In-home daily walking variability: A marker of mild cognitive impairment

Abstract

Background: Increased cognitive andmotor test-to-test variability are associated with Mild Cognitive Impairment (MCI). Home-based, unobtrusive and continuous assessment of walking speed may provide a means of capturing early changes in the real-world trajectory of activity variance characterizing MCI. We examined whether long-term in-home assessment of walking speed and its variability can distinguish MCI from those who are cognitively intact.Methods: Participants enrolled in the Intelligent Systems for Assessing Aging Change (ISSAC) study, a longitudinal study of unobtrusive in-home technologies to detect cognitive and motor decline in independently living seniors, were defined as MCI or normal at baseline using neuropsychological test data and pre-defined algorithms. Walking speed was assessed using passive infra-red sensors fixed in series on the ceiling of the homes of seniors. The weekly median speed and coefficient of variation (CoV) were analyzed using latent trajectory and mixed effects models. Results:Data from 111 ISAAC subjects living alone (35 with MCI) was acquired for a mean of 271.9 6 175.2 days. Mean cohort age was 84.9 6 4.8 yrs. Latent trajectory models identified 3 and 4 distinct trajectories for median speed and CoV, respectively. MCI was not associated with any of the trajectory patterns of weekly median walking speed, but was more likely to be in the group where CoV was high at baseline and remained high over time (OR 1⁄4 7.0; p 1⁄4 0.03), as opposed to be in the group with lower CoVovertime. The mixed effects model controlling for age and gender confirmed these findings showing that MCI was associated with a high CoVof walking speed (p 1⁄4 0.02) that remained high over time (no interaction of time*MCI). Absolute walking speed over time (i.e., weekly median speed) or speed obtained during annual in-person assessments with a stopwatch over the same approximate two year period were not significantly different between the MCI and cognitively intact groups. Conclusions: Unobtrusive home-based assessment of variability in walking speed provides an indicator of individuals with MCI. These and other real-time measures of function may be used to detect transition phases representing presymptomatic or latent disease leading to dementia and to assess treatment outcomes overtime.