Platforms, Thematic Posters, and Posters for CSM 2007: PLATFORM PRESENTATIONS: Research Platform Session II: Postural Control: Saturday 1:30-3:00 pm
Purpose/Hypothesis: Of the many causes attributed to the decline in postural stability in older adults, difficulty with sensory integration may play an important role. As a result, older adults may have more difficulty maintaining balance when confronted with a sudden change in sensory inputs. The purpose of this study was to test the ability of healthy older adult subjects to respond to sudden changes in magnitude of optic fow. Number of Subjects: Twenty-five healthy young adults (14 females, mean age = 27 y) and 24 healthy older adults (13 females, mean age = 70 y) completed the study. Materials/Methods: Subjects stood on a Neuro Test posture platform within a full feld of view (FOV) display enclosure. The head sway of each subject was recorded using a Polhemus Fastrak™ electromagnetic tracking system. Subjects performed 3 consecutive trials of viewing 0.4 Hz sinusoidal anterior-posterior (AP) optic fow for 50 s while standing on a fixed, level platform. The optic fow increased from an amplitude of 4 cm to 12 cm at a random time between 22 and 28 s of the trial duration. The AP head sway was sampled at 20 Hz and fltered using a 4th order, zero-phase digital Butterworth lowpass flter with a cutof frequency of 2 Hz. The sway velocity of the sampled, fltered data was computed by taking a first-diference of the discrete AP head sway measurements. The instantaneous power of the head sway velocity was determined by squaring the velocity signal. Average power was calculated (in dB) for five consecutive 5 s intervals by averaging the instantaneous power over the interval, and then taking the logarithm. Of the 5 intervals, 2 intervals were before the transition and 3 intervals were after the transition. A mixed factor repeated measures ANOVA was used to test for the effects of subject group (young and older adult), interval (1 to 5), and trial (1, 2, and 3). Results: During the baseline intervals (1 and 2), older adults generated 3 dB greater sway power than young adults (p = 0.006). After the increase in optic fow amplitude at the onset of interval 3, the sway power increased in both subject groups (p = 0.002). However, the magnitude of the increase depended on the subject group (p = 0.015): sway power increased by 2.5 dB in the older adults, but only by 0.3 dB in young adults. In the older adults, the sway power in interval 4 continued to increase significantly by 3.2 dB during the first 2 trials (p <; 0.01), but leveled of in the third trial. Meanwhile the power did not significantly increase in the young subject group in interval 4. Finally, the sway power did not change significantly from interval 4 to 5 in either group (p = 0.77). Conclusions: Previous studies have documented that older adults are more reliant on visual input for postural control. The results of this study further suggest that older adults have difficulty suppressing the influence of a destabilizing visual perturbation compared with young adults. Clinical Relevance: Sudden changes the environmental context may be a factor predisposing older adults for postural instability.