RT Book, Section A1 Kasper, Dennis L. A1 Fauci, Anthony S. A1 Hauser, Stephen L. A1 Longo, Dan L. A1 Jameson, J. Larry A1 Loscalzo, Joseph SR Print(0) ID 1128786404 T1 Chronic Obstructive Pulmonary Disease T2 Harrison's Manual of Medicine, 19e YR 2016 FD 2016 PB McGraw-Hill Education PP New York, NY SN 9780071828529 LK accessmedicine.mhmedical.com/content.aspx?aid=1128786404 RD 2024/03/29 AB Chronic obstructive pulmonary disease (COPD) is a disease state characterized by chronic airflow obstruction; thus, pulmonary function testing is central to its diagnosis. The presence of airflow obstruction is determined by a reduced ratio of the forced expiratory volume in 1 s (FEV1) to the forced vital capacity (FVC). Among individuals with a reduced FEV1/FVC ratio, the severity of airflow obstruction is determined by the level of reduction in FEV1 (Table 131-1): ≥80% is stage I, 50–80% is stage II, 30–50% is stage III, and <30% is stage IV. Cigarette smoking is the major environmental risk factor for COPD. The risk of COPD increases with cigarette smoking intensity, which is typically quantified as pack-years. (One pack of cigarettes smoked per day for 1 year equals 1 pack-year.) Individuals with airway hyperresponsiveness and certain occupational exposures (e.g., coal mining, gold mining, and cotton textiles) are likely also at increased risk for COPD. In countries in which biomass combustion with poor ventilation is used for cooking, an increased risk of COPD among women has been reported. COPD is a progressive disorder; however, the rate of loss of lung function often slows markedly if smoking cessation occurs. In normal individuals, FEV1 reaches a lifetime peak at around age 25 years, enters a plateau phase, and subsequently declines gradually and progressively. Subjects can develop COPD by having reduced maximally attained lung function, shortened plateau phase, or accelerated decline in lung function.