INHALED NITRIC-OXIDE REVERSES HYPOXIC PULMONARY VASOCONSTRICTION IN DOGS - A PRACTICAL NITRIC-OXIDE DELIVERY AND MONITORING-SYSTEM

Nitric oxide (NO) is a potent dilator of vascular smooth muscle that l ikely represents an important endothelium-dependent relaxing factor. R ecent interest has focused on inhaled NO as a pulmonary vasodilator. T he purpose of this study was to design a reliable NO delivery system w ith on-line monitoring of NO and nitrogen dioxide (NO2) concentrations , and to test the effects of inhaled NO in a dog model of acute hypoxi c pulmonary vasoconstriction (HPV). Six canines were studied. Marked H PV was induced using a hypoxic gas mixture. Using a standard blender, NO was delivered through a volume-cycled ventilator. We were able to r apidly adjust the delivered NO concentration using this system. An on- line chemoluminescence analyzer was used to continuously measure NO an d NO2 concentrations. Inhaled NO at 40 and 80 ppm for 30 min rapidly r eversed HPV in all animals (PVR 502 +/- 154 dynes.s.cm(-5) with hypoxi a, 244 +/- 52 with 40 ppm NO, 227 +/- 47 with 80 ppm NO). No significa nt NO2 or methemoglobin production was noted during the study. We conc lude that inhaled NO can be easily delivered through a ventilator and the dose rapidly adjusted, NO and NO2 concentrations can be monitored continuously on-line, inhaled NO rapidly reverses HPV in dogs, and wit h short-term NO inhalation, there is no significant NO2 or methemoglob in formation. Inhaled, NO may, therefore, have a future clinical role as a new agent in the diagnosis and treatment of other forms of pulmon ary hypertension.