Diurnal variation in bronchial responsiveness in asthmatic children.

To establish the presence of a diurnal variation in bronchial responsiveness in asthmatic children, the increase of peak expiratory flow rate (PEFR) following sympathomimetic inhalation and the response to bronchial provocation with histamine and hyperventilation of cold dry air (HVCDA) were studied. Twenty-nine patients (20 boys, nine girls, aged 9.3 to 17.8 years) measured PEFR before and after sympathomimetic inhalation three times a day for four weeks. A further 15 patients (eight boys, seven girls, aged 6.9 to 18.0 years) underwent bronchial provocation testing every six hours for 24 hours. A diurnal variation in bronchodilator responsiveness was demonstrated in 55% of the first group. Mean amplitude was 60.8% of patients' mean increase in PEFR following bronchodilators. On grouped data, bronchodilation was greater in the morning than in the afternoon (p less than 0.0005) or in the evening (p less than 0.0005). A diurnal variation in the response to bronchial provocation was also found in the second group, but the timing of the rhythm depended on the stimulus used. On grouped data, airways were most sensitive to histamine at 0400 hours and most sensitive to HVCDA at 1600 hours. The diurnal variation demonstrated in bronchial responsiveness could not be attributed to changes in baseline airway caliber and was present, despite the patients' taking sufficient medication to control their asthmatic symptoms.