Effects of oxygen and nitric oxide inhalation in a porcine model of recurrent microembolism

Background: Inhalation of nitric oxide (iNO) has been proposed for the trea tment of acute pulmonary embolism. The present study evaluates the effects of oxygen (O-2) and nitric oxide inhalation in a porcine model of sustained pulmonary hypertension induced by recurrent pulmonary microembolism. Methods: Twelve pigs were embolized under general anesthesia with 300-mu m microspheres intravenously three times over a period of seven weeks. Five p igs served as untreated controls. Hemodynamic and gas exchange responses to 100% oxygen and 40 ppm NO inhalation, and their combination (O-2+iNO) were measured seven days after the last embolization. Results: Recurrent microembolism caused sustained pulmonary hypertension (p ulmonary Vascular resistance index; PVRI 408+/- 57 dyn.s.cm(-1).m(-2)) as c ompared to the control group (PVRI 143+/-20 dyn.s.cm(-5).m(-2); P<0.05). PV RI was significantly reduced by O-2, iNO, and O-2 + iNO inhalation by 29 +/ - 3, 28 +/- 4, and 32 +/- 3%, respectively. Conclusion: We conclude that both O-2 and iNO are selective pulmonary vasod ilators in a porcine model of sustained pulmonary hypertension following re current pulmonary microembolism and, therefore, may be useful in the treatm ent not only in the acute phase of pulmonary embolism but also later in the time course of the disease.