[Chronobiology of the bronchial system]

Control of breathing, bronchomotor tone and lung function are inferior to circadian rhythms, which can already be demonstrated at healthy subjects. They get relevant especially at patients with obstructive airway disease and sleep disturbances. Particularly in the early morning hours flow resistance in the airways and in the nose rises. Several different mechanisms are suspected to be responsible: Allergen exposure in bed, supine position, interruption of the bronchodilator therapy, gastro-oesophageal reflux, tenseness of the airways and secretory accumulation. Connected to nocturnal asthma might also be an increased airway responsiveness. Several factors contribute to nocturnal asthma, but they don't constitute a general concept for the explanation of nightly exacerbations. Many hormonal neural cellular and humoral factors show diurnal fluctuations which favour a constrictive bronchial response in the night. Diurnal or ultradian changes in O2 and CO2 sensitivity only play a minor role. However, we have to realise alterations in the responses of the central neuronal control mechanisms of breathing within the respiratory cycle. Oscillations of arterial CO2 partial pressure or pH-values influence tidal volume and ventilation directly. Circadian changes of different vital functions cause minor alterations in airway responsiveness and airway resistance in normal subjects, however in patients with asthma they are enlarged in amplitude and become relevant especially in the night and early morning hours.