Reversible airway obstruction: neurohumoral mechanisms and treatment. Lecture on nocturnal asthma.

Nocturnal wheeze has been known for at least 300 years, but only recently widely recognised. Wakening between 3 and 4 a.m. with wheeze may be associated with a 'morning dip' in peak expiratory flow rate (PEFR), worse in REM sleep, and with a circadian rhythm. Earlier suggestions that plasma histamine rose with nocturnal bronchoconstriction cannot be confirmed, but circulating adrenaline may be reduced in asthmatics at night. Hypoxia at night is common in asthmatics, associated with hypoventilation in REM sleep. Increasing frequency of nocturnal wheeze may herald acute severe asthma. Beta 2 agonists inhaled on retiral do not last to prevent the 'morning dip' in PEFR, but slow-release theophyllines can prevent this, and also relieve symptoms. However, sleep is still disturbed (by EEG criteria), as is nocturnal hypoxaemia. Nocturnal wheeze and/or 'morning dip' in PEFR occur in both atopic and non-atopic asthmatics, and the mechanism of nocturnal wheeze remains to be determined. Recognition of this common symptom remains a major indication for oral slow-release theophyllines.