Correlation between reversibility of airway obstruction and exhaled nitric oxide levels in children with stable bronchial asthma

Recent trials measuring exhaled nitric oxide (eNO) concentrations have suggested that it may be a useful measure of ongoing airway inflammation in patients with asthma. The purpose of this study was to examine the relationship between eNO levels and baseline as well as postbronchodilator spirometry, a measurement commonly used in the clinical setting to determine the severity of asthma and as a guide to therapeutic decisions. Forty-nine patients between the ages of 5-16 years with physician-diagnosed asthma who attended the pediatric pulmonary clinic for a routine asthma visit with spirometric evaluation were recruited for the study. eNO levels prior to spirometry were obtained before and after receiving inhaled beta(2) agonist. eNO samples were collected in impermeable bags (Tedlar) and assayed within 24 hr by chemiluminescence. Regression analysis was used to assess the relationships between pre- and postbronchodilator eNO and spirometric variables. eNO was also compared in patients receiving and not receiving inhaled corticosteroids (ICS), as well as those whose therapy had been increased after evaluation by a pediatric pulmonologist or allergist. We found no significant difference between the levels of eNO before and after inhalation of beta(2) agonist (P = 0.60 paired t-test). Positive correlation was found between eNO vs. percentage change in FEV(1) (r = 0.35, P = 0.01) and percentage change in FEF(25-75% )(r = 0.29, P = 0.04). A negative correlation was found between prebronchodilator FEV(1) and eNO (r = -0.29, P = 0.03). Patients on ICS had lower mean eNO levels (29.9 vs. 47.6 parts per billion (ppb), P = 0.053) than those not receiving ICS. Patients whose ICS therapy was increased had higher mean eNO levels (47.2 vs. 26.9 ppb, P = 0.018) than those not having ICS therapy increased. We suggest that eNO levels could be a clinically useful measurement of asthma severity and could be used as an adjunct to spirometry to determine appropriate treatment plans. Longitudinal clinical trials are needed to determine if eNO can enhance therapeutic decisions for asthmatic children.