Physiological Risks During Sleep

Abstract

The concept of homeostasis [1] underlies the understanding of regulatory mechanisms in several physiological domains. Homeostasis of the variables directly affecting cellular survival is achieved by continuous functional adjustments meeting challenges arising in the internal and external environments. Such adjustments depend on the action of feedback mechanisms, whose properties in the open- or closed-loop modality of operation are now well understood. It is also clear that the regulation paradigms of effector activities vary across the behavioral states of wakefulness and sleep [9]. During wakefulness, cortically driven activity may occur according to the open-loop modality, but the resulting changes in physiological variables are always compensated for by closed-loop operations that preserve homeostasis. In its turn, synchronized sleep is characterized by closed-loop operation and the greater homeostatic efficiency of automatic functions. Open-loop operations (effector excitation or inhibition) prevail during desynchronized sleep, so that the impairment of homeostasis is the main feature of this stage of sleep. The temporal stability of such regulation paradigms, which are summarized in Table 1, underlies the existence and persistence of the different behavioral states [11].