Acceleration patterns during the 6-minute walk test

The 6-minute walk test (6MWT) is commonly used in evaluating functional
exercise capacity in various chronic diseases. However, the way patients get to
a certain distance is poorly investigated. Analyzing walking patterns of
patients can be useful in characterizing different pathological states and
functional status. Recently Hausdorff (2007) suggested detrended fluctuation
analyses (DFA) as method to evaluate mobility of patients and elderly with fall
risk.[1] DFA provides insight in long-range correlations in gait by a single
scaling exponent α. An α towards 1.0 indicates healthy long-range, fractal
correlations. On the other hand, an α closer to 0.5, indicating randomness, can
be related to age-related and pathologic alterations in the locomotor control
system. Besides physiological factors α can also be influenced by environmental
factors. When healthy subjects are restricted to walk with a certain step
frequency, time series fluctuations become more uncorrelated and α drops
towards 0.5. [1] Yet when subjects walk fast, α increases toward 1.0. Decrease
in α has been associated with central neurological diseases, such as Parkinson
and Huntington*s disease and gait unsteadiness in the elderly. Although α does
not alter in patients with peripheral limitations, [2] it is not conclusively
known if α can also reflect control processes of other physiological systems.
Therefore we will have a closer look at the fractal dynamics of gait in chronic
obstructive pulmonary disease (COPD) patients during the 6MWT with healthy age
matched subjects as reference. COPD is a highly prevalent chronic lung disease,
characterized by reduced muscle function and pulmonary dysfunction. α may offer
additional information on 6MWT performance that can be used to identify COPD
severity.

Primary objectives:
-Compare the stride-interval correlations (α) of gait in COPD patients with
healthy age matched adults using accelerometers.
-Investigate if this information is clinically useful to distinguish between
GOLD stages 1+2 / 3 / 4.

Secondary objective:
-Explore other methods to characterize walking performance during the 6MWT in
COPD patients with healthy adults as reference.

Case-control study design.

All subjects will be recruited in the morning at ciro. Participants will be
informed both verbally as in written. Subjects will have at least one day time
for reflection before decide if they are willing to participate. The
accelerometer that will be used in this study is the Minimod, McRoberts, The
Hague, The Netherlands (size: 8.5 x 5.0 x 1.0 cm, weight: 70 g). This
accelerometer will be attached to the trunk using an elastic belt.

Study procedure for COPD patients:
All assessments will be integrated in the clinical routine. Patients will be
asked to wear the accelerometer during the 6MWT. The 6MWT will be performed two
times. Only data obtained form the best test (highest distance) will be used
for further analyses. The lung function test, two 6MWT*s and questionnaires
before and after the 6MWT*s used for this study are already part of the
clinical routine. Outcome parameters from these tests as well as date of birth,
gender, weight and height will be taken from their medical recordings.

Study procedure for healthy controls:
Healthy controls will be matched with the COPD population on age, gender,
height and weight, Healthy controls will be asked to walk continuously as far
as possible within six minutes (6MWT). Prior to the 6MWT and immediately after
the test the examiner asks the participant for self-reported dyspnea and
fatigue with a ten point Borg Scale. During the test subjects will wear the
accelerometer. After the first 6MWT, the Forced Expiratory Volume in One Second
(FEV1) and Forced Vital Capacity (FVC) is determined using spirometry. In
addition date of birth, gender, weight and height will be assessed. After these
assessments, controls will be asked to do another 6MWT while wearing the
accelerometer. Also before and after the second 6MWT participants will be asked
to report dyspnea and fatigue. Only data obtained form the best test (highest
distance) will be used for further analyses. The total duration of the study
will be 30 minutes.

Not applicable