ABSTRACT
Chronic obstructive pulmonary disease (COPD) is a syndrome characterized by abnormal tests of expiratory airflow (FEV1 and FEV1/FVC) that do not change markedly over several months of observations (1). Different levels of fixed airflow obstruction have been utilized to define COPD. No universally accepted thresholds for these continuous pulmonary function variables exist in the clinical literature. Some studies incorporate a decrease in the FEV1/FVC ratio into the definition, while other studies rely only on reduction in FEV1. It is important to recognize that the physiological definition of disease occurrence can be contrasted with the clinical criteria for the definition of chronic bronchitis, which traditionally utilizes cough and phlegm production for 3 months per year for 2 consecutive years (2). Pathological correlates of these physiological and epidemiological definitions are the presence of emphysema (defined as abnormal enlargement and destruction of airspaces beyond the terminal bronchiole) and inflammation at the level of the respiratory bronchiole (1). These disease-defining characteristics are not perfectly correlated. Airflow obstruction is more
likely with greater severity of anatomical emphysema, but a substantial fraction of subjects with airflow obstruction do not have significant emphysema, and some subjects with significant emphysema do not have airflow obstruction (3,4). To date, it remains unclear what genetic, environmental, and pathobiological factors contribute to this less than perfect correlation.
