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A Quiet Standing Index for Testing the Postural Sway of Healthy and Diabetic Adults Across a Range of Ages

A quiet standing index is developed for tracking the postural sway of healthy and diabetic adults over a range of ages. Several postural sway features are combined into a single composite feature <i>C</i> that increases with age <i>a</i>. Sway features are ranked based on the <i>r</i> <sup>2</sup>-values of their linear regression models, and the composite feature is a weighted sum of selected sway features with optimal weighting coefficients determined using principal component analysis. A performance index based on both reliability and sensitivity is used to determine the optimal number of features. The features used to form <i>C</i> include power and distance metrics. The quiet standing index is a scalar that compares the composite feature <i>C</i> to a linear regression model <i>f</i>(<i>a</i>) using <i>C</i> <sup>'</sup>(<i>a</i>) = <i>C</i>/<i>f</i>(<i>a</i>). For a motionless subject, <i>C</i> <sup>'</sup> = 0, and when the composite feature exactly matches the healthy control (HC) model, <i>C</i> <sup>'</sup> = 1. Values of <i>C</i> <sup>'</sup> >> 1 represent excessive postural sway and may indicate impaired postural control. Diabetic neurologically intact subjects, nondiabetic peripheral neuropathy subjects (PN), and diabetic PN subjects (DPN) were evaluated. The quiet standing indexes of the PN and DPN groups showed statistically significant increases over the HC group. Changes in the quiet standing index over time may be useful in identifying people with impaired balance who may be at an increased risk of falling.