Effect of bronchoconstriction on exhaled nitric oxide levels in healthy and asthmatic children

Abstract

Exhaled nitric oxide (eNO) has recently been proposed to be a noninvasive marker of airway inflammation in asthma. To evaluate the effect of bronchoconstriction by means of methacholine inhalation challenge on levels of eNO in children. 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). 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. The eNO level significantly decreases after methacholine inhalation challenge. This decrease primarily depends on bronchoconstriction of the small airways.