[Reproducibility of the technique for measuring nitric oxide in exhaled air in healthy subjects]

Exhaled nitric oxide (NO) has become established as the principal non-invasive marker of airway inflammation. Exhaled NO levels reported in the literature vary greatly, with differences sometimes attributable to measurement technique.

To determine the reproducibility of the technique used by our department to measure exhaled NO and to know whether results vary with diet and patient characteristics.

We studied 20 healthy subjects (10 men and 10 women; mean age 28.21 years). Exhaled NO was measured when the patient was fasting(N1), 30 minutes after intake of vegetables (N2) and 30 minutes after intake of meat/fish (N3). For each measure N1, N2 and N3 we took the average of three consecutive measurements separated by 10 minutes. Exhaled NO was assessed by controlled-flow chemoluminescence after adjusting for trapped air and after generating pressure in the oral cavity that was sufficient to close the soft palate(Eco Physics CLD 77 AM analyzer).

The mean concentration was 3.40 1.30 ppb for N1, 4.03 1.00 ppb for N2 and 3.71 1.05 ppb for N3. The differences between measurements were not statistically significant(p > 0.05). Nor were differences between the sets of three measurements significant. The mean concentration was 3.13 0.41 ppb for women and 3.72 0.31 ppb for men (ns). No significant differences were related to body mass index 25 (n = 15) or > 25 (n = 5).

The technique our department uses for measuring exhaled NO is reproducible and differences are unrelated to food intake, sex or body mass index.