Exhaled nitric oxide (eNO) is a noninvasive marker of airway inflammation in asthma.Spirometry, impulse oscillometry, and eNO measurements were performed before and after methacholine inhalation challenge (bronchoconstriction phase) and after beta2-agonist inhalation (bronchodilation phase) in 62 children with asthma, 13 "wheezy" children, and 17 healthy children.
A significant decrease occurred in the eNO level after methacholine inhalation challenge. This decrease did not correlate with the percentage decrease in forced expiratory volume in 1 second (FEV1) but it did correlate with the percentage decline in maximal expiratory flow at 50% vital capacity and with the change in small airway resistance.
eNO recovered to the previous level immediately after beta2-agonist inhalation.
The study authors concluded that the eNO level decreases after methacholine inhalation challenge. This decrease primarily depends on bronchoconstriction of the small airways.
Inflammation in asthma (mind map). FeNO is a marker of oxidative stress. See more Allergy and Immunology mind maps here.
If methacholine challenge is negative but FeNO is higher than 30 ppb, perform adenosine challenge to rule out asthma (Ann of Allergy and Imm, 2012).
References:
Effect of bronchoconstriction on exhaled nitric oxide levels in healthy and asthmatic children. Tadaki H, Mochizuki H, Muramastu R, Hagiwara S, Takami S, Mizuno T, Arakawa H. Ann Allergy Asthma Immunol. 2009 Jun;102(6):469-74.
Exhaled nitric oxide correlated with control in recurrent infantile wheeze treated with inhaled corticosteroids. http://goo.gl/AS7I
Methacholine not as sensitive to diagnose asthma as previously thought, Medscape, 2011. http://goo.gl/ajn0S
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