Clinical Trial Details
— Status: Withdrawn
Administrative data
| NCT number |
NCT00719082 |
| Other study ID # |
CI-IRB-01-7-7-08 |
| Secondary ID |
|
| Status |
Withdrawn |
| Phase |
N/A
|
| First received |
July 17, 2008 |
| Last updated |
January 26, 2016 |
| Start date |
July 2008 |
| Est. completion date |
October 2013 |
Study information
| Verified date |
January 2016 |
| Source |
Carrick Institute for Graduate Studies |
| Contact |
n/a |
| Is FDA regulated |
No |
| Health authority |
United States: Institutional Review Board |
| Study type |
Observational
|
Clinical Trial Summary
Falls are the greatest cause of accidental death in the elderly. There is no normative data
on large groups of geriatric subjects specific to their stability scores obtained by
computerized dynamic posturography (CDP). CDP is the standard test to obtain stability
scores and is utilized as the gold standard in posturographic evaluations and fall
prevention
Hypotheses:
Human stability can be measured by CDP. Increased stability is associated with a lessor
probability of falls. Stability decreases as age increases and a normative data collection
of stability scores in the geriatric population will allow and promote clinical applications
which can be utilized in fall prevention.
Description:
Computerized dynamic posturography outcomes will be obtained on geriatric subjects attending
the September, 2008 AARP meeting in Washington, DC. All subjects will be volunteers. The
outcome measurement will be obtained using computerized dynamic posturography, a standard
diagnostic test of balance function. The subject's balance will be tested using a
three-component force platform (CAPS test) under one sensory condition of the modified
Clinical Test of Sensory Interaction on Balance (mCTSIB), the eyes closed without
perturbation. This condition is chosen as studies have shown it to be the single test that
best correlates with balance impairment and falls. The stability score, already used in
several studies by other authors will be used as the primary outcome measure in this
research. It is defined as 1 minus the ratio between the measured sway during the test
(computed as the major axis of a standard 95% confidence ellipse) and the amount of sway a
normal subject of the same height as the one being tested should be able to sway before
falling (also known as the theoretical maximum sway or the theoretical limit of stability,
calculated using a regression formula based on the subject's height developed by NASA in
1962 and commonly used in all posturographic tests). For convenience, the stability score
will be expressed as a percentage. Its definition makes it a convenient and easy to
understand measure to use as a subject able to stand perfectly still with no sway will have
a score of 100%, whereas one that sways as much as the limit of stability will have a score
of 0%. During each test, the subject's sway will be determined by the force platform and its
related software. The CAPS three-component force platform uses 3 load cells arranged in a
triangle to measure the distribution of the vertical ground reaction force on the platform.
The analog load cell signals are amplified and simultaneously sampled by the platform
electronics using three synchronized individual 24-bit delta-sigma analog to digital
converters sampling at 312 kHz and decimating the samples to a data rate of 64 Hz. The use
of three A/D converters insures that the signals from the 3 load cells are acquired
simultaneously with no timing error. The high sampling rate with the high decimation and low
data rate of the sigma-delta converters eliminates aliasing and provides a resolution of
about 4 parts per million. The digital load cell data will be then sent via a USB connection
to the PC where software uses a calibration matrix determined by the manufacturer to compute
the total vertical force and the two horizontal moments acting on the platform. From these
data, the software will compute the point of application of the vertical force acting on the
platform, commonly referred to as the Center of Pressure (CoP). The location of the CoP
coincides in static conditions with the projection of the subject's Center of Mass (CoM)
onto the platform, and its movement relates to the movements of the subject's CoM (sway).
The determination of the actual sway will require the determination of the instantaneous
location of the CoM via the location and inertial properties of each body segment of the
specific subject being tested. The CAPS test, like all posturographic equipment, uses the
movement of the CoP as an approximation of the sway. Because it is an approximation, and
because for kinetic reasons the CoP moves more than the CoM, the 95% confidence interval of
the CoP motion will be considered. This will allow the CAPS software to compute the ellipse
that represents the location of all of the sway samples collected during the test with 95%
confidence. The major axis of this ellipse will represent the maximum sway of the subject in
any direction during the test and it will be used to compute the stability score. To assess
the accuracy and resolution of the measurement chain, calibrated weights of 75 kg and 100 kg
will be positioned in the center of the force platform (as if it were a subject) and 20 sec
acquisitions will be performed: The accuracy of the weight must fall within the instrument's
factory specifications (+2N). Therefore the accuracy for the position claimed by the
manufacturer of +1 mm for a weight of 75 kg will be accepted as correct as it determination
would have required specialized equipment and software available only to the manufacturer.
It should be noted that the overall accuracy of the position of the CoP given by the
instrument will not be relevant in this study as the motion of the CoP will determine the
sway. The sway measurement error will be estimated considering the fact that during the test
at both weights the dead weight will not move, but the measurement chain will indicate a
''sway'' of less then 0.05 mm (measurement noise), therefore the resolution of the
measurement chain and the sway measurement error will be considered to be 0.05 mm. To verify
the repeatability of the measurement chain, the same type of tests will be repeated two
times. The authors have obtained similar results (within the specified accuracy and
resolution) in another study. Given the sway measurement error, the measurement error in the
stability score will be determined. From the definition of the stability score it is clear
that the least the theoretical limit of stability, the more pronounced the effect of the
sway measurement error will be. As the theoretical limit of stability is computed by using
the formula 0.556height626sin(6.258), the shorter the subject, the more the stability score
is sensitive to the measurement errors. To estimate the stability score measurement error a
subject's height of 1.6 m will be considered. Such a subject would have a theoretical limit
of stability of 191.6 mm. For such a subject, a sway measurement error of 0.05 mm means a
stability score measurement error of 0.05/191.6 or, if the score is expressed in percentage,
of 0.026%. Thus, any changes in the stability score greater than that are a consequence of
the subject's sway and not of measurement errors. A CAPS sit to stand test in which the
subject will be asked to stand on the force platform from a sitting position followed by a
posturography test in the eyes closed stance will be obtained on all subjects. Subjects will
be instructed that they will sit on a chair and then stand up without using their hands or a
structure for support. They then wil be instructed to stand on a computerized force plate
platform without pertubation and close their eyes while data is obtained from the
computerized force plate. The subjects will be given practice sessions so that they will be
familiar with the test prior to the collection of data. The CAPS testing, including the sit
to stand and the eyes closed standing test occurs over 90 sec. We will divide the degree of
sway observed during the first half of the eyes closed standing test (10 seconds) and the
second half of the eyes closed standing test (10 seconds)and obtain ratios. If a subjects
sway increases in the second half of the test in reference to the first half we will call
this a fatigability ratio. When individuals demonstrate less sway in the second half of the
test we will call this an adaptability ratio that we consider might be related to some type
of motor learning.
