The FVC measurement indicates the amount of air a person can forcefully and quickly exhale after taking a deep breath.

Incidence of AEs and SAEs, incidence of abnormal clinical laboratory parameters, abnormal vital signs, and abnormal 12-lead ECGs

Assess the effect of continued therapy with oral treprostinil on exercise capacity as assessed by the change from Baseline in 6-Minute Walk Test (6MWT) after 1 year of treatment. The 6MWT is the clinical standard for assessing subject functional status in the treatment of PAH and has been considered an objective measure of subject functional status by the American Thoracic Society. The distance a subject can walk in 6 minutes is recorded in meters.

Change in peak 6-minute walk distance from baseline to Week 12. Peak 6MWD was defined as a 6-minute walk test (6MWT) within 10 to 60 minutes after study drug inhalation

Defined as the region with ventilation signals \< mean - 2SD, measured by HP129XeMRI and expressed as a percentage of total lung volume.

Defined as the region with membrane signals \< mean - 2SD, measured by HP129XeMRI and expressed as a percentage of total lung volume.

Defined as the region with membrane signals between 1SD and 2SD below the mean, measured by HP129XeMRI and expressed as a percentage of total lung volume.

Defined as the region with RBC transfer signals \< mean - 2SD, measured by HP129XeMRI and expressed as a percentage of total lung volume.

Defined as the region with RBC transfer signals between 1SD and 2SD below the mean, measured by HP129XeMRI and expressed as a percentage of total lung volume.

Measured using HP129XeMRI spectroscopy as a surrogate for pulmonary vascular resistance, normalized to RBC transfer signal intensity.

Frequency shift in RBC signal reflecting capillary blood oxygenation, measured using HP129XeMRI spectroscopy.

Change in RHC parameter PVR (pulmonary vascular resistance )

Change in RHC parameter mPAP (mean pulmonary arterial pressure)

Number of participants with treatment-related adverse events following treatment with oral treprostinil at 12 months. We defined adverse event as any untoward medical experience occurring to a subject during a clinical trial whether or not it is related to the study drug.

Median rate of change of calcinosis in radiograph following treatment with oral treprostinil as assessed by the Scleroderma Clinical Trial Consortium (SCTC) radiographic scoring system. Historical average SCTC scores in this patient population have ranged from 4.08 to 472.88, with higher scores indicating more severe symptoms. The SCTC radiographic score for calcinosis is a validated radiographic scoring system to assess the severity of calcinosis affecting the hands of patients with SSc that accounts for area coverage, density, and anatomic location, higher scores mean worse calcinosis. Physician rates density and percentage of area for 22 regions of each hand, each deferentially weighted in the overall score; individual region values are multiplied my their weight then summed to create an overall score.

American Thoracic Society (ATS) Practice Guideline based 6-minute walk (6MW) distance

The intent of the 6MWD test is to evaluate exercise capacity associated with carrying out activities of daily living. Change in 6MWD from Baseline to Week 16, correlates with the current clinical standard for assessing patient functional status in the treatment of PH and is considered an objective measure of patient functional status. Subjects will be instructed to walk down a corridor at a comfortable speed as far as they can manage for six minutes. Peak exposure 6MWD will occur by conducting 6-minute walk test (6MWT) within 10 to 60 minutes after the most recent dose of study drug dose.

A successful transition was defined as a subject from Cohort 1 or Cohort 2 who was receiving oral treprostinil and no longer receiving IV/SC Remodulin or inhaled prostacyclin, respectively, at Week 4 and clinically maintained on oral treprostinil treatment through Week 24. A successful initiation of oral treprostinil for Cohort 3 was defined as a subject who was clinically maintained on oral treprostinil through Week 24.

6MWD was evaluated at study entry and after 3 weeks of treatment with TreT.

Subject satisfaction with and preference for the inhaled treprostinil device was evaluated with the Preference Questionnaire for Inhaled Treprostinil Devices (PQ-ITD). The PQ-ITD is a questionnaire given to evaluate subject satisfaction with and preference for inhaled treprostinil devices. The questionnaire provides 12 different statements around inhaled device satisfaction and allows for 5 response options: strongly disagree, disagree, neutral, agree, and strongly agree.

Patient-reported PAH symptoms and impact were evaluated with the PAH Symptoms and Impact (PAH-SYMPACT) Questionnaire. The PAH-SYMPACT is a 23-item patient-reported outcome questionnaire that consists of 11 symptom items, 11 impact items, and 1 item on oxygen use. The symptom items are divided into cardiopulmonary and cardiovascular domains, and the impact items are divided into physical and emotional/cognitive domains. Symptom and impact domain scores (range 0 to 4) are calculated as the sum of the scores for the items included in the domain divided by the number of items in the domain. For all domains, a higher score indicates more severe symptoms/impacts.

Patient-reported PAH symptoms and impact were evaluated with the PAH Symptoms and Impact (PAH-SYMPACT) Questionnaire. The PAH-SYMPACT is a 23-item patient-reported outcome questionnaire that consists of 11 symptom items, 11 impact items, and 1 item on oxygen use. The symptom items are divided into cardiopulmonary and cardiovascular domains, and the impact items are divided into physical and emotional/cognitive domains. Symptom and impact domain scores (range 0 to 4) are calculated as the sum of the scores for the items included in the domain divided by the number of items in the domain. For all domains, a higher score indicates more severe symptoms/impacts.

Stroke volume augmentation is a physiologic parameter which reflects the hearts ability to respond to physiologic demands of exercise. Stroke volume can be inferred during cardiopulmonary exercise testing by calculating the O2 pulse. Oxygen uptake (VO2) and heart rate are directly measured during cardiopulmonary exercise testing. O2 pulse is calculated by dividing VO2 by heart rate. Stroke volume augmentation is the ratio of O2 pulse at baseline (at the beginning of exercise) and at anaerobic threshold. Stroke volume augmentation will be measured before and after treatment with inhaled treprostinil to assess for improvements in heart function during exercise.