The purpose of this study is to show that one form of mechanical airway clearance techniques, High Frequency Chest Wall Oscillation (HFCWO)using a pneumatic vest, will diminish exacerbations of COPD which will improve respiratory health status.

Approximately 60 to 70% of people with COPD have chronic cough and phlegm, the cardinal symptoms of chronic bronchitis or chronic mucus hypersecretion (CMH). Once thought to be a relatively benign condition, recent evidence shows that CMH in patients with established COPD is associated with greater decline in lung function, more frequent respiratory infections, more frequent exacerbations and increased mortality.Using mechanical airway clearance techniques (The Vest) will diminish exacerbations of COPD which will improve respiratory health status.

Comparison: Patients randomly assigned to the vest will have fewer exacerbations of COPD,better quality of life and less health care use compared to patients assigned to a sham vest.

Inclusion Criteria:

• Physician Diagnosis of COPD,chronic bronchitis and/or emphysema
• Forced Expiratory Volume in 1 second (FEV1)/ Forced Vital Capacity (FVC) < or = 70%
• FEV1 < or = 65%
• Current or former smoker > or = 20 pack years
• History of 1 or more COPD exacerbations in past 6 months necessitation hospitalization, Emergency Department (ED) visit, antibiotic or steroid prescription

Exclusion Criteria:

• Other lung diseases
• Co-morbid illnesses such as cancer, liver disease, cardiomyopathy
• Recent chest wall or abdominal trauma or surgery that would preclude using the vest

12 weeks