Background: Exhaled nitric oxide (eNO) has recently been proposed to be a noninvasive marker of airway inflammation in asthma.
Objective: To evaluate the effect of bronchoconstriction by means of methacholine inhalation challenge on levels of eNO in children.
Methods: Spirometry, impulse oscillometry, and eNO measurements were performed before and after methacholine inhalation challenge (bronchoconstriction phase) and after beta2-agonist inhalation (bronchodilation phase) in 92 children (62 children with asthma, 13 wheezy children, and 17 healthy children).
Results: A significant decrease occurred in the eNO level after methacholine inhalation challenge (P < .01). This decrease did not correlate with the percentage decrease in forced expiratory volume in 1 second or with the change in large airway resistance (R20), but it did correlate with the percentage decline in maximal expiratory flow at 50% vital capacity and with the change in small airway resistance (R5-R20). The eNO decrease lasted for 15 minutes after beta2-agonist inhalation in the group with a high percentage decrease in R5-R20 (>200%). On the other hand, in the group with a low percentage decrease in R5-R20 (< or =200%), eNO recovered to the previous level immediately after beta2-agonist inhalation.
Conclusions: The eNO level significantly decreases after methacholine inhalation challenge. This decrease primarily depends on bronchoconstriction of the small airways.