Nocturnal asthma: Mechanisms and treatment

Abstract

Recently, however, both our understanding and analysis of circadian biological rhythms have improved, and the evidence now suggests that they may underlie nocturnal asthma. A small but detectable diurnal variation in bronchomotor tone is found in normal people: the diurnal rhythm in peak expiratory flow has a mean amplitude of 8%. Asthmatics have a similar circadian pattern, but with an amplitude of 50%, implying that nocturnal asthma represents an exaggeration of the normal rhythm in bronchial tone. Asthmatic airways are hyperreactive to many constrictor stimuli, and nocturnal asthma is probably simply a manifestation of bronchial hyperreactivity. Indeed, there is a correlation between the degree of bronchial hyperresponsiveness to inhaled histamine and the amplitude of the diurnal variation in peak flow. So nocturnal asthma seems to be due to the factors responsible for the diurnal change in bronchomotor tone in normal people, with the changes in tone exaggerated because of bronchial hyperreactivity.