A COMPARISON OF A SINGLE-STEP COLD-DRY AIR CHALLENGE AND A ROUTINE HISTAMINE PROVOCATION FOR THE ASSESSMENT OF BRONCHIAL RESPONSIVENESS IN CHILDREN AND ADOLESCENTS

Background: It has remained unclear whether bronchial responsiveness a s measured by a single-step cold-dry air challenge (CACh) correlates c losely to the responsiveness that is assessed by a routine pharmacolog ic challenge. Methods: On 2 consecutive days, we performed a CACh and a histamine challenge in 128 symptom- and medication-free pediatric an d adolescent asthma patients, The CACh consisted of 4 min of isocapnic hyperventilation of -10 degrees C, absolutely dry air; responsiveness was expressed by the induced change in FEV(1) (Delta FEV(1)). The his tamine challenge consisted of sequential inhalations of incremental in creases in concentrations of histamine; responsiveness was expressed b y the concentration which caused a 20% fall of FEV(1) (PC20). Results: Five children did not bronchoconstrict sufficiently in the histamine challenge for measuring a PC20 and were excluded from analysis. In the remaining 123, Delta FEV(1) (CACh) ranged from +5 to -73%, PC20 (hist amine) from 0.05 to 7.2 mg/mL. There was a statistically significant c orrelation between Delta FEV(1) and PC20 (r=0.54, p<0.001), but also a considerable scatter of individual data points around the regression line, Fifty-two subjects were hyperresponsive by CACh and 114 by hista mine criteria. Conclusions: There is a relatively weak correlation bet ween the results of these two challenges; thus, one cannot be substitu ted one for the other, Histamine appears as more sensitive in detectin g airway hyperresponsiveness than CACh, The poor correlation between t he responses to these two challenges can be explained by differences b etween the challenge protocols, or, alternatively, by differences betw een applied stimuli and activated mechanisms.