Simple standard equation for daily step count in Japanese patients with chronic obstructive pulmonary disease

Abstract

Purpose

The improvement of physical activity in patients with COPD is an important issue. However, no standard for the recommended number of steps for patients with COPD has been determined. We conducted a retrospective observational study to create a simple standard equation for the daily step count, which makes it easier to determine whether each subject is attaining his/her predicted value or not.

Patients and methods

Stable outpatients diagnosed with COPD whose physical activities had been measured using a triaxial accelerometer for more than 2 weeks were recruited from 5 institutes in Japan. Factors associated with the step count were detected by multivariate regression analysis. After the data were transformed to a normalized distribution, a multivariate linear regression equation was created using stepwise regression.

Results

One hundred sixty-two patients aged 72.3 (7.2) years and of FEV1 %pred 59.2 (22.8) % were recruited. Among the parameters, age, mMRC dyspnea scale and inspiratory capacity (IC) were detected by the stepwise method. The created standard equation was “Step count = (−0.079×[age]−1.595×[mMRC]+2.078×[IC]+18.149)³”. The correlations between the calculated values and the measured values were observed, and fixed, and proportional biases between them were also observed. When patients with <6500 steps/day were selected, no systematic bias between them could be detected.

Conclusion

A simple standard equation for Japanese patients with COPD was created using age, mMRC and IC, and could provide an individual-predicted value, especially for patients with <6500 steps/day.

Keywords:

• COPD
• physical activity
• behavior modification
• goal setting
• accelerometer

Supplementary materials

Subjects and methods

Stable outpatients with COPD were recreated at NHO Wakayama Hospital. COPD was diagnosed as a post-bronchodilator FEV1/FVC <0.7. AM and HJA-750C were worn on the waist of patients at the same time for 1 week. The step counts measured by both devices were compared. Written informed consent was obtained from all patients. This study has been approved by the ethics committee of NHO Wakayama Hospital (approved number 8, March 20, 2017) and has been registered with the University Hospital Medical Information Network (UMIN000016363, January 28, 2015).

Table S1 Characteristics of patients

Figure S1 Correlation between step counts by AM and HJA-750C. (A) scatter plot, r=0.990 P<0.0001 and (B) Bland–Altman plot. There was no systematic bias. (mean of difference 95% CI: −30.23 to 131.43, limit of agreement: −417.6 to 518.9). Broken lines indicate mean difference 95% CI and dotted lines indicate limit of agreement.

Abbreviations: HJA-750C, Active Style Pro HJA-750C; AM, Actimarker.

Acknowledgments

The authors thank Mr Brent Bell for proof reading the manuscript. This study was commissioned and supported by the Environmental Restoration and Conservation Agency of Japan.

Ethics approval and informed consent

This study has been approved by the ethics committee of Wakayama Medical University (approval number 2131, October 4, 2017) and also the ethics committee of each cooperative facility and has been registered with the University Hospital Medical Information Network (UMIN000029518, October 12, 2017). Written informed consent had been obtained from each patient at each institute. The contents of this study and the opportunity to reject the agreement were explained on the website of Third Department of Internal Medicine, Wakayama Medical University.

Data sharing statement

The clinical study data used to support the findings of this study are available from the corresponding author upon request.

Abbreviations

NHO, National Hospital Organization; AM, Actimarker; HJA-350, active style pro HJA-350; HJA-750C, active style pro HJA-750C; PA, physical activity; BMI, body mass index; IC, inspiratory capacity

Author contributions

All authors contributed to data analysis, drafting and revising the article, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

YM received lecturer fee from Nippon Boehringer Ingelheim. The authors report no other conflicts of interest in this work.