EXHALED NO DURING GRADED CHANGES IN INHALED OXYGEN IN MAN

Background - Nitric oxide (NO) is present in the exhaled air of animal s and humans. In isolated animal lungs the amount of exhaled NO is dec reased during hypoxia. A study was undertaken to determine whether cha nges in arterial oxygen tension affect levels of exhaled NO in humans. Methods - Sixteen healthy subjects were randomised to inhale differen t gas mixtures of oxygen and nitrogen in a double blind crossover stud y. Eight gas mixtures of oxygen and nitrogen (fractional inspired oxyg en concentration (Fio(2)) 0.1 to 1.0) were administered. Exhaled NO wa s measured with a chemiluminescence detector from end expiratory singl e breath exhalation. Results - A dose-dependent change in exhaled NO d uring graded oxygen breathing was observed (p = 0.0012). The mean (SE) exhaled NO concentration was 31 (3) ppb at baseline, 39 (4) ppb at an Fio(2) of 1.0, and 26 (3) ppb at an Fio(2) of 0.1. Conclusions - The NO concentration in exhaled air in healthy humans is dependent on oxyg en tension. Hyperoxia increases the level of exhaled NO, which indicat es increased NO production. The mechanism behind this phenomenon remai ns to be elucidated.