EXPIRED NITRIC-OXIDE AFTER BRONCHOPROVOCATION AND REPEATED SPIROMETRYIN PATIENTS WITH ASTHMA

Compared with normal individuals, subjects with asthma have elevated l evels of expired nitric oxide (NO). These levels are hypothesized to r eflect the degree of airway inflammation. Expired NO levels rise durin g the late phase of allergen challenge and decrease in asthmatics afte r steroid treatment. Isocapnic cold air hyperventilation (ISH) is beli eved to cause airway narrowing through noninflammatory mechanisms. We measured mixed expired NO in 10 individuals with atopic asthma who und erwent both ISH challenge and allergen challenge, and compared these m easurements with the change in expired NO that occurred after serial s pirometry alone. We found that ambient NO levels affected mixed expire d NO. Controlling for inspired NO, we found that repeated spirometry a lone produced a significant fall in mixed expired NO (p < 0.01) that w as maximal after 30 min (36.6 +/- 8.5% fall). After allergen and ISH c hallenges, expired NO was elevated relative to levels after repeated s pirometry (p < 0.01 and p = 0.065, respectively). In addition, we foun d that prechallenge expired NO levels were significantly correlated wi th the magnitude of the late fall in FEV, following allergen challenge (r = 0.80, p < 0.01). These data demonstrate that repeated spirometry results in reduced mixed expired NO and suggest that both ISH and all ergen-induced bronchoconstriction share pathobiologic mechanisms that produce increases in mixed expired NO.