MATERIALS & METHODS
Patients with clinical manifestations of IC were recruited at the outpatient clinic of Vascular Surgery of the Catharina Hospital, Eindhoven and Maxima Medical Center, Veldhoven/Eindhoven, The Netherlands. Healthy individuals recruited from family or friends of healthcare workers served as controls. All subjects gave written informed consent and all procedures described in this study were approved by the Medical Ethical Committee, Catharina Hospital, Eindhoven.
Patients without any previous history of peripheral arterial occlusive disease (PAOD) presenting with new onset clinical manifestations of IC underwent an ankle-brachial index (ABI) measurement using standard equipment. Patients with values below 0.90 at rest or a drop in value of more than 0.15 after a standard treadmill test were considered eligible. Exclusion criteria included serious cardiopulmonary limitations (NYHA class 3-4), critical limb ischemia or previous lower-limb amputation, use of walking aids, psychiatric instability or other serious comorbidity which possibly limited the patient's walking ability.
Healthy volunteers aged >45 years without a history of PAOD, cardiac or pulmonary disease were included if they were able to walk without any limitations or walking aids. Participants were excluded if an ABI measurement was below 0.90 at rest or decreased more than 0.15 after a standard treadmill test.
Functional impairment and health-related quality of life scores
After consenting to the study specifics, a Dutch validated version of the Walking Impairment Questionnaire (WIQ), 12-item Short Form Physical Functioning Summery (SF-12 PCS) and 12-item Short Form Mental Functioning Summery (SF-12 MCS) were assessed prior to treatment in the IC patients and in controls.22, 23 Evidence based conservative treatment was subsequently started in the IC group. Each patient received cardiovascular risk management including antiplatelet therapy and a statin.
Physical activity monitoring
Dynaport tri-axial seismic accelerometer
Both groups of study participants were asked to wear a tri-axial seismic accelerometer (Dynaport MoveMonitor, McRoberts B.V., The Hague, The Netherlands) during a 1 week time period. The Dynaport MoveMonitor (size 84mm X 50m X 8mm; weight 55 g) contains three orthogonal piezo-capacitive acceleration sensors, each measuring at a sample rate of 100Hz. The accelerometer has a direct current response to the Earth's gravitational field, and used a seismic or a proof mass suspended by a spring structure in a case. The case has a micro USB connection and a rechargeable battery and stores the raw data on a Micro-SD card. The Dynaport MoveMonitor is placed in a belt that is strapped around the waist. It is positioned at the base of the lumbar column just cranial to the buttocks. The Dynaport technology is validated for counting steps, detecting time spent in different activities, activity-related energy expenditure and assessment of reproducibility.18, 21, 24-28
All participants were instructed to correctly wear the Dynaport MoveMonitor for 7 consecutive days. As the device is not waterproof, participants were asked to take off the device when taking a shower or a bath. Furthermore, to achieve better compliance, participants were instructed not to wear the device during sleeping. They were instructed to perform their regular daily activities during this week. Supervised exercise therapy (SET) was initiated after this one week monitoring period in IC patients. SET was provided by a specialised physical therapist in a community-based setting. According to the quality standards and guidelines of the Dutch ClaudicatioNet Network and Royal Dutch Society for Physical Therapy, the physical therapist assessed the pain-free walking distance (PFWD) and maximum walking distance (MWD) at baseline according to a standardised graded treadmill protocol.29, 30
- The daily PA level (measured in METs?min)
- The daily PA level performed in bouts of >10 minutes moderate- or vigorous-intensity PA (measured in METs?min)
- The number and percentage of participants meeting the lower limit of the ACSM recommendation for PA and public health (67 METs?min a day)
- The average daily time spent in different activities (Lying, Standing, Sitting, Walking, Shuffling) and the time spent not wearing the device
- The average daily number and highest number of steps walked in one period (top period of steps)
- The average daily time spent in light-, moderate- or vigorous-intensity activity. Sedentary activity is activity with an intensity of <1.5 METs, light activity is activity with an intensity of 1.5-3 METs, moderate activity is activity with an
intensity of 3-6 METs and vigorous activity is activity with an intensity of 6-9 METs.
Daily checks were made to assure proper use of the device. By definition, the device was worn correctly if it detected at least 20 steps and if it was 'worn' =10 hours and 'not worn' for =5 hours a day. Participants with less than 5 days of correctly wearing the device were arbitrarily excluded from analysis. Daily average outcomes were determined for each participant depending on the number of 'correctly worn days'.
The IC group was divided into two subgroups according to the WIQ score (<0.4 or =0.4) in order to evaluate the hypothesis that IC patients with more functional impairment have a lower daily PA level. The WIQ-score was used because it takes both the patient's effort to walk and his perceived impairment into account, while estimated or treadmill walking distances do not reflect walking distances in daily life.31 A lower WIQ-score reflects higher functional impairment. A cut-off value of 0.4 was arbitrarily chosen to establish even groups.
All analyses were performed using IBM SPSS Statistics Version 21 (SPSS Inc., Chicago, IL, USA). Categorical variables are presented as frequencies with percentages. Nominal variables are depicted as the mean ± standard deviation in case of a normal distribution. Statistical differences between the groups were calculated with a Pearson Chi-Square test for categorical variables, an Independent sample T-test for continuous variables between two groups and a One-Way between-groups ANOVA for continuous variables between more than two groups. In case of significant differences between more than two groups, post-hoc Tukey tests were performed to assess a possible significant difference between groups. A p-value <0.05 was used for statistical significance.