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Physiology of sleep |
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Sleep as defined by Hartmann (1973), cited by Turpin (1986) “is a regular, recurrent, easily reversible state of the organism, characterized by relative quiescence and by a great increase in threshold response to external stimuli.” Research undertaken by Barrie-Shevlin (1987) has shown that nurses fail to appreciate the need for sleep, let alone understand the stages of sleep and specific cycles. She cites Morgan and White (1983) in their study of Intensive Care nurses awareness of the need for sleep. They found that although nurses were aware of the importance of sleep, they did not always differentiate between essential and non-essential nursing tasks; so unnecessarily disturbed patients sleep. The aim of this literature review was to look at the physiology of sleep and to reinforce the importance of sleep and rest for the critically ill patient. STAGES AND CONTROL OF SLEEP. A means of identifying the different stages of sleep was discovered by Berger in the 1920’s,as cited by Finlay (1991). ... These recordings indicated various levels of electrical activity occurring in the brain; and so indicating differing stages of sleep. ... This information then makes it possible to clearly identify the dirrerent stages that occur during sleep (McGonigal 1986). McGonigal (1986) cites Webb (1975), Sanford (1979) and Hayter (1980) in their description of sleep stages. They all identify two types of sleep, Orthodox or non-rapid eye movement sleep (non-REM) and Paradoxical or rapid eye movement sleep (REM). ... This is the shallowest stage of sleep and the sleeper is still aware of the surroundings, this stage lasts only a few minutes. ... Lasts 10-20 minutes and is the deepest stage of sleep, it is difficult to wake the sleeper during this stage. This part of sleep relates to most peoples conception of what sleep is and is the period when most muscle relaxation occurs. Dreaming that occurs during non-REM sleep is a realistic thought like process, but is rarely remembered. The second type of sleep is REM sleep and has two stages to it. ... REM sleep is characterized by the appearance of low voltage electrical activity, very similar to the electrical activity recorded during wakefulness. Any dreaming that occurs in REM sleep is usually dramatic and emotionally charged, it is frequently recalled on waking (McGonigal 1986). All these stages of sleep merge into one another and form cycles of sleep. Daly (1989) states that an entire sleep cycle takes about 90 minutes and on average an individual passes through four or five cycles a night, if undisturbed. Uninterrupted completion of a whole cycle is thought to be essential, if sleep is to be beneficial. If woken partway through a cycle the sleeper then has to return to stage 1 non-REM sleep, and may therefore miss out on the other stages of sleep. Finlay (1991) states that during sleep stage 4 gradually decreases and REM sleep increases, with each sleep cycle that occurs. Stage 1 sleep only occurs during the first and last cycles, it is the emergent stage. One of the most crucial factors in the sleep wake profile is the internal “body clock” or circadian rhythm, which is independent of external factors. Halberg (1953) cited by Webster and Thompson (1986) introduced the term circadian to describe the approximate 24-hour cycle that many bodily functions follow; including sleep. ... Finlay (1991) indicates that in studies done on adults, the relationship between circadian rhythms and the sleep wake profile has been identified. ... Turpin (1986) supports the “body clock” theory he states that sleep is affected by an area in the hypothalamus that closely follows other circadian cycles, such as renal function and temperature control. ... basal metabolic rate, heart rate and body temperature Webster and Thompson (1986) suggest that different neurological systems are responsible for different stages of sleep, and that the control of sleep is dependent on the inter-relationship between two antagonist cerebral mechanisms - one active and one passive. |
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Title: Physiology of sleep
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