EXHALED NITRIC-OXIDE IS HIGHER BOTH AT DAY AND NIGHT IN SUBJECTS WITHNOCTURNAL ASTHMA

Nitric oxide in exhaled air is thought to reflect airway inflammation. No data have been reported so far on circadian changes in NO in subje cts with nocturnal asthma. To determine whether exhaled NO shows a cir cadian rhythm inverse to the circadian rhythm in airway obstruction in subjects with nocturnal asthma, we conducted a study involving six he althy controls, eight individuals without nocturnal asthma (4-h to 16- h variation in peak expiratory flow [PEF] less than or equal to 15%), and six individuals with nocturnal asthma (4-h to 16-h PEF variation > 15%). Smoking, use of corticosteroids, and recent respiratory infecti ons were excluded. NO concentrations were measured at 12, 16, 20, and 24 h, and at 4, 8, and 12 h of the next day, using the single-breath m ethod. At the same times, FEV1 and PEF were also measured. Mean NO con centrations were significantly higher in subjects with nocturnal asthm a than in subjects without nocturnal asthma, and higher in both groups than in healthy controls at all time points. Mean exhaled NO levels o ver 24 h correlated with the 4-h to 16-h variation in PEF (r = 0.61, p < 0.01). Exhaled NO did not show a significant circadian variation in any of the three groups as assessed with cosinor analysis, in contras t to the FEV1 in both asthma groups (p < 0.05). At 4 h, mean +/- SD NO levels were higher than at 16 h in subjects with nocturnal asthma; at 50 +/- 20 ppb versus 42 +/- 15 ppb (p < 0.05); other measurements at all time points were similar. Differences in NO and FEV1 from 4 h to 1 6 h did not correlate with one another. We conclude that subjects with nocturnal asthma exhale NO at higher levels both at night and during the day, which may reflect more severe diurnal airway-wall inflammatio n. A circadian rhythm in exhaled NO was not observed. NO levels did no t correspond to the circadian rhythm in airway obstruction. The small increase in NO at 4 h may indicate an aspect of inflammation, but it i s not associated with increased nocturnal airway obstruction.