Differential flow analysis of exhaled nitric oxide in patients with asthma of differing severity

The majority of asthmatic patients achieve control of their illness; others do not. It is therefore crucial to validate/develop strategies that help the clinician monitor the disease, improving the response to treatment.

We have quantified the inflammation in central and peripheral airways by measuring exhaled nitric oxide (NO) at multiple exhalation flows in 56 asthmatics at different levels of severity (mild, n = 10; moderate stable, n = 17; moderate during exacerbation, n = 11; severe, n = 18, 7 of whom were receiving oral corticosteroids) and 18 healthy control subjects. The reproducibility of the measurement was also assessed.

Bronchial NO (Jno) in patients with mild asthma (2,363 +/- 330 pL/s) [mean +/- SD] was higher than in patients with moderate stable asthma (1,300 +/- 59 pL/s, p < 0.0005), in patients with severe asthma receiving inhaled corticosteroids (ICS) [1,015 +/- 67 pL/s, p < 0.0005], and healthy control subjects (721 +/- 22 pL/s, p < 0.0001). There were no differences between Jno in patients with mild asthma compared to patients with severe asthma receiving ICS and oral corticosteroids (2,225 +/- 246 pL/s). Patients with exacerbations showed a higher Jno (3,475 +/- 368.9 pL/s, p < 0.05) compared to the other groups. Alveolar NO was higher in patients with severe asthma receiving oral corticosteroids (3.0 +/- 0.1 parts per billion [ppb], p < 0.0001) than in the other groups but was not significantly higher than in patients with moderate asthma during exacerbation (2.8 +/- 0.3 ppb). No differences were seen in NO diffusion levels between the different asthma groups. All the measurements were highly reproducible and free of day-to-day and diurnal variations.

Differential flow analysis of exhaled NO provides additional information about the site of inflammation in asthma and may be useful in assessing the response of peripheral inflammation to therapy.