Nocturnal asthma is defined by a drop in forced expiratory volume in 1 second (FEV1) of at least 15% between bedtime and awakening in patients with clinical and physiologic evidence of asthma.^[1] The pathophysiology of nocturnal asthma is closely associated with the chronobiology and the science of biologic processes that have time-related rhythms. Hence, understanding the circadian rhythm is important to interpret the changes in pulmonary function that occurs in sleeping asthmatics. A large population based study reported dyspneic episodes without therapy in asthmatics occurred between 10 P.M. and 7 A.M.^[2] Another population based survey that assessed 7729 patients, reported approximate 74% patients woke-up at least once a week with symptoms, 64% woke-up three times per week, and 39% patients woke-up every night with symptoms.^[3]

Nocturnal worsening of asthma is very common clinical finding in asthmatics affecting approximately 75% of asthmatics who awaken at least once per week because of symptoms, and approximately 40% experience nocturnal symptoms on a nightly basis.^[1][4]