Relationship between exacerbation frequency and lung function decline in chronic obstructive pulmonary disease.

Background: Chronic obstructive pulmonary disease (COPD) is characterised by both an accelerated decline in lung function and periods of acute deterioration in symptoms termed exacerbations. The aim of this study was to investigate whether these are related.

Methods: Over 4 years, peak expiratory flow (PEF) and symptoms were measured at home daily by 109 patients with COPD (81 men; median (IQR) age 68.1 (63-74) years; arterial oxygen tension (PaO(2)) 9.00 (8.3-9.5) kPa, forced expiratory volume in 1 second (FEV(1)) 1.00 (0.7-1.3) l, forced vital capacity (FVC) 2.51 (1.9-3.0) l); of these, 32 (29 men) recorded daily FEV(1). Exacerbations were identified from symptoms and the effect of frequent or infrequent exacerbations (> or < 2.92 per year) on lung function decline was examined using cross sectional, random effects models.

Results: The 109 patients experienced 757 exacerbations. Patients with frequent exacerbations had a significantly faster decline in FEV(1) and peak expiratory flow (PEF) of -40.1 ml/year (n=16) and -2.9 l/min/year (n=46) than infrequent exacerbators in whom FEV(1) changed by -32.1 ml/year (n=16) and PEF by -0.7 l/min/year (n=63). Frequent exacerbators also had a greater decline in FEV(1) if allowance was made for smoking status. Patients with frequent exacerbations were more often admitted to hospital with longer length of stay. Frequent exacerbations were a consistent feature within a patient, with their number positively correlated (between years 1 and 2, 2 and 3, 3 and 4).

Conclusions: These results suggest that the frequency of exacerbations contributes to long term decline in lung function of patients with moderate to severe COPD.