EFFECT OF CIRCADIAN-RHYTHM ON BRONCHOMOTOR TONE AFTER DEEP INSPIRATION IN NORMAL AND IN ASTHMATIC SUBJECTS

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Abstract
Bronchomotor tone after deep inspiration and bronchial responsiveness to methacholine were studied at 4:00 A.M. and 4:00 P.M. in 14 normal and 13 asthmatic subjects. Bronchomotor tone was assessed with respiratory resistance (Rrs) measured by the forced oscillation method. Bronchial responsiveness to methacholine and baseline Rrs were higher at 4.00 A.M. than at 4:00 P.M. in both normal and asthmatic subjects (P < 0.01). The difference in methacholine threshold between 4:00 P.M. and 4:00 A.M. in asthmatics was similar to that in normal subjects. Immediately afte deep inspiration, Rrs decreased more at 4:00 A.M. than at 4:00 P.M. in normal subjects. In contrast, asthmatic subjects showed a significantly greater immediate increase in Rrs after deep inspiration at 4:00 A.M. than at 4:00 P.M. The bronchoconstrictive effect after deep inspiration is a distinguishing characteristic of asthmatics.