age >17

pulmonary arterial hypertension (pah) associated with who group 1 who start a parenteral prostanoid-therapy

written informed consent

prostanoid naive

no change of the pah specific therapy within 3 weeks of the recruitment to the study

pregnancy and lactation period

women of child bearing potential who do not use an effective and secure method for birth control

severe chronic kidney insufficiency (glomerular filtration rate <30), which will remain for more than 3 months

liver-insufficiency child c

life expectancy shorter than the course of the study (for example because of malignant disease