Abstract
BackgroundChronic obstructive pulmonary disease (COPD) is supposed to be classified on the basis of post-bronchodilator lung function. Most longitudinal studies of COPD, though, do not have post-bronchodilator lung function available. We used pre-and post bronchodilator lung function data from the Lung Health Study to determine whether these measures differ in their ability to predict mortality.MethodsWe limited our analysis to subjects who were of black or white race, on whom we had complete data, and who participated at either the 1 year or the 5 year follow-up visit. We classified subjects based on their baseline lung function, according to COPD Classification criteria using both pre- and post-bronchodilator lung function. We conducted a survival analysis and logistic regression predicting death and controlling for age, sex, race, treatment group, smoking status, and measures of lung function (either pre- or post-bronchodilator. We calculated hazard ratios (HR) with 95% confidence intervals (CI) and also calculated area under the curve for the logistic regression models.ResultsBy year 15 of the study, 721 of the original 5,887 study subjects had died. In the year 1 sample survival models, a higher FEV1 % predicted lower mortality in both the pre-bronchodilator (HR 0.87, 95% CI 0.81, 0.94 per 10% increase) and post-bronchodilator (HR 0.84, 95% CI 0.77, 0.90) models. The area under the curve for the respective models was 69.2% and 69.4%. Similarly, using categories, when compared to people with "normal" lung function, subjects with Stage 3 or 4 disease had similar mortality in both the pre- (HR 1.51, 95% CI 0.75, 3.03) and post-bronchodilator (HR 1.45, 95% CI 0.41, 5.15) models. In the year 5 sample, when a larger proportion of subjects had Stage 3 or 4 disease (6.4% in the pre-bronchodilator group), mortality was significantly increased in both the pre- (HR 2.68, 95% CI 1.51, 4.75) and post-bronchodilator (HR 2.46, 95% CI 1.63, 3.73) models.ConclusionsBoth pre- and post-bronchodilator lung function predicted mortality in this analysis with a similar degree of accuracy. Post-bronchodilator lung function may not be needed in population studies that predict long-term outcomes.
Highlights
Chronic obstructive pulmonary disease (COPD) is supposed to be classified on the basis of postbronchodilator lung function
Response to a bronchodilator is thought to be important in COPD diagnosis and guidelines suggest that classification of COPD be made using spirometry performed after bronchodilator administration [4]
The rationale for using these visits was that the inclusion criteria limited the range of lung disease severity at baseline to mild and moderate COPD, whereas a broader range could be seen in subsequent visits
Summary
Chronic obstructive pulmonary disease (COPD) is supposed to be classified on the basis of postbronchodilator lung function. We used pre-and post bronchodilator lung function data from the Lung Health Study to determine whether these measures differ in their ability to predict mortality. GOLD defines COPD as a preventable and treatable disease with airflow limitation that is usually progressive and associated with an abnormal inflammatory response of the lung to noxious particles or gases [4]. Both the American Thoracic Society (ATS) and the European Respiratory Society (ERS) have, in large part, adopted this definition [5]. In a random population study to determine spirometry reference values, post-bronchodilator values differed from pre-bronchodilator values [8]. Most longitudinal studies looking at the effect of impaired lung function on outcomes such as mortality and hospitalizations have used pre-bronchodilator lung function [11,12,13,14]
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