RATIONALE Recent evidence indicates that the rate of lung function decline is steepest in mild COPD and slower in moderate to severe COPD. The current study assessed whether lung function decline relates to baseline airflow obstruction severity in male heavy smokers. METHODS In total, 2,003 male smokers with a mean (SD) age of 59.8 (5.3) years underwent pulmonary function testing at baseline and after 3 year follow-up. Participants were classified by entry FEV(1)/FVC as follows: Group 1, >70 Group 2, <70% but >LLN; and group 3, <LLN. Differences in lung function decline among the groups were assessed using multiple regression after adjustment for packyears, smoking status (current/former smoker), presence/absence of mucus production, centre, height, age, CT-derived emphysema severity (Perc15), observation time (years in study) and the baseline values. RESULTS Over three years, the mean (SD) FEV(1)/FVC , FEV(1) and MEF(50) decreases in Group 1 were 3.1% (1), 0.21 L (0.07) and a 0.40 L/s (0.26), respectively. In Group 3, these decreases were 2.4% (1.1), 0.15 L (0.08) and 0.06 L/s (0.19), respectively. All lung function parameters showed the greatest decline in Group 1 (p<0.001). CONCLUSION Diagnosing COPD based on the presence of more severe airflow obstruction (as defined by FEV(1)/FVC <LLN) means that, at the time of such a diagnosis, subjects passed the phase of strong lung function decline.
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