Abstract
Long-term decline in lung function is generally considered to be progressive in individuals with established chronic obstructive pulmonary disease (COPD), despite the presence of intersubject variation. We hypothesized that the annualized rate of decline in forced expiratory volume in 1 second (FEV(1)) would not be constant among different time periods in the natural history of established COPD. We compared the annual change rates in FEV(1) during the first 5 years and the last 5 years, estimated separately using a linear mixed-effects model in 10-year survivors (n = 110). The subjects were classified into three FEV(1) decline groups, based on the 25th and 75th percentile values in each time period. The rates of FEV(1) changes, calculated from the first 5 years and the last 5 years, did not correlate with each other among 10-year survivors; the subjects of each FEV(1) decline group during the first 5 years did not consistently remain in the same FEV(1) decline group during the last 5 years. Smoking status and exacerbation frequency were not associated with decline in FEV(1). In conclusion, the disease activity, which is often expressed as annualized change in FEV(1), might be changeable either way over years in patients with established COPD.