Bronchoconstriction Stimulated by Airway Cooling

We compared the effect of inhaled terbutaline sulphate (1,000 micrograms), cromolyn sodium (20 mg), terbutaline plus cromolyn, and placebo on the response to respiratory heat loss (RHL) in 10 asthmatics in whom terbutaline alone did not completely inhibit the response to RHL. The medications were taken double-blind in random order 20 min before voluntary isocapnic hyperventilation of subfreezing air (-14 degrees C, 0% humidity) in twofold-increasing amounts. The response was expressed as the provocative dose of RHL to cause a 10 and 20% fall in forced expiratory volume in one second (FEV1). When compared with placebo, terbutaline produced bronchodilation and inhibition of the response to RHL. The degree of bronchodilation was small (mean delta FEV1, 3.9%) and did not correlate with the degree of protection. Cromolyn produced no bronchodilation and similar inhibition. The effect of terbutaline and cromolyn together was additive. We conclude that when bronchoconstriction stimulated by airway cooling is not prevented by a beta agonist or cromolyn given individually, that it will be more effectively inhibited by the 2 drugs given in combination.