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Reference equations of PA using associated factors for COPD patients. PA: physical activity; COPD: chronic obstructive pulmonary disease; mMRC: modified Medical Research Council dyspnea scale; IC: inspiratory capacity; 6MWD: 6-minute walk distance; HADS-A: anxiety score of the Hospital Anxiety and Depression Scale; FEV1%pred: forced expiratory volume in one second percent of predicted value; BNP: serum brain natriuretic peptide. Quoted from references [67,68].
