SUN-101 or placebo will be administered twice daily as an oral inhalation using the investigational eFlow CS nebulizer. Approximately 150 subjects will be enrolled in the substudy (at selected sites only). These subjects will be required to participate in serial spirometry, vital signs, ECGs, and an additional Holter monitor assessment at Visit 6 (Week 12). This subset of subjects will be referred to as the Substudy Population.