3921680 ECOPD exacerbations of chronic obstructive pulmonary disease 57 3921681 ECOPD exacerbations of COPD 48 3921687 ECOPD Early Chronic Obstructive Pulmonary Disease 7 3921688 ECOPD Early COPD 2 3921686 ECOPD episodes of exacerbation 2 3921689 ECOPD experiencing COPD exacerbations 2