Effect of inhaled nitric oxide on the hypoxic pulmonary vasoconstrictor response in anaesthetised calves

The effect of inhaling nitric oxide in the hypoxic pulmonary vascular response was measured in five calves anaesthetised with a combination of guaiacol, ketamine and xylazine. Alveolar hypoxia was induced by means of the inhalation of a gas mixture with an inspiratory oxygen fraction of 14-18 per cent. This alveolar hypoxia resulted in a pronounced pulmonary hypertension (mean pulmonary artery pressure in hypoxic animals: 30.2 mmHg). Inhalation of 20 and 40 ppm of nitric oxide significantly attenuated the hypoxia induced pulmonary hypertension. The effect ceased once nitric oxide administration was stopped. A concentration of 40 ppm of nitric oxide fully abolished the hypoxia induced pulmonary hypertension (mean pulmonary artery pressure during inhalation of 40 ppm nitric oxide: 22.8 mmHg). Inhalation of nitric oxide had no effect on systemic arterial blood pressure nor on systemic vascular resistance. It was concluded that inhalation of 20 or 40 ppm of nitric oxide prevented a selective pulmonary vasoconstriction during alveolar hypoxia in calves, which may be helpful in the treatment of acute respiratory disorders in calves.