Pulmonary NO synthase inhibition and inspired CO2: effects on V ’/Q ’ and pulmonary

ABSTRACT: Inhaled carbon dioxide decreases ventilation/perfusion ratio (V ’/Q ’) heterogeneity in dogs. The aim of this study was to test whether inhaled CO2 improves the V ’/Q ’ by inhibition of nitric oxide production and whether inhibition of endo-genous NO production in the lung alters gas exchange and V ’/Q ’ matching. Eleven healthy dogs were anaesthetized and mechanically ventilated. The multiple inert gas elimination technique (MIGET) was used to measure V ’/Q ’ heterogeneity and regional pulmonary blood flow heterogeneity was assessed in five dogs using fluorescent microspheres. In a separate set of five dogs, exhaled NO levels were mea-sured via chemiluminescence. All dogs were studied before and after 4.8 % inspired CO2, and then given the NO synthase inhibitor N v-nitro-L-arginine methyl ester (L-NAME, 10 mg.kg-1) via nebulization, after which they were studied again with room air and inhaled CO2. CO2 and L-NAME improved arterial and alveolar oxygen tension, but the im-provements with L-NAME did not reach statistical significance. Improved V ’/Q