Chronic Obstructive Pulmonary Disease (COPD) is the 4th leading cause of death in the U.S. Worldwide, COPD ranked sixth as the cause of death in 1990. It is 
projected to be the third leading cause of death worldwide by 2020 due to an increase in smoking rates and demographic changes in many countries, and the economic burden of COPD in the U.S. in 2007 was $42.6 billion in health care costs and lost productivity (wikipedia.org).
The etiology of COPD primarily caused by chronic tobacco smoking (pack in years), others caused by occupational exposures( dusts from workplaces), air pollution, genetics, and can be an autoimmune disease. According to a journal published in NEJM at March 2009, pulmonary rehabilitation does not directly improve lung mechanics or gas exchange.
Exercise training does ease other manifestations of COPD, increasing exercise tolerance, reducing dyspnea, and improving quality of life but not for lung improvement. A patient which has been candidated for pulmonary rehabilitation, it is recommended to perform a stress test for cardiovascular evaluation, perhaps in the form of a cardiopulmonary exercise test before begin a treatment, according to this journal.
You can find many sections such as clinical problem, pathophysiology and effect of therapy, and recommendations for COPD pulmonary rehabilitation in this journal. Complete read of Does Exercise Training Can Improve COPD’s Lung Functions? can be downloaded in 7 pages, 320 Kb of pdf format type (source: nejm.org). See another Pulmonary Journal in this site.
