which allows patients to drive the treadmill speed. Our interface responsively follows the subject's intention of changing walking speed by the combined use of feedback and feedforward controllers. To provide realistic visual stimuli, a three dimensional VR system is interfaced with the speed adaptation controller and synchronously displays realistic visual cues. The VR-based BWSTI was tested with three patients with PD who are known to have FOG. Visual stimuli that might cause FOG were shown to them while the speed adaptation controller adjusted treadmill speed to follow the subjects' intention. Two of the three subjects showed FOG during the treadmill walking.

Fig. 1

System Setup: the body-weight support treadmill interface

Fig. 2

Foot velocity (right-blue, left-red) and pelvic velocity (green) while a subject walks at a constant speed. The foot velocity profile in swing phase resembles the first half period of a sine function.

Fig. 3

Schematic diagram showing distance traveled by foot and pelvis during one step. In a swing phase (from toe-off to heel-strike), the distance traveled by the swing foot (L_foot) along the direction of walking is twice the distance traveled by the pelvis (L_pelv).

Fig. 4

Control structure of the BWSTI

Fig. 5

Communication structure: The motion capture system communicates with treadmill controller at 120 Hz, and the treadmill controller sends speed information to VR system at 60Hz.

Fig. 6

Pelvic movement along the walking direction in a 60 seconds walking trial at three different feedback gains.

Fig. 7

Control command profile during the 60 seconds of walking trial with K_ff =1 and K_fb=0.25: (V_com= V_ff + V_fb)

Fig. 8

Temporal/Spatial Parameters from the three subjects. The upper figures show step time and step length and right figures show velocity and double support time. Three subjects walked through a corridor where a virtual wall blocked their passage about 10 meters from the initial position. The left (subject 1) and middle (subject 2) show FOG phenomena while the right (subject 3) does not.