Chronic Obstructive Pulmonary Disease(COPD) is currently the fourth leading cause of death in the United States. COPD is characterized by reduced airflow that is largely irreversible and progressive. Smoking is recognized as the most important cause of COPD contributing up to 80% of the cases. The disease does demonstrate a significant variability in airflow obstruction during the progression of the disease among those who are diagnosed and treated. This is probably due not only to the role of exposure of cigarette smoke and other noxious inhaled particles and gases but also to the individual's varied responses to those exposures.