Absence of refractoriness in asthmatic subjects after exercise with warm, humid inspirate

Twelve asthmatic adults each completed two six minute treadmill runs separated by an interval of 20 minutes. Running speed was constant for each subject, and inspired air temperature averaged 5.5 degrees C (SD 1.5 degree) for both tests. Total minute ventilation and total respiratory heat loss showed no significant difference between the two runs. Forced expiratory volume in one second (FEV1) was measured before exercise and at five minute intervals throughout the recovery periods, during which subjects breathed room air at an average temperature of 17.8 degrees C (1.8 degree). Reduction in FEV1 from pre-exercise readings averaged 39.3% (13.3%) for the first run and 11.5% (7.3%) for the second. On another day the subjects underwent an identical procedure except that the first exercise period was performed with the saturated inspirate at 37.3 degrees C (1.7 degree). This run produced a mean FEV1 reduction of only 3.1% (7.3%). The ensuing run, during which the inspiratory temperature averaged 6.0 degrees C (2.0 degrees), led to a mean fall in FEV1 of 37.3% (17.3%). This was not significantly different from the value recorded for the first of the paired runs with cool air. We therefore have been unable to confirm that exercise with warm humid inspirate may induce refractoriness to exercise induced asthma. Our data are compatible with the theory that refractoriness may be due to depletion of mediators during an initial exercise induced asthma attack.