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      The Minimal Important Difference in Physical Activity in Patients with COPD

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          Abstract

          Background

          Changes in physical activity (PA) are difficult to interpret because no framework of minimal important difference (MID) exists. We aimed to determine the minimal important difference (MID) in physical activity (PA) in patients with Chronic Obstructive Pulmonary Disease and to clinically validate this MID by evaluating its impact on time to first COPD-related hospitalization.

          Methods

          PA was objectively measured for one week in 74 patients before and after three months of rehabilitation (rehabilitation sample). In addition the intraclass correlation coefficient was measured in 30 patients (test-retest sample), by measuring PA for two consecutive weeks. Daily number of steps was chosen as outcome measurement. Different distribution and anchor based methods were chosen to calculate the MID. Time to first hospitalization due to an exacerbation was compared between patients exceeding the MID and those who did not.

          Results

          Calculation of the MID resulted in 599 (Standard Error of Measurement), 1029 (empirical rule effect size), 1072 (Cohen's effect size) and 1131 (0.5SD) steps.day -1. An anchor based estimation could not be obtained because of the lack of a sufficiently related anchor. The time to the first hospital admission was significantly different between patients exceeding the MID and patients who did not, using the Standard Error of Measurement as cutoff.

          Conclusions

          The MID after pulmonary rehabilitation lies between 600 and 1100 steps.day -1. The clinical importance of this change is supported by a reduced risk for hospital admission in those patients with more than 600 steps improvement.

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          Most cited references 22

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          Interpreting small differences in functional status: the Six Minute Walk test in chronic lung disease patients.

          Functional status measurements are often difficult to interpret because small differences may be statistically significant but not clinically significant. How much does the Six Minute Walk test (6MW) need to differ to signify a noticeable difference in walking ability for patients with chronic obstructive pulmonary disease (COPD)? We studied individuals with stable COPD (n = 112, mean age = 67 yr, mean FEV1 = 975 ml) and estimated the smallest difference in 6MW distances that was associated with a noticeable difference in patients' subjective comparison ratings of their walking ability. We found that the 6MW was significantly correlated with patients' ratings of their walking ability relative to other patients (r = 0.59, 95% confidence interval [CI]: 0.54 to 0.63). Distances needed to differ by 54 m for the average patient to stop rating themselves as "about the same" and start rating themselves as either "a little bit better" or "a little bit worse" (95% CI: 37 to 71 m). We suggest that differences in functional status can be statistically significant but below the threshold at which patients notice a difference in themselves relative to others; an awareness of the smallest difference in walking distance that is noticeable to patients may help clinicians interpret the effectiveness of symptomatic treatments for COPD.
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            Validity of Six Activity Monitors in Chronic Obstructive Pulmonary Disease: A Comparison with Indirect Calorimetry

            Reduced physical activity is an important feature of Chronic Obstructive Pulmonary Disease (COPD). Various activity monitors are available but their validity is poorly established. The aim was to evaluate the validity of six monitors in patients with COPD. We hypothesized triaxial monitors to be more valid compared to uniaxial monitors. Thirty-nine patients (age 68±7years, FEV1 54±18%predicted) performed a one-hour standardized activity protocol. Patients wore 6 monitors (Kenz Lifecorder (Kenz), Actiwatch, RT3, Actigraph GT3X (Actigraph), Dynaport MiniMod (MiniMod), and SenseWear Armband (SenseWear)) as well as a portable metabolic system (Oxycon Mobile). Validity was evaluated by correlation analysis between indirect calorimetry (VO2) and the monitor outputs: Metabolic Equivalent of Task [METs] (SenseWear, MiniMod), activity counts (Actiwatch), vector magnitude units (Actigraph, RT3) and arbitrary units (Kenz) over the whole protocol and slow versus fast walking. Minute-by-minute correlations were highest for the MiniMod (r = 0.82), Actigraph (r = 0.79), SenseWear (r = 0.73) and RT3 (r = 0.73). Over the whole protocol, the mean correlations were best for the SenseWear (r = 0.76), Kenz (r = 0.52), Actigraph (r = 0.49) and MiniMod (r = 0.45). The MiniMod (r = 0.94) and Actigraph (r = 0.88) performed better in detecting different walking speeds. The Dynaport MiniMod, Actigraph GT3X and SenseWear Armband (all triaxial monitors) are the most valid monitors during standardized physical activities. The Dynaport MiniMod and Actigraph GT3X discriminate best between different walking speeds.
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              The minimal important difference of exercise tests in severe COPD.

