The effect of N(G)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, on respiratory mechanics in rats.

BACKGROUND Data describing the inhibitory effects of nitric oxide synthase (NOS) on respiratory mechanics are conflicting, and no data are available concerning possible effects on the viscoelasticity of the respiratory system, on the inspiratory work of breathing (WOB) or on respiratory system hysteresis. OBJECTIVES The aim of this study was to measure the effects of NOS inhibition by N(G)-nitro-L-arginine methyl ester (L-NAME) on respiratory mechanics in normal anesthetized rats. METHODS Using the end-inflation occlusion method, it was possible to quantify the ohmic and viscoelastic airway resistance and elastance of the respiratory system. Ohmic resistance is the normalized-to-flow pressure dissipation due to viscous forces opposing the airflow in the airways, as predicted by the Poiseuille law. Viscoelastic resistance is the normalized-to-flow pressure dissipation due to the resistance of respiratory system tissue to deformation during inflation, which is recovered after the arrest of the inspiratory flow (stress relaxation). The inspiratory WOB, its elastic and resistive components, and hysteresis were also calculated. RESULTS L-NAME induced an increment in the ohmic airway resistance and in the resistive ohmic inspiratory WOB. The viscoelastic resistance due to stress relaxation and the elastic properties of the respiratory system were not modified, and no effect was detected on the related components of the inspiratory WOB and on hysteresis. CONCLUSIONS NO acts in normal rats to reduce the ohmic component of airway resistance, decreasing the ohmic inspiratory WOB. The elastic and viscoelastic components are unaltered. Hysteresis is also unaltered, suggesting that NO has negligible effects on alveolar surfactant activity.