What is sleep?
There are over 20 definitions of "sleep" in
several dictionaries. The first, a verb, seems most appropriate:
to take the rest afforded by a suspension of voluntary
bodily functions and the natural suspension, complete or partial, of
consciousness; cease being awake.
Physiologically, sleep is a complex process of restoration
and renewal for the body. Scientists still do not have a definitive explanation
for why humans have a need for sleep. We do know that sleep is not a passive
process or "switching off" of body functions; sleep is believed to be
important in many physiologic processes including the processing of experiences
and the consolidation of memories. It is also clear that sleep is essential,
not only for humans but for almost all animals.
The importance of sleep is underscored by the symptoms
experienced by those suffering from sleep problems. People suffering from sleep
disorders do not get adequate or restorative sleep, and sleep deprivation is
associated with a number of both physical and emotional disturbances. In
addition, sleep is influenced by the circadian rhythms (regular body changes in
mental and physical characteristics that occur in the course of about 24
hours). These are controlled by brain neurons that respond to light,
temperature and hormones and other signals and comprise the body's biological
clock. This clock helps regulate the "normal" awake and sleep cycles.
Disruption of these cycles can make people sleepy at times people want to be
awake. For example, travelers experience "jetlag"
when they cross time zones. When a New Yorker arrives in Paris at midnight
Paris time, his or her body continues to operate (their biological clock) on
New York time. It may take some time (about 1-3 days) to reset a person's
biologic clock, depending on how much it has been altered by the time change.
There is evidence that some aspects of sleep are under
genetic influence; a gene termed DEC2 is being investigated as causing people
that possess it to require only about 6 hours of sleep. Researchers have only
begun to examine the genetics involved in sleep.
What are the stages of sleep?
There are two general states of sleep: 1) rapid eye
movement (REM) sleep, and 2) non-rapid eye movement (NREM) sleep. NREM sleep is
further subdivided into stages (see below).
1. REM sleep (rapid-eye movement):REM sleep is unlike any
of the other stages of sleep. It was first described in 1953 when sleep
researchers noticed a unique pattern of brain waves (signals recorded on an EEG), a type of test that measures the electrical
impulses within the brain). These brain waves had a fast frequency and low
voltage, similar to the brain waves seen in the normal awake state. Other
characteristics of REM sleep include complete inactivity of the voluntary
muscles in the body, with the exception of the muscles that control eye
movements. Rapid eye movements are also observed during REM sleep. People who are
awakened during REM sleep often report that they were dreaming at the time.
About 20% to 25% of sleep time is REM sleep; in infants it can comprise about
40%.
2. NREM (non-rapid eye movement):NREM sleep has
traditionally been considered to be divided into 4 stages. However, new
guidelines from the American Academy of Sleep Medicine (AASM) published in 2007
have recharacterized NREM sleep as occurring in 3 stages, according to the
pattern of brain electrical activity:
· Stage N1 sleep, or the transition from wakefulness to deeper sleep. This
is the lightest stage of sleep, and people may not always perceive they are
asleep when in this stage.
· Stage N2 sleep is a true sleep state, and accounts for 40% to 50% of
sleep time.
· Stage N3 sleep has been called deep sleep, delta sleep, or slow wave
sleep. This stage accounts for about 20% of sleep in young adults.
Sleep typically occurs in cycles that range from 90 to 120
minutes in length, with 4-5 cycles occurring during each night's sleep. In the
first half of the night, there is a transition from wakefulness into stage N1
sleep, then to stages N2, and N3. Stages N2 and N3 then reappear, followed by
the first instance of REM sleep. Cycles of stage N2 and REM sleep alternate
with each other for the second half of the night.
Disruptions in the entire sleep cycle or in the individual
phases are believed to account for the various types of sleep disorders.
How much sleep does a person need?
Individuals vary greatly in their need for sleep; there
are no established criteria to determine exactly how much sleep a person needs.
Eight hours or more may be necessary for some people, while others may consider
this to be too much sleep.
The National Institutes of Health
(NIH) suggests that most average adults need about 7 to 9 hours of sleep each
night. Newborn by contrast, sleep from 16 to 18 hours a day. preschool typically sleep between 10 and 12 hours a day. Older, school going and teen need at least 9 hours of sleep a night.
Women in the pregnancy have been observed to need a few more hours' sleep than is
usual for them.
Does the amount of sleep we need change as we age?
Changes in the sleep cycle do occur with aging. Deep or
slow wave sleep (Stage N3) sleep declines as we age, while light sleep (Stage
N1) increases with age, so that older adults may spend less time in the more
restorative stages of sleep and more time in lighter sleep. Older people are
also more easily aroused from sleep. While some people believe that older
adults need less sleep as they get older, there is no scientific evidence that
older people need less sleep than younger adults.
