Inter-relationships among neutrophilic inflammation, air trapping and future exacerbation in COPD: an analysis of ECOPD study

BackgroundThe inter-relationships among neutrophilic airway inflammation, air trapping and future exacerbation in chronic obstructive pulmonary disease (COPD) remain unclear.ObjectiveTo evaluate the associations between sputum neutrophil proportions and future exacerbation in COPD and to determine whether these associations are modified by significant air trapping.MethodsParticipants with completed data were included and followed up to the first year in the Early Chronic Obstructive Pulmonary Disease study (n=582). Sputum neutrophil proportions and high-resolution CT-related markers were measured at baseline. Sputum neutrophil proportions were dichotomised based on their median (86.2%) to low and high levels. In addition, subjects were divided into the air trapping or non-air trapping group. Outcomes of interest included COPD exacerbation (separately any, severe and frequent exacerbation, occurring in the first year of follow-up). Multivariable logistic regressions were performed to examine the risk of severe exacerbation and frequent exacerbation with either neutrophilic airway inflammation groups or air trapping groups.ResultsThere was no significant difference between high and low levels of sputum neutrophil proportions in the exacerbation in the preceding year. After the first year of follow-up, subjects with high sputum neutrophil proportions had increased risks of severe exacerbation (OR=1.68, 95% CI: 1.09 to 2.62, p=0.020). Subjects with high sputum neutrophil proportions and significant air trapping had increased odds of having frequent exacerbation (OR=3.29, 95% CI: 1.30 to 9.37, p=0.017) and having severe exacerbation (OR=2.72, 95% CI: 1.42 to 5.43, p=0.003) when compared with those who had low sputum neutrophil proportions and non-air trapping.ConclusionsWe found that subjects with high sputum neutrophil proportions and significant air trapping are prone to future exacerbation of COPD. It may be a helpful predictor of future exacerbation.