THE EFFECTS OF NITRIC-OXIDE INHALATION ON THE PULMONARY CIRCULATION OF PRETERM LAMBS

This study was designed to test the hypothesis that inhalation of nitr ic oxide by lambs delivered prematurely would result in increased syst emic arterial blood oxygen tension and decreased pulmonary vascular re sistance. Eleven premature fetal lambs were delivered by cesarean sect ion at 126-127 d gestation. One hundred min after the onset of ventila tion, nitric oxide gas was added to the lambs' breathing mixture. The animals were exposed in random order to 5 ppm for 10 min, 20 ppm for 1 0 min, and 20 ppm for 20 min. Each treatment period was preceded by an d followed by a 10-min washout period. When compared with the washout (control) periods, all three treatment periods resulted in an improvem ent in both the systemic arterial blood oxygen tension and the physiol ogic intrapulmonary shunt. Inhalation of nitric oxide also resulted in a selective decrease in pulmonary arterial blood pressure. Comparison s between the different treatment groups revealed a further improvemen t in blood oxygenation and pulmonary hemodynamics when using the highe r concentration of nitric oxide. Interestingly, the rise in arterial b lood oxygenation continued after inhaling 20 ppm nitric oxide for more than 10 min.