Exercise-Induced Asthma

Exercise maintained for approximately eight minutes results in a fall in F.E.V.1 a rise in airway resistance, and impaired gas distribution in asthmatic subjects. These effects are usually maximal within 15 minutes after cessation of exercise and recovery takes place over the next 30 minutes. Measurement of airway resistance before and after exercise in normal subjects suggests that the same mechanism is operating in them. Hyperventilation stimulated by the inhalation of carbon dioxide has failed to produce a similar effect. Chlorpromazine, atropine, mepyramine maleate, and hydrocortisone administered before exercise have failed to block the effect but adrenaline has succeeded. It has been possible in a few subjects to lessen the effect of exercise by repeated exercise on the same day and we interpret this as pointing towards the depletion of a bronchoconstrictor substance released in the earlier periods. The possible substances are discussed.