Chronic obstructive pulmonary disease (COPD) is a common, complex disorder associated with substantial morbidity and mortality. COPD is defined by irreversible airflow obstruction due to chronic bronchitis, emphysema, and/or small airways disease. Airflow obstruction is typically determined by reductions in quantitative spirometric indices, including forced expiratory volume at 1 second (FEV1) and the ratio of FEV1 to forced vital capacity (FVC) (Silverman et al., 2002; Celedon et al., 2004).