Chapter 028. Sleep Disorders (Part 13) pps

Chapter 028. Sleep Disorders
(Part 13)

Circadian Rhythm Sleep Disorders
A subset of patients presenting with either insomnia or hypersomnia may
have a disorder of sleep timing rather than sleep generation. Disorders of sleep
timing can be either organic (i.e., due to an intrinsic defect in the circadian
pacemaker or its input from entraining stimuli) or environmental (i.e., due to a
disruption of exposure to entraining stimuli from the environment). Regardless of
etiology, the symptoms reflect the influence of the underlying circadian
pacemaker on sleep-wake function. Thus, effective therapeutic approaches should
aim to entrain the oscillator at an appropriate phase.
Jet Lag Disorder
More than 60 million persons experience transmeridian air travel annually,
which is often associated with excessive daytime sleepiness, sleep onset insomnia,
and frequent arousals from sleep, particularly in the latter half of the night.
Gastrointestinal discomfort is common. The syndrome is transient, typically
lasting 2–14 d depending on the number of time zones crossed, the direction of
travel, and the traveler's age and phase-shifting capacity. Travelers who spend
more time outdoors reportedly adapt more quickly than those who remain in hotel
rooms, presumably due to bright (outdoor) light exposure. Avoidance of
antecedent sleep loss and obtaining nap sleep on the afternoon prior to overnight
travel greatly reduces the difficulty of extended wakefulness. Laboratory studies
suggest that sub-milligram doses of the pineal hormone melatonin can enhance
sleep efficiency, but only if taken when endogenous melatonin concentrations are
low (i.e., during biologic daytime), and that melatonin may induce phase shifts in
human rhythms. A large-scale clinical trial evaluating the safety and efficacy of
melatonin as a treatment for jet lag disorder and other circadian sleep disorders is
needed.
Shift-Work Disorder
More than 7 million workers in the United States regularly work at night,

either on a permanent or rotating schedule. In addition, each week millions more
elect to remain awake at night to meet deadlines, drive long distances, or
participate in recreational activities. This results in both sleep loss and
misalignment of the circadian rhythm with respect to the sleep-wake cycle.
Studies of regular night-shift workers indicate that the circadian timing
system usually fails to adapt successfully to such inverted schedules. This leads to
a misalignment between the desired work-rest schedule and the output of the
pacemaker and in disturbed daytime sleep in most individuals. Sleep deprivation,
increased length of time awake prior to work, and misalignment of circadian phase
produce decreased alertness and performance, increased reaction time, and
increased risk of performance lapses, thereby resulting in greater safety hazards
among night workers and other sleep-deprived individuals. Sleep disturbance
nearly doubles the risk of a fatal work accident. Additional problems include
higher rates of cancer and of cardiac, gastrointestinal, and reproductive disorders
in chronic night-shift workers.
Sleep onset is associated with marked attenuation in perception of both
auditory and visual stimuli and lapses of consciousness. The sleepy individual may
thus attempt to perform routine and familiar motor tasks during the transition state
between wakefulness and sleep (stage 1 sleep) in the absence of adequate
processing of sensory input from the environment. Motor vehicle operators are
especially vulnerable to sleep-related accidents since the sleep-deprived driver or
operator often fails to heed the warning signs of fatigue. Such attempts to override
the powerful biologic drive for sleep by the sheer force of will can yield a
catastrophic outcome when sleep processes intrude involuntarily upon the waking
brain. Such sleep-related attentional failures typically last only seconds but are
known on occasion to persist for longer durations. These frequent brief intrusions
of stage 1 sleep into behavioral wakefulness are a major component of the
impaired psychomotor performance seen with sleepiness. There is a significant
increase in the risk of sleep-related, fatal-to-the-driver highway crashes in the
early morning and late afternoon hours, coincident with bimodal peaks in the daily

rhythm of sleep tendency.
Medical housestaff constitute another group of workers at risk for accidents
and other adverse consequences of lack of sleep and misalignment of the circadian
rhythm. Recent research has demonstrated that the practice of scheduling interns
and residents to work shifts of 30 consecutive hours both doubles the risk of
attentional failures among intensive care unit interns working at night and
significantly increases the risk of serious medical errors in intensive care units.
Moreover, working for >24 h consecutively increases the risk of needlestick
injuries and more than doubles the risk of motor vehicle crashes on the commute
home. Some 20% of hospital interns report making a fatigue-related mistake that
injured a patient, and 5% admit making a mistake that results in the death of a
patient.
From 5–10% of individuals scheduled to work at night or in the early
morning hours have much greater than average difficulties remaining awake
during night work and sleeping during the day; these individuals are diagnosed
with chronic and severe shift-work disorder (SWD). Patients with this disorder
have a level of excessive sleepiness during night work and insomnia during day
sleep that the physician judges to be clinically significant; the condition is
associated with an increased risk of sleep-related accidents and with some of the
illnesses associated with night-shift work. Patients with chronic and severe SWD
are profoundly sleepy at night. In fact, their sleep latencies during night work
average just 2 min, comparable to mean sleep latency durations of patients with
narcolepsy or severe daytime sleep apnea.