Published on: June 11, 2012
by Tod Neale for MedPage Today:
Passively monitoring how quickly an individual walks in the home may provide clues about the development of mild cognitive impairment, researchers suggested.
Older individuals with mild cognitive impairment were more likely than their cognitively intact counterparts to walk slowly instead of at a moderate or fast speed, according to Hiroko Dodge, PhD, of Oregon Health & Science University in Portland, and colleagues.
In addition, mild cognitive impairment was associated with variations in walking speed, the researchers reported in the June 12 issue of Neurology.
“Although we found a difference in decline in walking speed between the nonamnestic mild cognitive impairment and cognitively intact groups, further in-home studies will be required to translate this finding to clinically relevant ways of identifying those who may develop mild cognitive impairment prospectively,” the authors wrote.
The study included individuals 70 and older (mean age 84) who were living independently and who participated in the Intelligent Systems for Assessing Aging Change (ISAAC) cohort study. The homes of all of the participants were fitted with passive infrared sensors to measure walking speed.
At baseline, there were 54 participants with intact cognition, 31 with nonamnestic mild cognitive impairment, and eight with amnestic mild cognitive impairment. The researchers focused on the individuals with nonamnestic impairment because the sample size was large enough for comparisons. Follow-up lasted 2.6 years.
The researchers defined three groups based on mean walking speed — slow, moderate, and fast. The moderate and fast groups had slight declines in walking speed during the study, whereas the slow group had a more noticeable reduction.
The individuals with nonamnestic mild cognitive impairment were about 9 times more likely to be in the slow group than in the fast and about 5 times more likely to be in the slow group than in the moderate group (P=0.01 for both).
The participants with nonamnestic mild cognitive impairment made up 16.7% of the fast group, 34.6% of the moderate group, and 66.7% of the slow group.
In addition to walking speed, the researchers also used walking speed variability to define groups. The magnitude of walking speed variability was expressed as the coefficient of variation.
Group 1 was characterized by the highest baseline variability, followed by an increase in variability and then sharply declining coefficient of variation. Groups 2 and 3 had relatively stable coefficients of variation during the study and group 4 had the lowest baseline coefficient of variability with a decline over time.
Individuals with nonamnestic mild cognitive impairment were more likely to be in either group 1 or 4, “possibly representing the trajectory of walking speed variability for early- and late-stage mild cognitive impairment, respectively,” according to the authors.
“At the early stage of disease, subjects may begin to develop increasing variability in clinical outcomes such as day-by-day fluctuations in walking speed, balance, functional abilities, mood, or cognitive performance,” they explained. “This phase of increasing variability would be the result of physiologic or functional reserve trying to compensate for the dysfunction associated with the disease.”
“However,” they continued, “once compensatory systems fail or pathologic burdens go beyond the level sustainable by reserve, the variability or short-term fluctuation diminishes because biologic systems lose their ability to preserve premorbid function.”
The researchers acknowledged that the study was limited by the focus on nonamnestic mild cognitive impairment and the nonrandom selection of participants.
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