Reduction of hypoxic pulmonary vasoconstriction by nitrous oxide administration in the isolated perfused cat lung.

Local pulmonary vasconstriction in response to alveolar hypoxia is a protective mechanism reducing blood flow to poorly oxygenated areas of lung. Pulmonary blood flow is thereby directed to better oxygenated lung units and venous admixture and the resulting arterial hypoxaemia is reduced. The effect of nitrous oxide on the pulmonary pressor response to alveolar hypoxia was assessed in the isolated perfused cat lung preparation under conditions of constant flow and constant left atrial and airway pressures. Nitrous oxide, in concentrations of 50 per cent and 75 per cent, was found to produce a reversible depression of the hypoxic pulmonary pressor response. The importance of hypoxia pulmonary vasconstriction and the possible implications of its reduction by anaesthetic agents are discussed.