Patients satisfying the eligibility criteria, have at least 32 consecutive days of inhalation times data during period one (baseline), and have at least 6 consecutive days of inhalation time data after beginning period two (active), will be included in the analysis for evaluating improvements in inhalation times associated with use of PD-15. Patients who have a change (dosing change,new medication or elimination of a medication) in their PAH medications during period two, will have their data truncated at the time of the first change in medication. Patients who do not follow the prescribing and patient information labeling for Ventavis during period two will be excluded.

Inclusion Criteria:

• Male or female, aged 18-85 years
• Have a current diagnosis of symptomatic PAH classified by one of the following: a) IPAH or FPAH; b) PAH associated with one of the following connective tissue diseases and mild or no lung parenchymal disease: scleroderma spectrum of disease, systemic lupus erythematosis, or mixed connective tissue disease, c) PAH associated with repaired atrial septal defect (ASD), ventricular septal defect (VSD), or patent ductus arteriosus (PDA) ≥ 1 year post-operative from Screening, d) PAH associated with HIV, or e) PAH associated with the use of anorexigens (e.g. fenfluramine- phentermine)
• On a stable and well tolerated dose regimen of Ventavis (5 μg per dose) for at least 4 weeks prior to the Screening visit, using the I-neb AAD System equipped with power disc 6

Exclusion Criteria:

• Receipt of any prostacyclin or prostacyclin analogue other than Ventavis within the 12 weeks preceding the Screening visit
• Receipt of atrial septostomy within the 6 months preceding Screening
• History of left-sided heart disease
• Clinically relevant obstructive lung disease
• Chronic renal or liver disease
• Uncontrolled systemic hypertension or hypotension
• Cerebrovascular event within the 6 months preceding Screening