1. Table1. Average Activity Counts
Pilot study to assess the discriminatory properties and reproducibility of the ActiTrac activity monitors. Ms L Houchen1, Dr J Bankart2 and Professor SJ Singh1,3. 1 Pulmonary Rehabilitation Department, Glenfield Hospital, Leicester, U.K.2 Department of Health Sciences, University of Leicester, Leicester, U.K. 3Faculty of Health & Life Sciences, Coventry University, Coventry, U.K.
Introduction Reduced physical activity in COPD is associated with poor prognosis and increased risk of hospitalisation 1-2. The objective monitoring of activity in COPD is therefore of clinical interest and many devices are available. We tested the ActiTrac accelerometers (IM systems, Baltimore, USA) prior to their use in COPD patients. They are easy to use and relatively inexpensive (approx. cost- device: €470, software: €270).
Aims To assess the ActiTrac activity monitors for:
Reproducibility of each monitor over 5 tests, at a given speed
Between monitor reproducibility at a given speed
The ability to discriminate between walking speeds
Table1. Average Activity Counts
Monitor
Speed
Mean (SD)
95% CI
Median (IQR) CV 1
1.78
41.0 (12.1)
26.0 – 56.0
39.0 (21.0)
29.5
3.6
90.0 (15.7)
70.5 – 109.5
88.0 (30.0)
17.4
5.54
128.6 (20.2)
103.6 – 153.6
121.0 (38.0)
15.7 2
25.4 (2.5)
22.3 – 28.5
24.0 (5.0)
9.8
46.0 (1.5)
45.0 – 48.6
47.0 (3.0)
3.3
97.0 (4.2)
91.7 – 102.3
96.0 (8.0)
4.3 3
27.8 (2.4)
24.8 – 30.8
29.0 (4.0)
8.6
57.2 (3.0)
53.5 – 60.9
56.0 (5.0)
5.2
83.8 (11.9)
69.0 – 98.6
79.0 (21.0)
14.3 4
24.2 (0.8)
23.2 – 25.2
24.0 (2.0)
60.4 (2.9)
56.8 – 64.0
60.0 (5.0)
4.8
97.4 (12.5)
81.8 – 113.0
95.0 (21.0)
12.8 5
25.0 (3.0)
21.3 – 28.7
12.0
59.8 (3.8)
55.1 – 64.5
60.0 (8.0)
6.4
106.4 (12.2)
91.3 – 121.5
105.0 (22.0)
11.5
Figure1.
Results Within monitor reproducibility is shown in table1. Monitor 1 had poor reproducibility and was significantly different to the other 4 monitors (p≤0.01), at all speeds. There were no significant differences between monitors 2-5 at each speed (figure2). Kruskal- Wallis analysis indicated that all monitors could distinguish between the 3 walking speeds (p≤0.01).
Method 5 monitors were tested at different times. These were lightweight (34g) devices and were attached to a healthy subject (L.H- Figure1). L.H performed 5, 20-minute walks at 3 different speeds in 5-minute sections (random order). The 3 speeds were chosen from the ESWT: 1.78km/hr (slow), 3.6km/hr (moderate) and 5.54km/hr (fast). Average activity counts (acceleration per minute) were analysed (0-250 threshold).
Conclusions The ActiTrac accelerometers are reproducible in the same wearer on consecutive occasions (p>0.05), with the exception of monitor 1. All monitors could distinguish between the selected walking speeds. The monitors are a simple to use and relatively inexpensive tool to measure activity in patients with COPD.
Slow
Table1. CV= coefficient of variation Speeds:
Moderate
Fast
References1Garcia-Americh et al (2006) Regular physical activity reduces hospital admission and mortality in chronic obstructive pulmonary disease: a population based cohort study. Thorax, 61: Pitta et al (2006) Physical activity and hospitalisation for exacerbation of COPD. Chest, 129: