Reduced hyperpnea-induced bronchospasm following repeated cold air challenge

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Abstract
This study assessed reduction in expiratory function in 12 asthmatic subjects both after 5 min of cold air provocation (CAP) with dry air conditioned to .apprx. 0.degree. C and after exercise (to 85% of predicted maximum heart rate) while breathing ambient room air (.apprx. 21.degree. C and 40% relative humidity). These assessments were done both before and after the following training protocol. Three 5-min periods of isocapnic cold air hyperpnea separated by 5-min rest periods were performed breathing 0.degree. to -10.degree. C air, for 36 sessions over 12 wk. As expected, pretraining expiratory function was significantly reduced (P < 0.001) after both CAP and exercise. The posttraining reduction in expiratory function after CAP and exercise, however, was significantly less pronounced (largest P < 0.05). These data support our hypothesis that repeated bouts of cold air challenge result in airway acclimatization to cold air and consequent decrease in exercise-induced bronchospasm. Acclimatization may result directly either by habituation of the airways or by vasodilation leading to increased bronchial blood flow and consequent reduced airway cooling. An unanticipated finding, though, is that repeated cold air challenge may also cause long-term inflammatory changes in the airways. A significant percentage of subjects experienced reduced base-line pulmonary function and overall exacerabation of asthma symptoms during the training period.