What are signs and symptoms of sleep deprivation?
Feeling tired or drowsy at any time during the day is a
symptom of not having enough sleep. Being able to fall asleep within 5 minutes
of lying down in the evening also may be a sign a person may be suffering from
sleep deprivation. People who suffer from sleep deprivation often experience
so-called "microsleeps," which are short bursts of sleep in an
otherwise awake person.
Sleep-deprived people perform poorly
on tests such as driving simulators and tests of hand-eye coordination. Sleep
deprivation can also magnify the effects of alcohol, meaning that a
sleep-deprived person will be more susceptible to becoming impaired after
alcohol consumption than a well-rested person. Caffeine and
other stimulants cannot successfully overcome the drowsiness associated with
sleep deprivation.
What are and what causes sleep disorders?
Sleep disorders are disruptions of the sleep cycle or the
quality of sleep. About 40 million Americans are believed to suffer from
chronic sleep disorders, with millions more affected on an occasional basis.
Doctors have defined over 70 different types of sleep disorders, but the most
common sleep disorders are insomnia, sleep apnea, restless legs syndrome, and
narcolepsy.
· INSOMNIA is
the perception of poor-quality sleep, including the inability to fall asleep or
stay asleep. Because people differ in their need for sleep, there are no fixed
criteria that define insomnia. Insomnia is very common and occurs in 30% to 50%
of the general population. Approximately 10% of the population may suffer from
chronic (long-standing) insomnia.
· SLEEP APNEA is
another common sleep disorder characterized by a reduction or pause of
breathing (airflow) during sleep. Central sleep apnea (CSA) occurs when the
brain does not send the signal to the muscles to take a breath, and there is no
muscular effort to take a breath. Obstructive sleep apnea (OSA) occurs when the
brain sends the signal to the muscles and the muscles make an effort to take a
breath, but they are unsuccessful because the airway becomes obstructed and
prevents an adequate flow of air. Mixed sleep apnea occurs when there is both
central sleep apnea and obstructive sleep apnea.
· RESTLESS LEG SYNDROME, also known as nocturnal myoclonus, is a type of
sleep disorder characterized by uncomfortable sensations in the legs and an
uncontrollable desire to move the legs. These abnormal sensations usually occur
in the lower legs shortly after going to bed. During the early stages of sleep,
these episodes of leg movement often last up to an hour. The abnormal
sensations of RLS are quite variable. They have been described as a crawling,
creeping, pulling, drawing, tingling, pins and needles, or prickly discomfort.
They are not cramping in character.
·NARCOLEPSY is
a disease of the central nervous system that results uniformly in excessive
daytime sleepiness (EDS). Other primary symptoms of narcolepsy include the loss
of muscle tone (cataplexy), distorted perceptions (hypnagogic hallucinations),
and the inability to move or talk (SLEEP PARALYSIS).
Additional symptoms can include disturbed nocturnal sleep and automatic
behaviors (affected persons carry out certain actions without conscious
awareness). All of the symptoms of narcolepsy may be present in various
combinations and degrees of severity.
Other sleep disorders include: Periodic limb movement disorder, Hypersomnia, sleep walking, snoring, nightmares and shift work sleep disorder.
How are sleep problems diagnosed?
Doctors use a number of different tests to evaluate sleep
and determine whether a sleep disorder is present. A careful medical history
and physical examination are performed to help identify any medical conditions
that may be interfering with the person's sleep. The health care practitioner
will also ask about the use of prescription and non-prescription medications as
well as alcohol, tobacco, and caffeine use. Laboratory tests may also be used
to help diagnose any medical conditions that may cause sleep problems.
In some cases, specialized testing is recommended to help
determine whether or not a person may be suffering from a sleep disorder. Some
of the most common sleep tests include the following:
·
Polysomnography is often simply referred to as a "sleep study." In this test, doctors use electrodes
attached to the face and scalp to measure brain waves (EEG) and muscle tone during a night's sleep. Other body
functions such as airflow, breathing effort, blood oxygen levels, leg
movements, (ECG),
and body position may also be measured if needed. Sleep studies are most commonly
performed in specially designed labs in hospitals or clinics.
·
The multiple sleep latency test (MSLT) is designed to measure daytime sleepiness. The test
is based upon the fact that the sleepier an individual is, the faster he or she
will fall asleep. In this test, the patient is given four to five opportunities
to nap in a quiet, dark room, usually at two hour intervals during the day.
Body functions such as EEG and muscle tone are measured as in polysomnography.
The time period needed from wakefulness to sleep onset is measured to determine
the "sleep latency." This is repeated during each of the naps, and an
average time for sleep latency across all the naps is calculated. Usually a
sleep latency of 5 minutes or less is signifies severe daytime sleepiness.
