 - All subjects will be clinically stable for 4 weeks prior to inclusion. Clinical stability is defined as having no recent COPD exacerbations within the last 4 weeks and having received no antibiotics or change in their inhaled steroid dose during that time period. If a subject is on oral steroids, they will be required to be on 10 mg or less each day or no more than 20mg every other day to be eligible. If the oral steroid dose has been titrated over the previous 4 weeks either up or down or if the dose is higher than what has been described previously, they will be ineligible for the study. 