Primary Outcome Measures:
- Measuring circulating biomarkers of imatinib affect [ Time Frame: within one year of the end of the study ]
Secondary Outcome Measures:
- Evaluate effect of imatinib on the activation of mast cells [ Time Frame: within one year of the end of the study ]
We hypothesize that bone marrow progenitor cells are mobilized into the circulation in PAH, home to the lungs and differentiate into mast cells, which promote vascular remodeling and vasoconstriction through release of renin and chymase. As a corollary to this, we hypothesize that anti cKit tyrosine kinase inhibitor (TKI), imatinib, provides clinical benefit to patients through inhibition of mast cell progenitor proliferation, mobilization and differentiation. To test this, we will determine if mast cell progenitors and mast cell biomarkers are related to imatinib clinical response. This will be an ancillary study, part of a placebo-controlled, double-blind multi center clinical trial of imatinib in pulmonary arterial hypertension.