Cold air challenge of airway hyperreactivity in children: Dose-response interrelation with a reaction plateau

A previous study of cold air challenge (CACh) in children with asthma produced indirect evidence for the existence of a reaction plateau. To examine directly this phenomenon, 17 children, mean age 13/2 years, were challenged by isocapnic hyperventilation with −10° C air at 75% of maximal voluntary ventilation for 10 minutes (extended CACh [ECACh]). Each minute FEV 1 and maximum expiratory flow at 25% remaining vital capacity (V 25 ) were measured. During "recovery" these measurements were repeated every minute for 10 minutes. Analysis of the cumulative dose-response curves constructed from the measurements revealed that a reaction plateau was reached in the last minutes of the challenge by both functions in each child. Induced changes in absolute terms were similar for both functions (FEV 1 : −28 ± 12% predicted; V 25 : −29 ± 17% predicted), but V 25 started at a lower baseline (FEV 1 : 81 ± 15% predicted; V 25 : 48 ± 27% predicted) and thus arrived at a higher degree of obstruction (FEV 1 : 53 ± 19% predicted; V 25 : 19 ± 13% predicted). Together with the reaction plateau developing faster for V 25 , this indicated a dose-response influenced by baseline small airway obstruction. Although the size of the reaction differed from one child to the other (FEV 1 : −5% to −50% predicted; V 25 : −4% to −77% predicted), interindividual variability in the development of the reaction decreased toward the end of the challenge and was minimal at the plateau and in the early minutes of "recovery." Repeating ECACh after 10 days demonstrated intraindividual variability also being minimal at the plateau and in early "recovery." A brief uninterrupted "routine" 4-minute CACh, done 10 days after the last ECACh, produced a similar degree of obstruction as ECACh, thereby indicating that a brief procedure will suffice for clinical purposes. By identifying a reproducible reaction plateau, CACh offers a new parameter for outlining the individual dimensions of airway hyperreactivity in children with asthma.