Changes in respiratory resistance (Rrs) upon methacholine inhalation in adult asthmatics were monitored by a new device"Astograph", which measured the Rrs by the forced oscillation method. 215 cases of adult asthma, 20 and 17 cases of acute and chronic bronchitis, 7 cases of allergic rhintitis and 24 cases of healthy adults were subjected to examination as to bronchial hyperresponsiveness. The method proved to be useful in the evaluation of bronchial hyperresponsiveness with respect to reproducibility, safety and convenience. The analysis of different parameters in an "Astogram"recorded by the"Astograph"gave some clues to understanding the mechanisms of bronchial hyper-responsiveness: 1. The values of control respiratory resistance (Rrs. cont), which were measured during the inhalation of the saline aerosol by subjects with the various diseases showed significant correlation with FEV_<1.0>% and % FEV_<1.0>, showing the state of airway obstruction. 2. The values of two important parameters, Dmin, which reflected bronchial sensitivity, and St for bronchial reactivity, showed no significant correlation within each disease group or among the healthy individuals. These results suggest that bronchial sensitivity and reactivity might be regulated by different physiologic mechanisms. 3. These two parameters (Dmin and St), migrated differently in the following way in accordance with the nature of the disease. a) In the case of bronchial asthma, both atopic and nonatopic, Dmin and St were higher than those parameters in the other disease groups examined. b) In allergic rhinitis, Dmin was nearly the same level as in normal individuals; however, the value of St was close to that of subjects with bronchial asthma. c)In the bronchitis group, the value of Dmin was lower than the of the control group, while St showed a higher value than that of the control group.
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