 Chronic obstructive pulmonary disease COPD, the 3rd leading cause of death in the US, is a progressive disorder for which new treatments are urgently needed, as existing therapies are focused primarily on symptom relief. Oxidative stress, in part arising from inducible nitric oxide synthase iNOS released by the pulmonary vasculature, is critical for the development and progression of COPD; a treatment strategy focused on the pulmonary vasculature is hypothesized to be beneficial in COPD patients. This will be studied with the use of an inhaled prostacyclin analogue, iloprost, which has been approved for pulmonary hypertension and investigated in small studies of COPD patients. Potential mechanisms include reductions in dynamic hyperinflation during exercise in COPD patients or improvements in oxidative stress 