Relevance of Symptom Variability for Control and Management of COPD

Abstract

Physiological and cellular functions operate in a 24-hour cyclical pattern orchestrated by an endogenous process known as the circadian rhythm. Airway calibre exhibits a circadian variation with maximum values occurring around noon and minimum values in the early morning. The mechanisms behind the daily variation are complex, but it has been speculated that autonomic input to airway tissues via the vagal nerve plays an essential role. In chronic obstructive pulmonary disease (COPD), there is important daily variation of respiratory symptoms, which are present in approximately half of the patients. This time-dependent variability has important consequences since it has an impact on daily life physical activity, sleep quality, severity of symptoms, exacerbations or health-related quality of life, which in turn represents a component of instability within a period previously considered as relatively calm. This article reviews the symptomatic variability in COPD, its pathophysiological basis, characteristics, determinants, potential consequences and therapeutic implications.