Physical activity of elderly patients with rheumatoid arthritis and healthy individuals: an actigraphy study

Participants and procedures

Participants were RA patients under medical treatment who were scheduled to start
a biologic agent in Gunma University Hospital (Gunma Prefecture, Japan) or Isesaki
Fukushima Hospital (Gunma Prefecture, Japan). They were recruited when they visited
their physicians as outpatients. The eligibility criteria of the RA patients were
the following: (1) they fulfilled the American Rheumatism Association 1987 revised
Criteria for RA 16]; (2) they were not experiencing an acute inflammatory episode; (3) they were 60 years
or older; and (4) they were able to perform basic self-care activities in their home.
Of the 23 patients met the eligibility criteria, two declined to participate because
of scheduling conflicts and one was eliminated who could not wear the accelerometer
in accordance with the instructions, leaving 20 patients as study participants.

The medical information of the RA patients (e.g., disease duration, radiographic findings,
previous operation history, and disease activity) was collected from their medical
charts. A radiographic evaluation of the wrist was classified by Larsen’s grading,
which was divided into six categories based on erosion of the cartilage or bone, narrowing
of the joint space, or destruction of the bony outlines 17], 18]. Disease activity was measured by Disease Activity Score 28-C-reactive protein (DAS28-CRP),
which is calculated by the number of tender and swollen joints (of 28 joints), the
C-reactive protein (CRP) level, and the patient’s self assessment of disease activity
using a 100-mm visual analog scale. The DAS28-CRP is a valid measure of disease activity
in RA patients 19].

Healthy individuals were recruited as controls by bulletin boards and flyers in the
affiliated medical institute. The eligibility criteria of the healthy individuals
were the following: (1) they did not have RA or other collagen diseases; (2) they
were 60 years or older; (3) they were not dependent on analgesics because of chronic
pain; and (4) they were able to perform basic self-care activities in their home.
Twenty-five healthy individuals applied to participate and 23 of these individuals
met the eligibility criteria. One individual declined to participate because of a
scheduling conflict, one individual could not wear an accelerometer in accordance
with the device’s instructions, and one individual lacked data because of device malfunction.
Twenty healthy study participants remained. Medications of the participants remained
unchanged during the study period.

The procedure and materials were approved by the institutional review board of Gunma
University Hospital (Gunma Prefecture, Japan) and Isesaki Fukushima Hospital (Gunma
Prefecture, Japan). All study participants provided written, informed consent. The
study period was from June 2010 to December 2012.

Objective measures of physical activity

The objective physical activity of the participants was evaluated by the Actigraph
Mini-Motionlogger (Ambulatory Monitors Inc., Ardsley, NY, USA), an omnidirectional
accelerometer worn on the wrist. It contains a piezoelectric element with a sensitivity
of 0.01 G/min. Zero-crossing mode was used and acceleration counts were accumulated
for every epoch of 1 min.

All participants were instructed to wear the actigraph on the nondominant wrist for
24 h per day for 6–7 consecutive days. By filling out a daily log time sheet, they
were also instructed to identify their bedtime, wake-up time, and the time that the
device was removed (e.g., during bath time).

Subjective measures of physical function

On the final day of the actigraphic survey, subjective physical function was assessed
by questionnaires; Health Assessment Questionnaire disability index (HAQ-DI), which
is a widely used and validated tool to quantify functional ability in patients with
RA. It was calculated as the mean of the highest score in 8 dimensions: dressing,
rising, eating, walking, hygiene, reach, grip, and usual activity. The scores range
from 0 (i.e., no disability) to 3 (i.e., severe disability) 20]. The Japanese version of the Health Assessment Questionnaire is also reported to
be valid and reliable for measuring the functional status of Japanese RA patients
21].

Health-related quality of life

Health-related quality of life was measured by the Medical Outcomes Study (MOS) 36-item
short-form health survey (SF-36). The SF-36 is a general quality of life questionnaire
that consists of eight dimensions: physical functioning, role-physical, bodily pain,
general health perception, vitality, social functioning, role-emotional, and mental
health. The score ranges from 0 to 100; a higher score indicates a better quality
of life 22]. In clinical tests of validity, the subscales of the SF-36 Japan version were valid
in discriminating between groups with and without a severe physical condition 23].

Data analysis

We defined 12 h between 8:00 am and 8:00 pm as the investigation period. Participants
differed in activities after just getting up and just before bedtime that were influenced
by their life style or home environments (e.g., cooking, bathing, or drinking alcohol).
Therefore, we excluded the hours before 8:00 am and after 8:00 pm from the investigation
period. Data from the actigraphs were analytically filtered to identify nonwearing
periods and days without sufficient wear time by use of the following method. When
an actigraph was not worn, judged by the daily log, or when 10 or more contiguous
minutes of 0 activity count were found, these periods were excluded from the further
analysis 11], 13]. A day with 10 wearing hours or more was defined as a valid day 24]. Only participants who had four valid days or more of monitoring were included in
the analysis 25]. The mean (standard deviation [SD]) of valid days for all participants was 6.0 (0.9).

We extracted three parameters from the actigraphic data based on the method by Wilson
et al. 13], who assessed the physical activity of adolescents with and without chronic pain
by actigraphy. The mean activity count (MAC) was calculated as the average value of
all activity counts per minute during the investigation periods of all valid days.
The peak activity count (PAC) was the highest number of all activity counts during
the investigation periods. The low activity ratio (LAR) was calculated as the proportion
of the numbers less than 40 of all activity counts per minute during the investigation
periods 13].

Statistical analysis

Parameters were compared between RA patients and healthy individuals. The correlations
between each parameter and self-reported measures (i.e., the HAQ-DI and subscales
of SF-36) were investigated. The statistical analysis was calculated using R version
2.13.1 (The R Foundation for Statistical Computing), based on the variables, the variances,
and the distributions: Welch two-sample t test or the Wilcoxon rank sum test for comparing two groups; the Pearson’s product–moment
test or the Spearman’s rank sum test for the correlating variables; the Fisher’s exact
test for testing independence in the contingency tables; and analysis of covariance
(ANCOVA) for modeling continuous and categorical variables. For all analyses, a p
value less than 0.05 was considered significant.