Circadian rhythm in airway responsiveness and airway tone in patients with mild asthma.

To determine the characteristics and reproducibility of circadian rhythms of airway responsiveness to histamine and methacholine and their relationship to airway tone in patients with mild asthma, we studied nine subjects with complaints of nighttime awakening due to dyspnea and/or cough at least once a week. Their mean age was 31.4 yr (range 17-65) and their mean daytime FEV1 was 99 +/- 14 (SD) % predicted. Forced expiratory volume in 1 s (FEV1) and the provocative concentrations of histamine and methacholine necessary to decrease FEV1 by 20% (PC20FEV1) were determined every 4 h for 13 consecutive measurements. Three subjects were measured with histamine, three with methacholine, and three with both histamine and methacholine. Data were evaluated on an individual basis. PC20FEV1 to histamine and methacholine showed significant and reproducible circadian variations in all cases (P less than 0.01 each) with a mean amplitude of 1.00 +/- 0.17 (SD) doubling concentrations for histamine and 1.35 +/- 0.29 doubling concentrations for methacholine. The amplitude of PC20FEV1 was significantly larger (P less than 0.05) and the time of maximum responsiveness was significantly earlier (P less than 0.05) with methacholine compared with histamine. FEV1 showed significant (P less than 0.05) circadian variations in three of nine subjects, and peak expiratory flow rate showed variations in two subjects. Correlation between the variations of FEV1 and PC20FEV1 was significant (P less than 0.05) in 5 of 12 cases.(ABSTRACT TRUNCATED AT 250 WORDS)