IC‐P‐139: In‐home continuous monitoring of gait speed: A sensitive method for detecting motor slowing associated with smaller brain volumes and dementia risk

Slower walking is common with advanced age, and is associated with loss of independence and increased dementia risk. Single gait speed (SGS) measures are typically obtained only at an annual visit. Continuous in-home monitoring of gait speed (CIHM-GS) derived from hundreds of walking episodes per person may provide a better measure linking real-world motor abilities and brain integrity. 19 dementia-free volunteers (mean MMSE 28.7) enrolled in the Intelligent Systems for Assessing Aging Change study underwent 3T brain MRI. FreeSurfer was used to determine brain, ventricular, and hippocampal volumes. Gait speed (GS) was determined: 1) at the time of the MRI, assessing the number of seconds to walk 9 meters with a stopwatch, and 2) using an in-home assessment system that continuously collected data using passive infra-red motion-activity sensors averaged over a one month period aligned with the volunteer's MRI acquisition. Regression analyses examining MRI volumetric measures adjusted for ICV were performed with the outcome of GS. Mean SGS was 81.7 cm/sec, while CIHM-GS was 76.4 cm/sec (correlation: R2 = 0.27, P = 0.02). Slower CIHM-GS was associated with decreased total brain (R2 = 0.29, P = 0.02), increased ventricular (R2 = 0.28, P = 0.02), and decreased hippocampal (R2 = 0.44, P = 0.002) volumes. SGS measures were not associated with either brain or ventricular volumes, but were associated with hippocampal size (R2 = 0.30, P = 0.02). CIHM-GS was associated with brain (P = 0.02) and CSF (P = 0.02) in two separate step-wise regressions with age, and gender as covariates. In a step-wise regression with hippocampal volume as an outcome, and age, gender, and both SGS, and CIHM-GS as covariates, only CIHM-GS remained related to hippocampal volume (0.002). SGS measures may over-estimate walking abilities in the elderly. Compared with SGS, CIHM-GS measures were associated with smaller global and regional brain volumes, indicators of increased dementia risk. CIHM may provide a more accurate reflection of GS in dementia-free elderly gauging biologically relevant changes in motor performance associated with cognitive decline.