Short-term variability of exhaled nitric oxide in young male patients with mild asthma and in healthy subjects

Abstract

Background: Exhaled nitric oxide (NO exp) is an indicator of eosinophilic airways inflammation. This study evaluated short-term variability of NO exp in 13 healthy subjects (19–41 years, eight males) and in 31 patients with asthmatic respiratory symptoms (19–21 years, all male) to obtain data for assessment of short-term changes of NO exp in clinical situations. Methods: Mild asthma was confirmed in 10 patients (Group = asthma). Twenty-one patients with asthmatic respiratory symptoms did not fulfill the functional criteria of asthma (Group = respiratory symptoms). The procedure to determine NO exp followed the European Respiratory Society (ERS) guidelines; the mean expiratory flow used during sampling was 0.09—0.12 l/s. NO exp for each subject was determined as the mean of at least three successive measurements at the baseline, followed by determinations at 10 min, 6 h and 24 h after the baseline. Results: At the baseline, the mean ( sd) value of NO exp was 6.6 (2.3) parts per billion (ppb) in the healthy controls, and significantly higher both in patients with respiratory symptoms (14.6 (11) ppb, P = 0.0076) and in those with asthma (34.2 (43) ppb, P<0.001). Intra-class correlation coefficient of NO exp measured at baseline and after an interval of 10 min was 0.959 in healthy subjects, 0.986 in patients with respiratory symptoms and 0.936 in asthma patients, respectively. Short-term variability in terms of coefficient of variation (Co V) of repeated measurements of NO exp at 10 min, 6 h and 24 h was 5.1, 10.8 and 11.7% in healthy subjects, 7.1, 16.4 and 22.2% in patients with respiratory symptoms and 13.5, 19.4 and 26.4% in asthma patients, respectively. Conclusions: Reproducibility of NO exp using standardized methods was good both in healthy subjects and in asthmatic patients. However, in asthmatics the short-term variation of NO exp was over two times as high as in healthy subjects. The level of NO exp was elevated, except in asthma, also in patients with asthmatic respiratory symptoms who did not fulfill the functional criteria of asthma.