Background: It has remained unclear whether bronchial responsiveness as measured by a single-step cold-dry air challenge (CACh) correlates closely to the responsiveness that is assessed by a routine pharmacologic challenge.
Methods: On 2 consecutive days, we performed a CACh and a histamine challenge in 128 symptom- and medication-free pediatric and 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 FEV1 (delta FEV1). The histamine challenge consisted of sequential inhalations of incremental increases in concentrations of histamine; responsiveness was expressed by the concentration which caused a 20% fall of FEV1 (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 FEV1 (CACh) ranged from +5 to -73%, PC20 (histamine) from 0.05 to 7.2 mg/mL. There was a statistically significant correlation between delta FEV1 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 histamine criteria.
Conclusions: There is a relatively weak correlation between the results of these two challenges; thus, one cannot be substituted one for the other. Histamine appears as more sensitive in detecting airway hyperresponsiveness than CACh. The poor correlation between the responses to these two challenges can be explained by differences between the challenge protocols, or, alternatively, by differences between applied stimuli and activated mechanisms.