Pathogenesis and pathophysiology of nocturnal asthma.

Nocturnal wheezing is a major component of asthma. This article reviews the many factors (allergen exposure, sleep, airway cooling, diminished clearance of mucous secretions) that have been identified as contributing to nocturnal asthma. Also discussed are recent data suggesting that diurnal variations in hormone concentrations and in autonomic nervous system control are possible mechanisms of nocturnal asthma. Decreased epinephrine secretion and increased vagal tone during sleep not only cause airway obstruction but may also enhance bronchial reactivity. These changes in the modulation of airway smooth muscle tone produce bronchial obstruction, which, in turn, accentuates ventilation-perfusion mismatch and increases hypoxia.