An Investigation of the Effects of Heat and Water Exchange in the Recovery Period after Exercise in Children with Asthma

It has been reported that asthma provoked by breathing subfreezing air during exercise is enhanced when air at btps is inhaled in the recovery period (1). It was concluded that the rate of airway rewarming is an important event in asthma provoked by exercise. It is also possible, however, that the enhanced response was due to hypo-osmolarity caused by condensation of water from inspired air at btps on the cooled mucosa. We examined, in a group of boys with asthma, the response to rapid rewarming of the airways after exercise, with and without the potential for condensation. On two test days, two exercise tests were performed 4 h apart on a cycle ergometer. On Day 1 (n = 17), the inspired air during exercise was −5° C, dry. During recovery, the air was either −5° C, dry or 50° C, 23 mg H1O/L. On Day 2 (n = 11), the inspired air during exercise was −15° C, dry, and during recovery was either −15° C, dry or at btps. We did not find enhancement of the response with either condition designed to cause rapid airway rewarming. On Day 1 the mean (± 1 SD) percent fall in FEV1 was 23 ± 22 (−5° C, dry) and 24 ± 21 (50° C, 23 mg H2O/L) (r = 0.92), and on Day 2 it was 19 ± 17 (−15° C, dry) and 18 ± 17 (btps) (r = 0.96). To test their response to airway hypo-osmolarity, the boys (n = 15) were tested on a third day with ultrasonically nebulized water. As a group, they were relatively unresponsive. The mean maximal percent fall in FEV1 after 13.9 (± 3.6) ml had been delivered was only 11.7% (± 6.6%). We could not show enhancement of the response to exercise with rapid airway rewarming. Therefore, we were not able to prove or disprove the hypothesis that condensation of water caused the enhanced response observed by McFadden and colleagues (1). Our observations, however, are not consistent with the hypothesis that rapid airway rewarming causes exercise-induced asthma.