Reference Equations for Assessing the Physical Activity of Japanese Patients with Chronic Obstructive Pulmonary Disease

BACKGROUND: To improve physical activity (PA) in patients with chronic obstructive pulmonary disease (COPD), providing a target PA value based on the individual patient’s condition may be a useful interventional strategy. However, to determine the target value, a predictive PA value for each patient is required. RESEARCH QUESTION: What is the reference equation consisting of PA-related factors to determine the predictive PA value for each patient with COPD? MATERIAL AND METHODS: In this prospective cross-sectional observational study, we measured the PA with a triaxial accelerometer and several other factors including demographic factors, pulmonary function, dyspnea, exercise capacity, muscle strength, nutrition, and indicators of several comorbidities in stable Japanese outpatients with COPD aged ≥40 years old and detected PA-related factors by a multiple regression analysis and stepwise method. We created reference equations for four indices of PA using multiple linear regression equations. RESULTS: Two hundred and twenty-seven patients were registered. The equations of duration at ≥2.0 metabolic equivalents (METs) and step count consisted of 4 factors: 6-minute walk distance, modified Medical Research Council dyspnea scale, anxiety score of the Hospital Anxiety and Depression Scale, and the forced expiratory volume in 1 second % of predicted value. Those of duration at ≥3.0 METs and total activity at ≥3.0 METs consisted of 5 factors: the above 4 factors and age or brain natriuretic peptide. There was no fixed bias or proportional bias between the measured and predictive values in patients with non-high measured PA values. CONCLUSION: We determined reference equations for four indicators of PA using PA-related factors in Japanese patients with COPD. The predictive values calculated using the equations could be useful for deciding target PA values for each patient. CLINICAL TRIAL REGISTRATION: UMIN-CTR; No.: UMIN000025459; URL: https://www.umin.ac.jp/ctr/index.htm.