·
Related to the MSLT is the
maintenance of wakefulness test (MWT),
which measures the individual's ability to stay awake when reclining in a
quiet, darkened room.
·
The Epworth sleepiness scale is a questionnaire that is given to patients, often as part
of an office visit to a health care practitioner. The test asks individuals to
rate how likely they would be to fall asleep in a number of situations (such as
a passenger in a car, sitting quietly after lunch, etc.).
How are sleep problems treated?
The treatment of sleep disorders depends upon the exact
disorder and the degree of severity of the symptoms. Both medical and
non-medical approaches are generally used in the treatment of sleep disorders.
In some cases, such as sleep apnea, surgical treatments may be considered.
Sleep hygiene
Non-medical treatment options are often referred to as
sleep hygiene. Sleep hygiene is the practice of behavioral habits that offer
the maximum potential for restorative and sound sleep. Good sleep hygiene
practices include:
·
Avoid caffeine, nicotine, and alcohol use before bedtime. Some studies have shown
that caffeine consumed early in the day can have an effect on the ability to
fall asleep at night.
·
Have and adhere to a regular bedtime
and waking schedule
·
Maintain a comfortable sleep
environment, including a comfortable temperature
·
Do not lye in bed awake, worrying
about not sleeping (or anything else negative). This produces anxiety that can actually make the problem worse.
·
Get regular daily exercise (it is recommended that individuals avoid exercise two
hours prior to bedtime)
Other therapies
Of course, many people with sleep
disorders will require treatment beyond sleep hygiene measures. Behavioral therapies are successful for many people who
suffer from insomnia. These therapies may consist of stimulus control measures,
such as using the bed for sleeping and sex only and not for other activities
such as reading or TV watching. Sleep restriction therapies are often used to help individuals
avoid staying in bed too long and actually over-sleeping after a night of
insomnia.
Sleep aids (prescription and OTC)
Medications can be of value in treating some types of sleep disorders.
However, since sedating medications typically have the potential for addiction
and abuse, their use must be carefully supervised by a health care
practitioner.
·
In sleep apnea and other sleep
disorders in which airway obstruction is a problem, topical nasal decongestants
may provide some relief. However, many clinicians warn people with sleep apnea
never to use sleeping pills or medications that are sedative as the person
could be prevented from waking enough to stimulate breathing, which could lead
to brain damage or sudden death.
OTC sleep medications are sometimes used for the short-term treatment of
insomnia. These include the sedating antihistamines . However, this is not a recommended use of
these or other similar drugs due to their many side effects and the possibility
of long-term drowsiness the following day.
Melatonin a chemical released from the brain which induces sleep, has been tried in
supplement form and promoted as a natural sleep remedy for treatment of
insomnia. But studies have shown that it has been generally ineffective in
treating common types of insomnia, except in specific situations in patients
with known low levels of melatonin.
Dental appliances and CPAP devices (continuous positive airway pressure; a
device worn over the face that holds the airway open by maintaining constant
air pressure) have been effective in the management of sleep-related breathing
disorders, including sleep apnea.
Are sleep problems and disease related?
Sleep problems occur in a number of different medical and
psychiatric conditions. For example, asthama or stroke are
conditions that tend to occur frequently during the night or early morning
hours. The relationship between sleep stages and certain types of seizures is complex and not completely understood, but certain
sleep stages tend to either exacerbate or prevent the spread of seizure
activity in the brain.
Sleep problems occur with chronic pain and
conditions in which pain is worse at night, because the pain may interfere with
sleep. Pain medications and other types of medications taken on a regular basis
for chronic conditions can also have an effect on an individual's sleep
pattern. Those suffering from cancer and brain injury are also commonly affected by sleep disturbances.
Psychiatric diseases such as depression are also associated with sleep
problems. This condition can be associated with both too much sleep and too
little sleep. In fact, sleep problems are associated with a majority of mental
disorders, and poor quality or insufficient sleep can worsen the symptoms of mental illness.
How can I get a good night's sleep?
Practicing good sleep hygiene (see above), including
maintenance of a regular bedtime and awakening schedule, is the best way to
ensure restful and restorative sleep. Avoidance of caffeine, alcohol, nicotine,
and strenuous exercise in the hours prior to bedtime can also help improve the
quality of your sleep. Many people report that they lie awake at night worrying
about problems or situations they will face during the coming day. In this
case, it can be helpful to write a to-do list or a list of items to act upon
the following day prior to bedtime, giving yourself permission to "let
go" of these items during the night.
If you are concerned about the quality of your sleep or if
you have the symptoms of a sleep disorder, it is important to consult your
health care practitioner. He or she can help you determine the cause of your
sleep problem and recommend appropriate therapy.
DR S DESHMUKH