Effects of intermittent inhalation of nitric oxide on plasma nitric oxide concentration in the systemic circulation *
Background:Inhalation of nitric oxide（INO）plays a role as a selective pulmonary vasodilator, and improvement of oxygenation has been used for patients with pulmonary hypertension and acute respiratory distress syndrome（ARDS）. Intermittent INO is monitored clinically to reduce any side effects and to prevent a ventilation-perfusion mismatch. Although inhaled NO has been considered to be rapidly oxidized and inactivated in the pulmonary circulation, it has recently been suggested that INO influenced by NO dynamics in the systemic circulation. Therefore, it has been proposed that repeatedly administered NO may affect NO dynamics in the systemic circulation. Therefore, we present the results of direct measurement of plasma NO concentration in the systemic circulation with an NO-selective sensor for in vivo measurement during intermittent INO. METHODS:An NO sensor was introduced through a 5 Fr sheath into the carotid artery and the left femoral artery in anesthetized pigs（n＝７）. The tip of the NO sensor was positioned in the aortic arch and the left illiac artery. NO（1 ppm）was inhaled through an INO device from a respirator. NO was inhaled four times intermittently for 15 minutes with an INO rest phase of 15 minutes between inhalation period. RESULTS:When NO was inhaled four times intermittently, the base-to-peak changes in the plasma NO concentrations in the aortic arch and the left illiac artery were observed reproducibly in both regions（respectively, first time:0.9±0.8nM, 0.1±0.9nM, second time:1.4±1.0nM, 1.1±1.0nM, third time:1.1±1.0nM, 0.5±1.0nM, fourth time:1.5±1.1nM, 0.7±0.8nM）. There were no significant differences in the base-to-peak changes in the plasma NO concentrations between in the aortic arch and the left illiac artery as well as between different NO inhalation repeating numbers. Heart rate and aortic pressure were not changed significantly by INO. CONCLUSIONS:The change in the plasma NO concentration in the systemic circulation during intermittent INO could be measured stably by the NO sensor. The plasma NO concentration was shown to increase reproducibly during the intermittent INO not only in the aortic arch but also the illiac artery of the more peripheral circulation. Thus, it is suggested that the plasma NO concentrations in the arteries during the intermittent INO increase reproducibly and that inhaled NO affect the NO dynamics in the systemic circulation.（Accepted on October 22，2007)
