ABSTRACT
Sleep is a reversible behavioral state of perceptual disengagement from the environment. The general depression of respiration, circulation, and other vital activity during this period has long been recognized. However, sleep is not a homogeneous phenomenon but is, rather, a physiologically heterogeneous condition characterized by frequent transient alterations in the state of consciousness. It can be subdivided into two fundamentally distinct neurophysiological states based on behavioral and electrographic characteristics: non-rapid-eye-movement (NREM), or quiet sleep, and rapid-eye-movement (REM), or active sleep (Carskadon and Dement, 1989). The effects of NREM and REM sleep on physiological processes are very different. In NREM sleep, mental activity is minimal or absent and respiration is controlled mainly by chemical-metabolic factors. In contrast, REM sleep is characterized by central nervous system activation associated with a variety of phasic events, which seem to be under behavioral influence. Similarly, respiration during REM sleep, especially phasic REM sleep, is largely independent of chemical-metabolic control but is influenced more predominantly by non-metabolicbehavioral factors (Phillipson and Bowes, 1986; Douglas, 1989).
