Circadian rhythms of respiratory functions in asthmatics

35 subjects underwent pulmonary function tests, plasma cortisol and urinary catecholamine measurements at 4-hour intervals, during a period of 24 h. In healthy subjects a circadian variation was not demonstrated. In asthmatic subjects circadian variation of a large number of ventilatory variables and a normal circadian pattern for plasma cortisol were demonstrated. Asthmatic patients were divided into two groups: patients with intrinsic asthma and patients with extrinsic asthma. The former showed the most impressive circadian pattern; the most severe bronchospasm occurred between 12.00 and 00.00 h; patients with extrinsic asthma, older than 20 years became worse around 03.00 h. During this period their urinary catecholamines reached the lowest values. The younger patients with extrinsic asthma presented the highest TGV values at 12.50 h. From the clinical viewpoint, it is emphasized that chronobiologic criteria could be utilized for the chronotherapeutic management of asthmatics.