Smokers are assessed for COPD using spirometry, with COPD defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) as airflow limitation not fully reversible with bronchodilators. There is a subset of smokers with normal spirometry (by GOLD criteria), who have a low diffusion capacity (DLCO), a parameter linked to emphysema and small airway disease. The natural history of these “normal spirometry/low DLCO” smokers is unknown.
From a cohort of 1570 smokers in the New York City metropolitian area, all of whom had normal spirometry, two groups were randomly selected for lung function follow-up: smokers with normal spirometry/normal DLCO (n=59) and smokers with normal spirometry/low DLCO (n=46). All had normal history, physical examination, CBC, urinalysis, HIV status, α1-antitrypsin level, chest X-ray, FEV1, FVC, FEV1/FVC ratio and total lung capacity (TLC). Throughout the study, all continued to be active smokers.