Effect of natural grass pollen exposure on exhaled nitric oxide in asthmatic children

Exhaled nitiric oxide (NO) is increased in exhaled breath of asthmatic pati ents. The aim of this study was to investigate the longitudinal changes of exhaled NO outside and during the pollen season in pollen-allergic asthmati c children. Twenty-one children (age 6 to 16 yr), with a seasonal allergic asthma sensitive to grass pollen, underwent measurements of exhaled NO and pulmonary function before (March), during (May), and after (November) the p ollen season. Exhaled NO was measured by a tidal breathing method with a ch emiluminescence analyzer and NO steady-state levels were recorded. The timi ng of the measurements during the pollen season was based on the atmospheri c pollen count. Exhaled NO values of asthmatic children were compared with those of 21 sex- and age-matched healthy children. Pulmonary function and s ymptoms of asthma were also evaluated at each visit. The mean value of exha led NO before the grass season was 12.7 +/- 5.1 ppb (mean +/- SD), signific antly higher when compared with controls (7.8 +/- 2.7 ppb, p < 0.001). In t he pollen season there was a significant (p < 0.001) twofold increase in ex haled NO (21.4 +/- 7.6 ppb) that, after the season, returned to values simi lar (12.8 +/- 5.8 ppb, p = NS) to those found before the season. There were no significant changes in FEV1 before and during the season (98.6% predict ed versus 101% predicted, p = NS). We conclude that natural allergen exposu re is related to an increase of exhaled NO in asthmatic grass pollen-allerg ic children even in absence of significant changes in airways function. We speculate that measurement of exhaled NO could be a sensitive noninvasive m arker of asthma disease activity.