Understanding the Physiological Significance of Four Inertial Gait Features in Multiple Sclerosis

Abstract

Gait impairment in multiple sclerosis (MS) can result from muscle weakness, physical fatigue, lack of coordination, and other symptoms. Walking speed, as measured by a number of clinician-administered walking tests, is the primary measure of gait impairment used by clinical researchers, but inertial gait features from body-worn sensors have been proven to add clinical value. This paper seeks to understand and differentiate the physiological significance of four such features with proven value in MS to facilitate adoption by clinical researchers and incorporation in gait monitoring and analysis systems. In addition, this information can be used to select features that might be appropriate in other forms of disability. Two of the four features are computed using the dynamic time warping (DTW) algorithm: The "DTW Score" is based on the usual DTW distance, and the "Warp Score" is based on the warping length. The third feature, based on kernel density estimation (KDE), is the "KDE Peak" value. Finally, the "Causality Index" is based on the phase slope index between inertial signals from different body parts. Relationships between these measures and the aforementioned gait-related symptoms are determined by applying factor analysis to three common, clinical walking outcomes, then correlating the inertial measures as well as walking speed to each extracted factor. Statistically significant differences in correlation coefficients to the three extracted clinical factors support their distinct physiological meaning and suggest they may have complimentary roles in the analysis of MS-related walking disability.

Gait Features and their Relationships to Physiological Attributes of Multiple Sclerosis

“…The strong relationships of the clinical data to speed are intuitive and also confirmed by literature, which show that the 6MWT speed has the significant correlation with cognitive and physical impairment in MS, better than the available inertial features, including the gradient of the STSD [17,99]. The adjusted R 2 for cognitive/concentration corresponding to both σ st and ∆ 6M W T is a little over 50.…”

“…In fact, σ st for most of mild subjects is found comparable to those of control subjects. Previous studies [99,112,114] have shown that MS subjects slow down while completing the 6MWT, which indicates more variations in the STSD values for MS subjects over time. speed, higher/lower STSD, or abnormal ranges for other gait parameters could be encountered due to numerous unknown reasons, including (but not limited to) the fact that the person is a slow walker, his/her mood or general health on the day of the clinical visit, the foot-wear, the walking surface, the motivation behind the walk, etc.…”

“…The physiological significance of our inertial features is identified by quantifying their relationships with four crucial aspects of MS disability, namely, weakness, physical fatigue, balance, and cognitive/concentration, as proposed in [99]. Research has shown that degradation in waling is associated with impaired cognition [100], thus, cognitive/concentration impairment is included.…”

“…• Y ∈ Inertial gait features and 6MWT speed Speed is a common clinical anchor used to measure the progression of MS [99], and has been shown to have strong correlation with the overall disability status captured by the EDSS [99,112]. Therefore, we have included speed in the regression analysis to show that our test measures supplement and add value to the speed-based assessments.…”

“…One feature of KDE, its peak value, is shown to have statistically strong and significant relationships with clinical sub-scores capturing balance and weakness disability in MS. The work presented in this chapter was published in [99,115,116].…”