The intractable asthmatic children were compared with mild or moderate cases in the bronchial hypersensitivity to Ach. The 17 cases of the intractable group and the 29 cases of the control group inhalated Ach solution of 250, 500 and 750μg/ml concentration by Porta-Bird. When the decrease of FEV_1 became to 15% or more, or wheezing occurred, it was considered positive. The 4 healthy children inhalated Ach solution of concentration starting from 1000 μg/ml in a serial doubling manner until they could not inhalate any more because of the irritation of their throats. The 12 cases of the intractable group (71%) were positive on 250 μg/ml concentration in contrast with the 8 cases of the control group (28%). The average decrease of FEV_1 on 250 μg/ml concentration was 19.2±14.9% in the intractable group and 10.0±5.4% in the control group. On the other hand, the 2 of the 7 mild cases, having no wheezing during the last one year or more, were positive on 250 μg/ml. In the healthy children, one was positive on 800 μg/ml and others above 8000 μg/ml. When 20 mg of disodium cromoglycate, 1 capsule of Intal, was inhalated 5 minutes before Ach inhalation test, the fall of FEV_1, by Ach much decreased in both groups. In general, the intractable cases had more increased bronchial hypersensitivity than control cases. But there were a few cases having much increased bronchial hypersensitivity, though clinically very mild.
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