Priority of peak circadian variation of bronchial responsiveness to the trough of circadian variation of bronchial caliber in asthmatic children.

To study the temporal relation between the peak of circadian variation of bronchial responsiveness and the trough of circadian variation of bronchial caliber, we performed seven inhalation challenges with histamine at 4-h intervals in six stable asthmatic children aged eight to ten years. Bronchial responsiveness was expressed as PC20. Coefficient of variation of baseline FEV1 within the study day was less than 7 percent in all. The trough of FEV1 variation by cosinor analysis ranged from 02.50 to 11.99 h (mean, 05.66). All had both significant (p less than 0.05) or marginally significant (0.05 less than p less than 0.1) cosinusoidal rhythm of PC20 and two or more doubling concentration differences between the highest and lowest PC20s. The trough of PC20 variation ranged from 16.32 to 02.87 h (mean, 22.30). There was a significant (p less than 0.05) difference between troughs of FEV1 and PC20 variations. We conclude that the peak of circadian variation of bronchial responsiveness precedes the trough of circadian variation of bronchial caliber in asthmatic children.