Relationship between bronchial airway responsiveness and clinical severity of asthma.

The minimum medication required to control symptoms was individually established in a systematic manner in 10 asthmatics. A scoring system for the severity of asthma was designed using the indices of initial airway calibre (a reflection of the degree of airway obstruction) and the minimum medication requirement; all the subjects were so scored. Bronchial airway responsiveness to histamine, methacholine and isocapnic hyperventilation of cold air was then measured in these subjects. The relationship between the level of bronchial responsiveness and the asthma severity score was examined. The mean airway responsiveness to histamine or methacholine for the subjects who required a combination of drugs was not significantly greater than that for those who required single medication intermittently or daily, while the airway responsiveness to cold air was significantly different between the subjects in the two treatment subgroups. Similarly, there was no correlation between the asthma severity score and airway responsiveness to methacholine and histamine (r = -0.38 and -0.48; P greater than 0.1) while a significant correlation was found with responsiveness to cold air (r = 0.72; P less than 0.02). The results suggest that there is a qualitative difference between the bronchoconstriction induced in asthmatic subjects by pharmacological constrictor substances and natural physical stimuli such as cold air.