Effects of Atropine on the Potentiation of Exercise-Induced Bronchospasm by Cold Air,

The role of vagal afferent activity in the cold air potentiation of bronchial obstruction after exercise in asthma was assessed by exercising 9 asthmatic subjects who breathed air at ambient and sub-freezing temperatures both before and after cholinergic blockade. Lung volumes and maximal expiratory flow volume curves with air and with 80 helium - 20 oxygen were obtained before and 5 to 10 minutes after each exercise challenge. Isovolume comparisons of maximal expiratory flow rates with the two gases were used to assess relative contributions of large and small airways to flow limitation. Exercise under ambient conditions resulted in the expected airway obstruction and cold air exaggerated the response. The writers conclude that the potentiating effects of cold air are local rather than vagally mediated and suggest that the immediate stimulus is related to cooling of intrathoracic airways. Both the greater response and the greater small airway contribution suggest a deeper penetration of incompletely conditioned air when exercise is performed in the cold.