Transition From Injectable Prostacyclin Medication to Inhaled Prostacyclin Medication

The purpose of this study is to assess tolerability and clinical effects of transition from intravenous (IV, needle in the vein) or subcutaneous (SQ, needle in the skin) to the recently-approved inhaled treprostinil (Tyvaso) for the treatment of pulmonary arterial hypertension (PAH). Our hypothesis is that the transition to inhaled treprostinil will be tolerated by patients. The intravenous and subcutaneous drugs epoprostenol and treprostinil received approval for treatment of PAH many years ago. While these medications improve exercise capacity and the symptoms of PAH, they are given by injection and thus have several side effects, such as pain and catheter infection. This has resulted in many patients either refusing to take the medication or quitting these medications because of not tolerating them. The only other form of prostacyclin treatment available for PAH patients is inhaled. There are 2 inhaled prostacyclins approved for PAH, however one of these requires at least 6 inhalations per day, every day, and takes about 30 minutes to inhale each time. Thus, it has not been a regularly-used medication and issues surrounding compliance make it a riskier drug to use if patients do not get their full doses every day. The other inhaled medication, treprostinil, was approved a few months ago, only needs to be given 4 times a day, and takes about 2-3 minutes to inhale. Since inhaled treprostinil can be administered easily, it is anticipated that many patients will transition from epoprostenol or treprostinil to the recently approved inhaled treprostinil, however we do not know if this is a safe or effective way to manage patients. Thus, the goal of this prospective study is to gather observational data regarding how that switch is made, tolerability of the switch, and, to the extent possible with this methodology, assess clinical effects of the switch. This is a prospective study. Twenty patients \> 18 years old with PAH will be enrolled. Patients enrolled will be