The care of patients with pulmonary arterial hypertension (PAH) has been greatly advanced over the recent years with high dose calcium channel blockers, epoprostanol, trepostinil, and bosentan.1 Much of this work has concentrated on the vascular endothelial and smooth muscle response to the various mediators of pulmonary vasodilation and constriction. Recent work has also implicated the erythrocyte (RBC) as an active participant in pulmonary vasodilation.2,3 Based on this work, we would like to present a case report of a patient with pulmonary arterial hypertension who received extensive RBC transfusions and experienced near complete remission of her pulmonary arterial hypertension.
A 39 y/o lady with a remote history of lupus and hemolytic anemia diagnosed at age 8 was treated with steroids and splenectomy. Since age 16, she had been in remission and off all rheumatalogic drugs. The patient was asymptomatic, had no evidence of cardiovascular disease, had 3 normal pregnancies, and had no history of smoking, drug or alcohol abuse. Two years ago, she developed new symptoms consistent with PAH. Right heart catheterization documented pulmonary arterial hypertension with pulmonary artery pressure 87/31 (mean 55), mean right atrial pressure 5, and cardiac index of 3.2 (by thermodilution, 2.45 by Fick). Exercise tolerance worsened to New York Heart Association Class (NYHA) IIIb, despite only mild obstruction on pulmonary function and unremarkable radiographic studies. Physical examination was remarkable for accentuated P2 and 1+ jugular venous distension. Continuous intravenous epoprostanol therapy (Flolan) was initiated with good results. The patient had blood loss of 4 and 6 units within 2 months and received equivolume packed RBC transfusions. Afterwards, her symptoms returned to NYHA I-II. She was successfully weaned off Flolan without worsening of her symptoms. Within 2–3 months, the patient’s symptoms and physiology of PAH recurred.
Recent research has implicated that the RBC plays an active role in pulmonary vasodilation.1,2 RBCs contain millimolar concentrations of adenosine triphosphate (ATP) and are able to release it in response to various physiological stimuli including deformation and stimulation of beta-adrenergic and prostacyclin receptors. The released ATP stimulates nitric oxide (NO) synthesis by endothelial cells and vasodilation in the pulmonary vasculature. RBCs from subjects with PAH did not release ATP in this manner and thus would fail to stimulate NO synthesis.
Knowing this background, our ability to wean the Flolan may have been associated with and due to the multiple blood transfusions replacing the patient’s defective RBCs with normally behaving ones. This would suggest that RBC “exchange transfusion” might help in acute therapy for patients who have acute exacerbations of PAH as has been done for sickle cell disease patients with acute chest syndrome. Recent genetic research has implicated the bone morphogenetic protein receptor type 2 gene (BMPR2) as a common cause for PAH. We have speculated that BMPR2 may be present on the RBC membrane, potentially linking the RBCs inability to release ATP to the genetic defect in PAH.
G.E. Liang, None.