Hyperventilation with cold versus dry air in 2- to 5-year-old children with asthma

UNLABELLED: Cold air challenge (CACh) has been shown to discriminate between children with asthma and healthy young children. Hyperventilation with dry room-temperature air is a simplified alternative. We compared responsiveness in young children with asthma between two standardized, single-step protocols: dry air challenge (DACh) performed as 6 minutes of eucapnic hyperventilation with dry room-temperature air and CACh as 4 minutes of hyperventilation. Response was measured as specific airway resistance by whole-body plethysmography and expressed as change from baseline in numbers of within-subject SDs (SDw). The challenge sequence was randomly assigned. A comparator challenge was performed 1 hour later if the first challenge gave a change of 3 SDw or more. Forty 2- to 5-year-old children with asthma were included. Responsiveness to cold versus dry air showed significant, but weak, correlation (r(2) = 0.34, p < 0.0001), but responsiveness to CACh exceeded DACh (7.6 vs. 5.4 SDw, p < 0.02). CACh seemed to induce reduction in response to the following DACh (p < 0.01), whereas no such reduction was seen after DACh.

CONCLUSION: Responsiveness to CACh exceeded responsiveness to DACh, and CACh seemed to induce refractoriness in contrast to DACh, probably because of the additional stimulus from airway cooling. This finding suggests CACh as the preferred method of challenge.