Nocturnal asthma and urinary adrenaline and noradrenaline excretion.

, , 677-683. Urinary adrenaline and noradrenaline excretion, heart rate, and peak expiratory flow rate have been measured every two hours for 24 hours in seven asthmatic patients suffering from nocturnal or early morning exacerbations of dyspnoea. The excretions of these catecholamines were normal or slightly raised, this being consistent with a normal response to asthma or the conditions of the test. The expected physiological fall in catecholamine excretion occurred at night. In every patient the peak expiratory flow rate fell to its lowest values during the period of lowest catecholamine excretion, and the mean two-hourly peak expiratory flow rate for all seven patients was significantly related to the sum of the mean adrenaline and noradrenaline excretion in each preceding two-hour period (p<0·05). Individually, in three patients the relationship between peak expiratory flow rate and adrenaline and noradrenaline excretion during the evening and night was so close as to be consistent with the hypothesis that changes in sympathetic tone mediated the changes in asthma. In a further three patients the relationship was present but less clear, and in one the changes in peak flow rate and catecholamine excretion were dissociated. Studies of mean heart rate and sinus arrhythmia gap suggested that an increase in vagal tone at night might have mediated the early morning asthma in the patient in whom changes in catecholamine excretion were dissociated from change in peak flow rate. These findings would be consistent with the view that the physiological reduction in sympathetic tone at night mediates the nocturnal and early morning exacerbation of dyspnoea in some asthmatics, although other mechanisms such as alterations in vagal tone must be important in others. Confirmation of a causal relationship requires further study.