               Milo A. Puhan,  Robert Wise,   (2011)
              Our aim was to determine the minimal important difference (MID) for 6-min walk distance (6MWD) and maximal cycle exercise capacity (MCEC) in patients with severe chronic obstructive pulmonary disease (COPD). 1,218 patients enrolled in the National Emphysema Treatment Trial completed exercise tests before and after 4-6 weeks of pre-trial rehabilitation, and 6 months after randomisation to surgery or medical care. The St George's Respiratory Questionnaire (domain and total scores) and University of California San Diego Shortness of Breath Questionnaire (total score) served as anchors for anchor-based MID estimates. In order to calculate distribution-based estimates, we used the standard error of measurement, Cohen's effect size and the empirical rule effect size. Anchor-based estimates for the 6MWD were 18.9 m (95% CI 18.1-20.1 m), 24.2 m (95% CI 23.4-25.4 m), 24.6 m (95% CI 23.4-25.7 m) and 26.4 m (95% CI 25.4-27.4 m), which were similar to distribution-based MID estimates of 25.7, 26.8 and 30.6 m. For MCEC, anchor-based estimates for the MID were 2.2 W (95% CI 2.0-2.4 W), 3.2 W (95% CI 3.0-3.4 W), 3.2 W (95% CI 3.0-3.4 W) and 3.3 W (95% CI 3.0-3.5 W), while distribution-based estimates were 5.3 and 5.5 W. We suggest a MID of 26 ± 2 m for 6MWD and 4 ± 1 W for MCEC for patients with severe COPD.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                28 April 2016
                2016
                : 11
                : 4
                Affiliations
                [1 ]KU Leuven-University of Leuven, Department of Rehabilitation Sciences, B-3000 Leuven, Belgium
                [2 ]University Hospitals Leuven, Department of Respiratory Diseases, B-3000 Leuven, Belgium
                [3 ]Center for research in environmental epidemiology (CREAL), Barcelona, Spain
                [4 ]Rehabilitation Research Centre, Biomedical Research Institute, Faculty of Medicine and Life Sciences, Hasselt University, Diepenbeek, Belgium
                [5 ]University Hospitals Leuven, Department of Cardiovascular Sciences, B-3000 Leuven, Belgium
                [6 ]Red Cross Flanders, Centre for Evidence-Based Practice, Mechelen, Belgium
                Pondicherry Institute of Medical Sciences, INDIA
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: HD TT. Performed the experiments: HD CB MH HVR DL. Analyzed the data: HD TT. Contributed reagents/materials/analysis tools: TT WJ. Wrote the paper: HD TT. Critically reviewed the manuscript: CB MH HVR DL WJ CAC. Took responsibility for the content of the manuscript and provided the study idea: TT.

                Article
                PONE-D-15-40512
                10.1371/journal.pone.0154587
                4849755
                27124297
                © 2016 Demeyer et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Page count
                Figures: 2, Tables: 5, Pages: 11
                Product
                Funding
                Funded by: Flemisch Research Foundation
                Award ID: grant # G.0871.13
                Award Recipient :
                Funded by: PROactive IMI JU
                Award ID: # 115011
                Award Recipient :
                Funded by: FWO Flanders
                Award ID: post-doctoral research fellows
                Award Recipient :
                Funded by: FWO Flanders
                Award ID: post-doctoral research fellows
                Award Recipient :
                Funded by: CNPq/Brazil
                Award ID: 202425/2011-8
                Award Recipient :
                Funded by: joint ERS/SEPAR Fellowship (LTRF 2015)
                Award ID: post-doctoral research fellow
                Award Recipient :
                This work was supported by the Flemish Research Foundation (grant # G.0871.13) and PROactive IMI-JU # 115011. DL and WJ are post-doctoral research fellows of the FWO-Flanders. CAC is supported by CNPq/Brazil (202425/2011-8). Ms Heleen Demeyer is the recipient of a joint ERS/SEPAR Fellowship (LTRF 2015).
                Categories
                Research Article
                Medicine and Health Sciences
                Pulmonology
                Chronic Obstructive Pulmonary Disease
                Medicine and Health Sciences
                Public and Occupational Health
                Physical Activity
                Medicine and Health Sciences
                Health Care
                Health Care Facilities
                Hospitals
                Biology and Life Sciences
                Biomechanics
                Biological Locomotion
                Walking
                Biology and Life Sciences
                Physiology
                Biological Locomotion
                Walking
                Medicine and Health Sciences
                Physiology
                Biological Locomotion
                Walking
                Biology and Life Sciences
                Chronobiology
                Daylight
                Ecology and Environmental Sciences
                Daylight
                Research and Analysis Methods
                Research Assessment
                Research Validity
                Research and Analysis Methods
                Research Design
                Retrospective Studies
                Medicine and Health Sciences
                Rehabilitation Medicine
                Gait Rehabilitation
                Custom metadata
                All relevant data are within the paper and its Supporting Information files.

                Uncategorized

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