[Measurement of exhaled nitric oxide in healthy subjects]

Endogenously synthesized nitric oxide (NO) is present in exhaled air and its analysis could be used as a tool to monitor inflammatory airway diseases. The objective of the present study was to develop the methodology for the measurement of exhaled NO and to obtain reference values in a group of healthy subjects.

Exhaled NO was measured in 40 healthy subjects and 22 asthmatic patients using a single breath manoeuvre and a chemiluminescence analyzer. Comparisons of exhaled NO while breathing both, room air and medical air, were performed in 20 subjects. In seven asthmatic patients we evaluated the effect of an inhibitor of NO-synthesis (L-NAME).

Mean (SD) exhaled NO in healthy subjects was 18 (13) parts per billion (ppb). Intraindividual variability was 6.5 (6.5%). The concentration of exhaled NO could be overestimated when environmental NO was high (> 80 ppb). Smokers showed lower levels than nonsmokers (10 [7] vs 22 [13] ppb, respectively; p < 0.005), whereas asthmatic patients showed higher exhaled NO levels (62 [31] ppb; p < 0.001). In these patients nebulization of L-NAME induced a progressive fall in exhaled NO (maximal decrease, -68 [15%]; p < 0.01).

The measurement of NO concentration in exhaled air is reproducible, not influenced by the usual levels of environmental NO, and sensible enough to detect changes induced by the administration of a specific inhibitor. Exhaled NO concentration decreases in smokers and increases in asthmatics.