Inhaled nitric oxide selectively reverses the hypoxic pulmonary vasoconstrictor response in calves

The effect of inhaling nitric oxide on the hypoxic pulmonary vasoconstrictor response in calves was evaluated. In five healthy, anaesthetised Friesian Holstein calves alveolar hypoxia was induced by means of the inhalation of a gas mixture with an inspiratory oxygen fraction of 14 - 18 %. This alveolar hypoxia resulted in a pronounced pulmonary hypertension. The inhalation of 20 and 40 ppm of nitric oxide induced a significant fall of the hypoxic pulmonary hypertension. A concentration of 40 ppm of nitric oxide was needed to fully abolish the induced pulmonary hypertension. The inhalation of nitric oxide had no effect on the systemic arterial pressure nor on the systemic vascular resistance. It was concluded that the inhalation of nitric oxide resulted in a selective pulmonary vasodilatation during alveolar hypoxia in calves