Subject recruitment
Patients who had been admitted to the Prince of Wales Hospital with AECOPD were recruited for this study. Subjects with pneumonic changes on the chest radiographs were excluded. Age and sex-matched COPD subjects at stable state (without AECOPD for at least 10 weeks) and healthy, non-smoking subjects were recruited as controls.
Collection of exhaled breath condensate (EBC) EBC was collected using the EcoScreen (VIASYS Healthcare, Conshohochen, PA, USA) according to the manufacturer's instructions. EBC was stored in 250 microL aliquots immediately at -70oC until analysis. EBC was collected on Day 5, 14, 30 and 60 after hospitalization for subjects with AECOPD. For the stable COPD patients and normal controls, EBC collection was performed once.
Measurement of TNF alpha, LTB4 and IL-8 The concentrations of TNF alpha, LTB4, and IL-8 in EBC were measured in one batch by high-sensitivity sandwich enzyme immunoassays (TNF alpha and IL-8 from BioSource International, Camarillo, CA, USA; LTB4 from Cayman Chemical Company, Ann Arbor, MI, USA) according to the manufacturers' instructions. Intra-subject repeatability of TNF alpha, LTB4 and IL-8 was assessed by collection of EBC in stable COPD subjects. EBC was collected as described above at the same time (09:00 to 10:00) on 2 consecutive days.
