Circadian Rhythm in Respiratory Medicine

Endogenous clocks determine almost all circadian rhythms in physiology. Circadian rhythms are patterns of physiology and behavior that follow a 24-hour cycle. They are autonomous and consist of self-sustained oscillations in biological processes driven or stimulated by environmental processes, the most important being light. Examples are, to name a few, sleep-wake cycle, learning, memory, daily variations in blood pressure, temperature, mood, heart rate, exercise capacity, ventilation, and coagulation, and it is now realized that the time at which our immune system is triggered (by infection, vaccination, surgery), appears to be critical to the way we respond to these insults. Also, circadian clocks give physiological systems the ability to anticipate daily changes. The complex network consists of a master pacemaker in the central nervous system and peripheral molecular clocks neurologically or hormonally connected and trained by the central node. These peripheral clocks govern a vast panel of cellular and molecular processes at virtually every level of regulation, maintaining the stability of the internal environment and anticipating disturbances. The objective of this work is to review the molecular biology of the system, to understand how it can be impacted, negatively or positively, and to review its dysfunction in respiratory diseases. It is also discussed how the understanding of circadian rhythms in respiratory medicine can have significance in the treatment optimization. At the end, some future recommendations for research on this topic are made.