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180 PA R T I I / Physiologic and Pathologic Responses
partial sleep loss impair well being and functioning, with mood circadian processes via their influence on thermoregulatory and
being the most strongly affected, followed by cognitive and motor neuronal/neurohormonal systems. 45–47 Factors that either oppose
performance. 32–34 Most agree that although the exact function of or enhance these processes can have significant effects on the tim-
sleep remains to be discovered, it fulfils a vital need, one that is es- ing, duration, and structure of sleep as well as daytime alertness.
sential to human health and well being. 35
Sleep plays an important role in thermoregulatory 36–38 and Developmental Variations
immune processes. 39,40 Special areas in the hypothalamus and in Sleep Patterns
basal forebrain integrate temperature and sleep control through a
network of complex interactive processes. For example, an in- One of the most important factors affecting the pattern of sleep
crease in brain temperature before sleep onset increases sleep across the night is age (see Fig. 8-4). During the first years of life,
depth while deep sleep increases heat loss by stimulating vasodi- the transition from wake to sleep typically occurs through REM
latation and reduction of the metabolic rate. Peripheral signals sleep observed as active sleep in newborns when phasic muscle ac-
coming from skin thermosensors going to these brain regions can tivity and eye movements can be observed. This is in sharp con-
also have a significant effect on sleep/wake state. 37,41 In fact, va- trast to adults in whom sleep is normally entered through NREM
sodilatation of blood vessels in the feet in response to local sleep. The sleep cycle of a newborn occurs every 50 to 60 minutes
warmth was recently shown to be an independent predictor of compared to 90 minutes in the adult, and sleep is intermittently
sleep onset. 42,43 Many immune factors such as interleukin-1, dispersed across both the day and night. Gradually, over a period
interleukin-2, and tumor necrosis factor- have been shown to of 2 to 6 months, infants develop a consolidated nocturnal sleep
promote deep sleep, possibly because of the associated increased period once appropriate brain structures and process have devel-
heat production. 40 Thus, the interaction of sleep, thermoregula- oped.
tion, and immunological responses may explain why patients be- SWS is at its peak in young children and is much deeper than
come sleepy when having fevers and infections. Sleep deprivation that of adults. For example, it is not uncommon for a child’s
has also been associated with reduction in the activity of natural clothes to be changed and to be put to bed without awakening.
killer cells in response to a bacterial or viral load, suggesting a direct However, a subsequent decrease in SWS occurs across adoles-
link between sleep and immune function. 39,44 cence, a trend that continues to occur with age. REM sleep, as a
percentage of total sleep time, is relatively well maintained across
Regulation of Normal Sleep the entire life span. 4
With increasing age, particularly in men, sleep becomes lighter
According to the Two-Process Model of Sleep Regulation, 45 the and more fragmented (see Fig. 8-4). In contrast to young adults,
major mechanisms controlling sleep and waking across time are: older people usually spend more time in bed but less time asleep
(a) a homeostatic process determined by previous sleep and wak- (reduced sleep efficiency) and are more easily awakened from
ing; and (b) a circadian process that designates periods of high and sleep. The time needed to fall asleep (sleep latency) shows little
low sleep propensity. The homeostatic process reflects the physio- change with aging, but more night-time awakenings, brief
logical need for sleep, which builds across the day and dissipates arousals, and stage changes occur. 48 There is a striking reduction
throughout the night (Fig. 8-5). 10 A key indicator of this process in SWS and an increase in stage 1 sleep, with little change in the
4
is EEG slow wave activity, which is high during the beginning of percentages of stage 2 and REM sleep. Bedtime and wake-up
a sleep episode but decreases as the night progresses. The circadian time come earlier (circadian phase advance), daytime sleep ten-
process, a sinusoidal rhythm of approximately 24 hours, is con- dency may be increased, daytime napping is more common, and
trolled by a biologic oscillator (suprachiasmatic nucleus). This tolerance for changes in the sleep–wake schedule is reduced. Sleep
process regulated sleep propensity and its effects a least in the early apnea (discussed later) and periodic leg movements (involuntary
morning hours. The rhythm of core body temperature is a key repetitive jerks) are more common in older adults and can con-
indicator of the circadian process. The timing and duration of tribute to sleep disruption. 49–54 Other factors may include poor
sleep are determined by the combined action of homeostatic and sleep habits, a reduced activity level, psychological concerns, phys-
ical illness, and medications. 48 Not surprisingly, older people of-
ten are dissatisfied with their sleep, complain of taking longer to
fall asleep, and have more frequent night-time awakenings—all of
which result in an increased using of sleeping medications. 55,56
Insomnia has been associated with increased mortality in the eld-
erly. 57 However, it now appears that sleep duration, whether it be
S excessively short or long, may not be a mortality risk factor in this
population but rather a function of the measurement of sleep
close to the time of death and the number of concurrent medical
C C conditions. 58
W Wakkinng S Sleep
SLEEP PHYSIOLOGY
23 7 23 7
Time of Day
■ Figure 8-5 The two-process model of sleep regulation. Two pri- The physiological basis of nursing care has rested almost entirely
mary processes regulate sleep: a homeostatic process determined by on studies of responses during wakefulness. However, NREM
prior sleep and waking, and a circadian process that designates peri- sleep, REM sleep, and wakefulness are very different physiological
ods of high and low sleep propensity. states associated with state-dependent changes in the function of