Inhalation of a nitric oxide synthase inhibitor to a hypoxic or collapsed lung lobe in anaesthetized pigs: effects on pulmonary blood flow distribution.

I.v. administration of the nitric oxide synthase inhibitor, nitro-L-arginine methyl ester (L-NAME), not only reduces blood flow in a hypoxic lung region but also causes systemic vasoconstriction and a decrease in cardiac output. In this study, we delivered nebulized L-NAME 0.2-1 mg kg-1 to the left lower lobe of 10 anaesthetized pigs. The left lower lobe was made hypoxic by selective inhalation of 5% oxygen or collapsed by interrupted ventilation, or both. Inhalation of L-NAME reduced fractional blood flow to the left lower lobe from 5.3 (SD 3.1)% to 1.7 (1.4)% (P < 0.05) in lobar hypoxia and from 6.0 (3.3) to 2.7 (2.7)% (P < 0.05) in lobar collapse. These reductions were accompanied by a significant increase in PaO2. There were no significant changes in arterial pressure, cardiac output or heart rate. We have shown that selective inhalation of L-NAME reduced blood flow to a hypoxic or collapsed lung region without systemic effects. The possible role for nitric oxide synthase inhibition in reducing shunt during one-lung ventilation, however, requires further study.