Exhaled Nitric Oxide Is Age-Dependent in Asthma

We determined whether the exhaled nitric oxide (eNO) level in asthmatics is age-dependent. Eighty-seven asthmatic patients aged 2-41 years were studied. Hyperreactivity to adenosine 5′-monophosphate (AMP) was used to confirm asthma (≤200 mg/ml). In the younger group of children (2-5 years), AMP challenge was performed by the provocation concentration causing wheeze (PCW) method, while in the older groups of patients (6-41 years), regular spirometry was used. Exhaled NO was measured in the younger group by the tidal breathing method (TBm) and in the older subjects by the slow vital capacity method (SVCm). TBm and SVCm were compared in 21 other subjects, and there was a significant correlation between the two values (r = 0.96, P < 0.0001). The equation of correlation between the two methods was eNO TBm = 0.78eNOSVCm - 0.51. Within asthmatic patients, we found a significant increase in eNO with age (P < 0.0001), while there was no significant difference in AMP reactivity (P = 0.35). We conclude that eNO in asthmatic patients is age-dependent, with lower values in young children.