Inhibition by sodium cromoglycate of bronchoconstriction stimulated by respiratory heat loss: comparison of pressurised aerosol and powder.

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Abstract
Protective effect was examined of 3 doses (2, 10 and 20 mg) of sodium cromoglycate inhaled from a pressurized metered dose inhaler on the response to isocapnic hyperventilation of cold dry air in 10 asthmatic subjects. This was compared with the effect of cromoglycate powder (20 mg) inhaled from a Spincap and with placebo given on 2 occasions. The medications were inhaled on separate days, in random order and with use of a double-blind double-dummy technique, 20 min before isocapnic hyperventilation of 2-fold increasing volumes of air (-15.degree. C, 0% humidity) to produce a 20% fall in the post-treatment FEV1 [1-s forced expiratory volume]. The response was expressed as the provocative dose of respirtory heat loss required to cause a fall in FEV1 of 15% (PD15, kcal/min). Mean baseline spirometric indices exceeded 85% of predicted normal values on each test day; both placebo treatments reduced the baseline FEV1 by comparison with all active treatments (P < 0.0001). Comparison of the PD15 on the 2 placebo days confirmed excellent reproducibility. All doses of cromoglycate shifted the respiratory heat loss dose-response cure to the right of the placebo curve; PD15 after all active treatments exceeded PD15 after placebo (P < 0.0001). There was no cromoglycate dose-response relationship between the 3 doses of aerosol (P > 0.05), or between any dose of aerosol and powder (P > 0.05). Cromoglycate aerosol inhaled from a pressurized inhaler in a dose of 2 mg gives the same magnitude of protection against bronchoconstriction stimulated by airway cooling as 20 mg of pressurized aerosol or powder from a Spincap.