Circadian variation in allergen and nonspecific bronchial responsiveness in asthma

In a majority of patients, exacerbations of asthma occur more frequently du ring the night than day. Many hypotheses have been proposed to explain such Variation in asthma. The airways of asthmatic persons are characterized by an abnormal degree of inflammation and bronchial hyperresponsiveness to bo th nonspecific and specific challenges. Studies of both children and adults with asthma document marked circadian rhythmicity in the response of airwa ys to bronchial challenges with histamine, methacholine, acetylcholine, sal ine, and house dust mite. Taken together, the findings of these investigati ons indicate that the hyperreactivity of airways to these agents is more pr ofound and prolonged following evening and overnight tests compared to test s conducted in the midday and afternoon. The temporal pattern in bronchial response to the hyperventilation of cold dry air is different. The hyperres ponsiveness of airways to this challenge is greatest in the afternoon. The amplitude of the circadian rhythm in airway hyperreactivity seems to be cor related to the amplitude of the circadian rhythm of pulmonary function; the greater the day-night difference in bronchial reactivity is, the greater i s the day-night difference in flow rates.