Clinical Study of Pulsed, Inhaled Nitric Oxide Versus Placebo in Symptomatic Subjects With PAH

Inclusion Criteria: 1. Signed Informed Consent Form (and assent as appropriate) prior to the initiation of any study mandated procedures or assessments 2. A confirmed diagnosis of PAH Group 1 who have either idiopathic PAH (IPAH), heritable PAH, drug and toxin-induced PAH, associated PAH (APAH) with connective tissue disease (CTD), APAH with repaired simple congenital systemic to pulmonary shunt (i.e., atrial septal defect, ventricular septal defect and/or patent ductus arteriosus; complete repair at least 1 year prior to Screening), APAH with human immunodeficiency virus (HIV), or APAH with portal hypertension 3. Subjects receiving at least one PAH specific therapy (ERA or PDE-5 inhibitor, or inhaled, subcutaneous, or intravenous prostacyclin or a prostacyclin analog) with the same type of therapy for at least 3 months with stable dosing 4 weeks prior to Screening. (Subjects should be receiving optimal therapy according to the disease severity) 4. Subjects using oxygen therapy by nasal cannula for at least 4 weeks prior to Screening 5. PAH diagnosis confirmed by RHC within the previous 5 years, according to the following definitions: * PVR ≥ 400 dynes.sec.cm-5 (5 Wood units) * mPAP ≥ 25 mmHg * PCWP or LVEDP ≤ 15 mmHg * Subjects who otherwise meet all the inclusion criteria and none of the exclusion criteria but have not undergone a RHC within the previous 5 years may be considered eligible for the study if they undergo a RHC and then meet the pulmonary hemodynamics criterion 6. 6MWD ≥ 100 meters and ≤ 450 meters prior to randomization 7. WHO Functional Class II-IV. Subjects with WHO Functional Class IV should be treated with prostacyclin or a prostacyclin analog (subcutaneous or intravenous), plus at least one additional PAH specific therapy (ERA or PDE-5), if available to the subject and reimbursed by health insurance 8. Age between 18 and 85 years (inclusive) 9. Willingness to use INOpulse delivery device for at least 12 hours per day 10. Willingness to continue on study drug until the subject has completed Week 18 assessments 11. Female subjects of childbearing potential must have a negative pre-treatment pregnancy test (serum or urine). All female subjects should take adequate precaution to avoid pregnancy. Exclusion Criteria: 1\. Subjects with known HIV infection who have a history within the past 3 months of any opportunistic pulmonary disease (e.g., tuberculosis, Pneumocystis carinii pneumonia, or other pneumonias) at the time of Screening 2. PAH associated with untreated thyroid disorders, glycogen storage disease, Gaucher's disease, hereditary hemorrhagic telangiectasia, hemoglobinopathies, myeloproliferative disorders or splenectomy 3. Subjects with pulmonary conditions that may contribute to PAH including, but not limited to, chronic bronchiectasis, cystic fibrosis, or other pulmonary condition that the Investigator may deem to contribute to the severity of the disease or impair the delivery of iNO due to airway disease 4. Subjects receiving riociguat 5. Subjects receiving oral prostanoids as monotherapy 7. PAH associated with significant venous or capillary involvement, known or suspected pulmonary veno-occlusive disease, or pulmonary capillary hemangiomatosis 8. Any subject with WHO PH Groups 2, 3, 4 or 5 9. Subjects with any of the following cardiac abnormalities: a. Underlying cardiomyopathy or clinically significant aortic or mitral valve disease in the opinion of the investigator b. Left ventricular systolic dysfunction (LVSD), i.e., left ventricular ejection fraction (LVEF) \< 40% or left ventricular shortening fraction (LVSF) \< 22%, as determined by local reading c. Current symptomatic coronary artery disease, myocardial infarction within 1 year, or any coronary artery interventions within 6 months 10. Systemic hypertension defined as systolic blood pressure (SBP) \> 160 mmHg and/or diastolic blood pressure (DBP) \> 100 mmHg persistent at Screening after a period of rest (treated or untreated) 11. Subjects with a history of deep vein thrombosis, pulmonary embolism/infarction or prothrombotic disorder must have had chronic thromboembolic pulmonary hypertension (CTEPH) excluded by ventilation/perfusion lung (V/Q) scan 12. Severe obstructive lung disease defined as both a forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) \< 70% and FEV1 \< 55% of predicted value 13. Moderate to severe restrictive lung disease: total lung capacity (TLC) \< 60% of predicted; if TLC 60% to 70% predicted, a high resolution CT scan showing diffuse disease or more than mild patchy disease 14. Any subject who develops or has developed a PCWP \> 20 mmHg during acute vasodilator testing (AVT) 15. Systemic hypotension defined as SBP \< 90 mmHg persistent at Screening after a period of rest 16. Moderate to severe hepatic impairment, i.e., Child-Pugh Class B or C 17. On dialysis 18. Acute or chronic physical impairment (other than dyspnea due to PAH) that would limit the ability to comply with study procedures or adherence to therapy (i.e., 6MWT), including carrying and wearing the pulsed delivery device per study protocol, or medical problem(s) likely to preclude completion of the study 19. Pregnant or breastfeeding females at Screening 20. Administered L-arginine within 1 month prior to Screening 21. Known concomitant life-threatening disease with a life expectancy less than 1 year 22. Atrial septostomy within 3 months preceding randomization 23. The concurrent use of the INOpulse device with a continuous positive airway pressure (CPAP), Bilevel positive airway presure BiPAP, or any other positive pressure device. 24\. Use of investigational drugs or devices within 1 month prior to Screening (other than acute vasodilator testing with iNO) 25. Any underlying medical or psychiatric condition that, in the opinion of the Investigator, makes the subject an unsuitable candidate for the study 26. Any subject who has been enrolled in any previous clinical study with inhaled NO administered through pulse delivery.