Night, darkness, sleep, and cardiovascular activity.

We humans tend to spend a significant fraction of the night asleep in the dark and to stay awake with daylight. However, the widespread availability of electrical power is progressively imparting 24/7 activity schedules to our modern societies, in which artificial ambient light and illuminated screens of electronic devices allow people to stay awake at night for work or leisure, postponing sleep. Sleep disorders such as insomnia and sleep-disordered breathing may reduce the quantity and quality of nocturnal sleep and entail excessive daytime sleepiness as a consequence. Not only these environmental and behavioral factors but also a range of genetic, epigenetic, and age-dependent factors may cause the body to be regulated out of phase with the environment, mimicking in many respect conditions of jet lag associated with long-range flights. This chapter will discuss the effects of night/day, darkness/light, and sleep/wakefulness on cardiovascular activity considering firstly each factor on its own and secondly the interactions among the different factors. The chapter will focus on the control of arterial blood pressure and heart rate in human subjects. The chapter will also touch upon the hemodynamic consequences of the control of vascular resistance and blood volume, as well as upon the bidirectional translation between research on human subjects and model organisms such as mice, which are arguably the mammals of choice for mechanistic studies of functional genomics