Page 203 - Cardiac Nursing

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C HAPTER 8 / Sleep 179
MEAN SLEEP LATENCY (min) 20
15
10
0 5
0930 1330 1730 2130 0130 0530 0930
TIME
■ Figure 8-3 Mean sleep latency in minutes in young adults (open
circles) and old adults (solid circles) at different times of day. The
shaded area represents the night-time sleep period. A biphasic rhythm
exists with maximal sleepiness in the mid-afternoon and early morn-
ing, as indicated by shorter latencies. (From Richardson, G. S.,
Carskadon, M. A., Orav, E. F., et al. [1982]. Circadian variation of
sleep tendency in elderly and young adult subjects. Sleep, 5[Suppl. 2],
S87.)
is typified by abnormal movements, behaviors, and dream enact-
ment during REM sleep. Phasic REM sleep occurs intermittently
and is characterized by bursts of REMs (for which the stage is
named), muscle twitches in the face and distal extremities (potent
motor excitation briefly overrides the paralysis), and fluctuations ■ Figure 8-4 Normal sleep cycles in children, young adults, and
in blood pressure, heart rate, and breathing. 18 the elderly. Rapid-eye-movement (REM) sleep (darkened area) occurs
Approximately 80% of people awakened from REM sleep and cyclically throughout the night at intervals of approximately 90 minutes
40% awakened from NREM sleep report having dreams. In in all age groups and shows little variation in the different age groups,
NREM sleep, the mental activity tends to have a dull, sketchy whereas stage 4 non-REM (NREM) sleep decreases with age. In ad-
quality without much basis in reality. In contrast, dreams recalled dition, the elderly have frequent awakenings and a marked increase in
from REM sleep are usually vivid, well-formed, story-like narra- total wake time. (From Kales, A., & Kales, J. D. [1974]. Sleep disor-
tives. Dreams include more visual imagery and emotional tone as der. New England Journal of Medicine, 290, 488.)
the night progresses in relation to longer REM periods and greater
4
intensity of phasic events. Penile and clitoral erections also often
occur during REM sleep.
Adults typically change their body position 40 to 50 times dur-
ing a normal sleep period; the characteristics and number of
Sleep Cycles movements that occur are relatively stable personal traits. 19–21
Major body shifts often occur at changes from SWS to lighter
Most people have their major sleep period at night, organized in NREM stages or from REM to NREM sleep. A sudden muscle
a rhythmic sequence of sleep stages (Fig. 8-4). After a short period contraction involving all or part of the body (hypnic jerk, hypnic
of relaxed wakefulness, a young adult enters stage 1 sleep, followed myoclonus, or sleep start) often accompanied by intense visual
by a descent into stage 2 for 10 to 25 minutes and approximately imagery occasionally occurs at sleep onset and is normal; however,
20 to 40 minutes of SWS. The sleeper then goes through stage 2 the frequency of the events may increase with stress or irregular
and has a brief REM period approximately 90 minutes after sleep sleep schedules. 4,22
onset (the period from sleep onset to the first REM period is re-
ferred to as REM latency). The cycle begins again and repeats an-
other four to six times during the night. Slow-wave sleep occupies The Function of Sleep
less of the second cycle and may then disappear, whereas REM pe-
riods lengthen across the night. Therefore, most SWS occurs in The function of sleep remains a topic surrounded by controversy.
the first third of the night, and most REM sleep occurs in the last Some have postulated that it is important for mental and physical
third. If an awakening occurs, the sleep cycle typically starts again restoration 23,24 and energy conservation. 25,26 Others propose that
with stage 1 sleep. Frequent disruptions of sleep prevent the nor- the primary function of sleep is the maintenance of synaptic and
mal progression into SWS and REM sleep and increase stages 1 neuronal network function, information processing, and synaptic
and 2 sleep. 4,15 plasticity. 27–31 Sleep deprivation studies have shown that total and