VIP and pulmonary arterial hypertension: Moreover, in an open-label study, a total of 20 patients with pulmonary hypertension (PAH in nine, secondary to lung disease in eight, and chronic thromboembolic in three) inhaled a single 100-μg dose of vasoactive intestinal peptide during right-heart catheterization, which caused significant selective pulmonary vasodilation with improved stroke volume and mixed venous oxygen saturation [91].