Aims: Endothelial dysfunction is likely to contribute to the pathogenesis of idiopathic Pulmonary Arterial Hypertension (iPAH). We hypothesize that there are different patterns of endothelial cell function, which we studied in 17 children with iPAH.
Methods and results: Pulmonary flow reserve was determined by acetylcholine infusion into segmental pulmonary arteries utilizing quantitative angiography and intra-arterial Doppler flow wire. Depending on the reactivity of the pulmonary to systemic arterial pressure ratio to short-term oxygen and intravenous epoprostenol or aerosolized iloprost responders and nonresponders were classified. In 7 responders to oxygen-prostanoid administration the pressure ratio decreased from 0.9 +/- 0.2 to 0.31 +/- 0.11 (p = 0.01), the mean pulmonary flow reserve showed an excessive increase to 3.6 +/- 2.0 (p = 0.01) after infusion of acetylcholine. In 10 non-responders the pressure ratios remained unchanged during oxygen-prostanoid testing. 4 of 5 patients without any effect to acetylcholine died despite long-term epoprostenol treatment. The other 5 nonresponders to oxygen-prostanoid showed an impaired but significant increase of the pulmonary flow reserve of 1.6 +/- 1.1 (p = 0.01). 2 of these patients did not only improve clinically, but regained vascular reactivity by additional therapy with sildenafil.
Conclusion: Endothelial reactivity in iPAH is either extensive, impaired or absent. Acetylcholine infusion casts a light on the pathogenesis and has implications for therapy.