This study is for adults with pulmonary arterial hypertension (PAH), a condition where blood pressure in the lungs is higher than normal. The study looks at how safe and tolerable a medicine called LIQ861 (treprostinil) inhalation powder is, when people switch from an oral medicine, selexipag, to this new inhaled form. Everyone in the study will use a small handheld device to inhale LIQ861 four times a day for 16 weeks. The dose might go up if it is well tolerated. Researchers will also check if this switch impacts how far participants can walk, a blood marker for heart strain, and symptoms reported by participants.

Key Points:

• Participants will use LIQ861 for 16 weeks and may need to visit the study site for monitoring.
• The study is open to adults aged 18-80 with specific types of PAH.
• Participants must be able to use the dry powder inhaler correctly.