Nocturnal Asthma: Mechanisms and Chronotherapy

Abstract

Asthma is a chronic obstructive airways disease. The underlying abnormalities are excessive contraction of tracheobronchial smooth muscle and hypersecretion of mucus plus musosal edema in association with airways inflammation (Spector 1982). Historical accounts of the disease describe a worsening of symptoms overnight. Nonetheless, most clinicians question the time dependency of this disease or feel that nocturnal asthma is a special subtype of asthma. In the majority of untreated patients asthma worsens, or occurs only, overnight. The increase in cough, wheeze, and breathlessness at this time causes substantial problems for patients (Pfeiffer et al. 1989). A number of hypotheses have been proposed to explain why asthma is so common overnight. These include day-night variations in certain environmental factors such as barometric pressure relative humidity, and ambient temperature; proximity and concentration of various offending antigens; accumulative effects of psychological and physiological stresses during the day; and assumption of a supine posture at night. An alternate explanation for the time dependency of this disease stresses the role of endogenous circadian bio-periodicities in relationship to changes in the external environment during each 24 h (Barnes 1984 a; Smolensky et al. 1981, 1986 a). With regard to chronobiological considerations, successful management of patients entails not only the institution of environmental control methods, but also an understanding of the circadian features of the disease to achieve a chronotherapy of anti-asthma medications (Reinberg et al. 1988a,b; Smolensky et al. 1986b, 1987a).