Development of an acceleration based fall risk detector

Falls in the elderly are a major public health issue because of their
associated injuries, morbidity and mortality rates, social cost and financial
cost. Most falls in older adults are caused by impaired locomotion and balance,
reduced vision and other age related body adaptations like reduced muscle
strength. With the increased life expectancy of the elderly and their more
active lifestyle there is now an emphasis on identifying subjects at risk for
falling.
Currently fall risk assessment is performed using questionnaires and scales
which lack diagnostic accuracy because of their subjectivity. Other methods are
expensive, complicated and laboratory based. Previous studies used
accelerometers for several targets, like gait analysis in which movement
characteristics were derived from the acceleration signals using specific
algorithms. These studies showed promising results.

Because the increasing fall problem, mainly due to an impaired gait and balance
ability, this study will investigate fall risk by detecting fall related
movement characteristics. Based on the promising results using accelerometry
for accurate and objective gait analysis, fall risk will be measured using a
triaxial accelerometer.

At the moment our group is performing a study titled 'identify subjects at risk
for falling using accelerometry*. In this study, fall related movement
characteristics (gait, balance, stumble reaction) are identified in healthy
younger and onder subjects under standardised laboratory circumstances. In this
way, specific characteristics can be selected which are responsible for fall
risk.

The aim of this study is investigating if the acceleration based fall risk
detector can be applied in daily life with target groups.

A first step to field measurement with target group is the measurement of
elderly with a certain fall risk in a simple field condition like a nursing
home.

First fall risk is assessed in elderly using the Tinetti scale (score <24)
which is the gold standard for fall risk assessment . This scale consist of a
gait and balance score. Only subjects who have a fall risk are included for
further measurements.

a. A gait test will be performed to analyze movement parameters. Subjects have
to walk 6 times a 20 meter distance at preferred speed while a small
(56mmx61mmx15mm), light weight (5g) and ambulant accelerometer is attached on
the sacrum with an elastic belt. The accelerometer measures accelerations of
the body in three directions (antero-posterior, media-lateral and
cranial-caudal) with a sample frequency of 100Hz.

b. The balance ability will be tested by performing 4 balance tasks while the
same accelerometer measures the movements of the body. Subjects have to stand
with feet closed on a normal or foam surface while having the eyes open and
closed.

c. The Get Up and Go test is performed: subjects start in sitting position,
have to rise, walk 3m, turn around, walk back and sit again. The time needed to
perform this test is measured.

d. 40 subjects (remaining in Scharweyerveld and Zorgboog) are monitored for one
day to investigate the mobility and more fall related movement parameters. The
accelerometer is attached to the sacrum in the morning. First the other 2
measurements are performed, and then subjects wear the device during the whole
day. The accelerometer is small, light and ambulant which is not interferring
with daily acitivities. Subjects have to keep a diary to note all activities
performed during that day. THis will be used to explain the acceleration
signal. Finally a questionnaire assessing fear of falling (FES-I) is performed.

All acceleration data will be analyzed using specific algorithms programmed in
Matlab(c). Statistical analysis will be performed in SPSS using pearson
correlation to investigate correlations between gait parameters, balance
characteristics, the ability perform the Get Up and Go test and fear of
falling. Pearson correlation will also be used to validate the objective gait
and balance test with the Tinetti scale. Differences in function tests between
elderly at risk (measured in this study) and healthy subjects (measured in a
previous study under lab conditious) will be investigated using ANOVA (p<
0.005).

The questionnaire and the 3 function tests (gait, balance, Get Up and Go test)
takes more or less 45 minutes. For the day measurement, the accelerometer is
attached to the sacrum in the morning and is removed when the subject goes to
bed.

The measurements are performed once, all on one day. Moreover they are
performed at the care center where the subject is living. So the subjects don't
need to travel.

Because balancing, walking, sitting and rising from a chair are activities of
daily life, no additional burden or risk is associated with participation.
Moreover because subjects have to behave like normally during the one day
measurement and because the accelerometer is small, light and ambulant subjects
are not limited in performing daily activities and no additional risk is
associated by performing this test.