Visit 1 (Screening Visit): During the first visit, participants will have a brief exam by a pulmonary physician. The exam will include a complete blood count (CBC) to rule out anemia, baseline spirometry to assess lung volumes and flow rates to meet entry criteria, and in women of childbearing potential a pregnancy test. They will also be taken off theophylline and inhaled anticholinergics, but allowed to continue long acting inhaled beta agonists (LABA) or short acting beta agonist (SABA) for a rescue medication. Subjects on long acting inhaled beta agonists will be asked to discontinue this medication temporarily, 48 hr. prior to each study visit, but restarted upon completion of the visit.