Refractory period after exercise-induced asthma unexplained by respiratory heat loss.
Fifteen asthmatic children and young adults each exercised for 6 min by cycling on a cycle ergometer while breathing either cold (4.1 degrees C +/- 0.5 SEM) and dry (2.05 mg/L +/- 0.05) air or warm (37.2 degrees C +/- 0.3) fully saturated air. Each subject performed 4 tests arranged in pairs. Test pair A consisted of cold dry exercise followed by another cold dry exercise and test pair B consisted of a warm humid exercise followed by a cold dry exercise. Ventilation, heart rate, and gas exchange were closely matched in all 4 tests in each subject with a mean oxygen consumption of 34.8 +/- 0.8 ml/min/kg. In test pair A, all subjects were rendered refractory by the first cold dry exercise as manifested by a significant attenuation of their exercise-induced asthma (EIA) after the second cold dry test (per cent decrease in FEV1, delta FEV1 = 16 +/- 4 compared with 38 +/- 4). In 3 subjects, the warm humid exercise did not cause EIA and did not render them refractory to the second cold dry exercise. The 12 remaining subjects exhibited a refractory period similar to that shown in test pair A. They did not develop EIA after the warm humid test (delta FEV1 = 1 +/- 2), but after the subsequent cold dry exercise the per cent decrease in FEV1 was 19 +/- 3, similar to that in the second of the 2 cold dry exercise tests. These experiments suggest that in the majority of subjects exercise per se appears to be the cause for refractoriness and not airway cooling or bronchoconstriction.
D000293:Adolescent; D000328:Adult; D001249:Asthma / Q000503:physiopathology*; D001250:Asthma, Exercise-Induced / Q000503:physiopathology*; D001833:Body Temperature Regulation; D002648:Child; D005260:Female; D005541:Forced Expiratory Volume; D006636:Histamine Release; D006801:Humans; D008297:Male; D012119:Respiration; D013997:Time Factors; D014630:Vagus Nerve / Q000503:physiopathology