(2) Inspiratory Muscle Hyperreactivity in Children with Severe Asthma

Intercostal EMG's (EMGic) and diaphragmatic EMG's (EMGdi) were studied to evaluate the role of the inspiratory muscles in compensation for an increased load during provocation tests with methacholine. The EMG's were obtained with surface electrodes. Methacholine provocation tests were performed using an Astograph which demonstrated the dose response curve to respiratory resistance (Rrs) on an X‐Y recorder. The moving averages were analyzed in terms of the rates of rise (Xp/Ti) and peak activities (Xp). Experiments were performed on 15 asthmatics, aged 11 to 17 yrs, (6 mild and 9 severe asthmatics) and three normal subjects, aged 8 to 13 yrs. Pulmonary function values before provocation tests, except for mid‐maximal expiratory flow (MMEF), showed no significant differences among these three groups. Changes in Xp and Xp/Ti were measured at the degree of 1.5 and 2 times the initial respiratory resistance level. In severe asthmatics, the changes in Xp and Xp/Ti were significantly larger than those of mild asthmatics, especially in intercostal Xp/Ti. From our results, the severe asthmatics had respiratory muscle hyper‐reactivity compared with mild asthmatics, especially in the intercostal muscles.