PECAM1 and chronic obstructive pulmonary disease: CD144+ EMVs ↑ & CD31+ EMVs ↑ & CD62E+ EMVs ↑ (stable patients vs healthy controls; patients with exacerbated COPD vs stable COPD patients);CD62E+ EMVs ↑ (patients with frequent exacerbations vs those with no frequent exacerbations)