INHALATION OF NITRIC-OXIDE MODULATES ADULT HUMAN BRONCHIAL TONE

We studied whether nitric oxide (NO), added at 80 ppm to inspired gas, can exert a bronchodilatory effect in humans. Four groups were studie d: (1) healthy adult volunteers (n = 6), (2) adult subjects with hyper reactive airways(n = 6) during provocation with inhaled methacholine ( MCh), (3) patients with bronchial asthma (n = 13), and (4) patients wi th chronic obstructive pulmonary disease (COPD, n = 6). All subjects w ere studied in a body plethysmograph, measuring volume-corrected speci fic airway conductance (SGaw). No patient or volunteer reacted with br onchoconstriction during NO inhalation. Nitric oxide did not affect SG aw in healthy volunteers or in patients with COPD. Inhaled NO modulate d the MCh-induced bronchoconstriction toward dilatation. In patients w ith bronchial asthma, SGaw increased (p < 0.05) from 0.4 +/- 0.1 to 0. 6 +/- 0.2 (kPa.s)(-1) In a succeeding test with inhalation of a beta(2 )-agonist immediately after NO inhalation, a more marked increase in S Gaw was seen, to 1.2 +/- 0.3 (kPa.s)(-1) (p < 0.001). We conclude that NO inhaled at 80 ppm has no effect on airway tone in healthy voluntee rs, but modulates the response to MCh provocation toward bronchodilati on. It exerts a weak bronchodilatory effect in bronchial asthma, but n ot in COPD.