http://www.jneuroengrehab.com/content/9/1/59/abstract
Abstract (provisional)
Background
Clinicians need a practical, objective test of postural control that is sensitive
to mild neurological disease, shows experimental and clinical validity, and has good
test-retest reliability. We developed an instrumented test of postural sway (ISway)
using a body-worn accelerometer to offer an objective and practical measure of postural
control.
Methods
We conducted two separate studies with two groups of subjects. Study I: sensitivity
and experimental concurrent validity. Thirteen subjects with early, untreated Parkinson's
disease (PD) and 12 age-matched control subjects (CTR) were tested in the laboratory,
to compare sway from force-plate COP and inertial sensors. Study II: test-retest reliability
and clinical concurrent validity. A different set of 17 early-to-moderate, treated
PD (tested ON medication), and 17 age-matched CTR subjects were tested in the clinic
to compare clinical balance tests with sway from inertial sensors. For reliability,
the sensor was removed, subjects rested for 30 min, and the protocol was repeated.
Thirteen sway measures (7 time-domain, 5 frequency-domain measures, and JERK) were
computed from the 2D time series acceleration (ACC) data to determine the best metrics
for a clinical balance test.
Results
Both center of pressure (COP) and ACC measures differentiated sway between CTR and
untreated PD. JERK and time-domain measures showed the best test-retest reliability
(JERK ICC was 0.86 in PD and 0.87 in CTR; time-domain measures ICC ranged from 0.55
to 0.84 in PD and from 0.60 to 0.89 in CTR). JERK, all but one time-domain measure,
and one frequency measure were significantly correlated with the clinical postural
stability score (r ranged from 0.50 to 0.63, 0.01 < p < 0.05).
Conclusions
Based on these results, we recommend a subset of the most sensitive, reliable, and
valid ISway measures to characterize posture control in PD: 1) JERK, 2) RMS amplitude
and mean velocity from the time-domain measures, and 3) centroidal frequency as the
best frequency measure, as valid and reliable measures of balance control from ISway.
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