Sleep is an essential physiological function. Most of us need 7.5 to 8 hours of restful sleep at night in order to function adequately – both physically and psychologically. Normal human sleep follows a well defined cyclical pattern. We have biological circadian rhythms which make us fall asleep at night, make us briefly sleepy after lunch and keep us awake during the day. We have two distinct types of sleep: NREM (non rapid eye movements) sleep and REM (rapid eye movements) sleep. The NREM and REM sleep alternate with each other in 4 to 6 cycles. Most of the deep sleep occurs during the first third of the night and the last third is dominated by REM sleep. The first REM sleep cycle occurs about 80-110 minutes after the sleep onset.
NREM sleep is further divided into stages N1, N2 and N3 primarily based on EEG (electroencephalographic) characteristics. N1 is the lightest and N3 is the deepest NREM sleep. Stage N3 sleep is also called delta sleep, deep sleep or slow wave sleep. It is called slow wave sleep because brain activity slows down dramatically as the person progresses to N3 sleep. In normal people, N2 sleep begins after about 10 to 12 minutes of N1. The N2 sleep lasts for about 30 to 60 minutes during the first sleep cycle before the N3 makes its appearance. About 75-80% of our sleep is in the form of NREM and the rest is REM. We spend about half the night in N2 sleep. We normally wake up a few times during the night but do not always remember it.
REM sleep is characterized by rapid eye movements, loss of muscle tone (atonia) and certain EEG characteristics. The heart rhythm and breathing may become uneven. Vivid dreaming may occur.
This means an overnight sleep study. During this study the following parameters are usually recorded which help to diagnose a variety of sleep disorders:
- Electroencephalogram (EEG): This term means recording the electric current generated by the brain cells. In order to record EEG, special wires are glued to the scalp. It helps to determine how fast you fell asleep and the quality of your sleep. It also helped determine the total amount of time you sleep and how many times you wale up during the night. With the help of the EEG, we were able to determine the depth of the sleep.
- Electrooculogram (EOG): This term implies recording the movements of the right and left eye. This recording is used along with the EEG to determine when a person enters rapid eye movement sleep.
- Chin electromyogram (EMG): This term implies recording the electrical activity of chin muscles. The EMG is also used to determine when a person enters REM sleep.
- Leg electromyogram (EMG): This recording determines any movements in the legs while asleep.
- Nasal and oral airflow: This measure is used to determine the presence or absence of airflow through the nose and mouth. This helps to determine if the person has shallow breathing (called hypopnoea in medical terminology) or pauses in breathing (called apnoeas).
- Thoracic and abdominal respiratory effort: This recording is done by placing belts around the chest and belly to record the effort of breathing.
- Pulse oximetry: This term implies measurement of blood oxygen level.
- Body position: This helps determine if the person is sleeping on his back, sides or the belly.
- EKG: This term implies recording of electrical activity of the heart.
Multiple Sleep Latency Test (MSLT)
The term multiple sleep latency test implies nap tests during the day. A person is given four or five opportunities to fall asleep at pre-determined times two hours apart throughout the day. During this test, a person lies down on a bed in street clothes in a darkened room. He is given the instructions to try to fall asleep or not to resist sleep. During this test, we measure the time it takes to fall asleep after the lights are turned out and the stages of sleep during the nap. In particular, we determine if a person enters rapid eye movement sleep (REM sleep). This determination is important, because normal human beings rarely enter rapid eye movement sleep during these naps and they do not enter REM sleep during more than two of these naps.
Some Commonly Seen Sleep Disorders
Obstructive sleep apnea hypopnea syndrome: Obstructive Sleep Apnea means stoppage of breathing due to a temporary obstruction in the throat during sleep. It is considered significant if it lasts for more than ten seconds at a time and occurs more than five times per hour. People with a more severe problem may stop breathing for more than three (3) minutes at a time! (The 3 minute figure is not a misprint). These spells can occur more than 100 times per hour. During these spells, there can be a severe drop in the blood oxygen level, which may decrease to values less than half the normal. The term Obstructive Sleep Hypopnea means shallow breathing during which you have partial obstruction in the throat. Hypopnea produces the same ill-effects in the body as the apnea.
Among the “middle-aged” people (age 30 to 60), about 24% men and 9% women have 5 or more spells of obstructive apnea and hypopnea per hour, but they may not be symptomatic (The New England Journal Of Medicine. April 29, 93). About 9% men and 4% women have 15 or more spells of obstructive sleep apnea and hypopnea. Most sleep specialists would consider treating individuals with this degree of breathing disturbance. About 4% men and 2% women have symptomatic obstructive sleep apnea. These people don’t feel refreshed upon waking and have excessive daytime sleepiness which interferes with day to day life.
Because of the obstruction in the throat, the breathing is noisy and labored. When the throat closes off completely it blocks off the airflow. The spouse or bedpartner may report snoring interrupted by pauses during which the person is unsuccessfully trying to inhale. Because of these pauses, there is an interruption in sleep during which the muscles in the throat start working again. The throat then suddenly becomes unblocked and there is a loud snorting or gasping noise as the air gushes into the lungs. The awakenings from sleep are generally very brief and the person may not remember them in the morning. The pauses in breathing lead to repeated decreases in blood oxygen level. The blood pressure increases at night and eventually it may begin to remain elevated during the day. The heart muscles have to work harder against the increased pressure in the chest during these apneic spells. This may lead to heart failure over the years. The heart may slow down or stop altogether for several seconds during the apneic spells. The heart beat can become dangerously irregular due to sleep apnea. The heart rhythm problems may be the cause of death during sleep in the case of some people.
Restless Legs Syndrome (RLS): Restless legs syndrome is a disorder characterized by disagreeable leg sensations that usually start prior to sleep onset and that cause an irresistible urge to move the legs. The sensation generally affects the lower legs but be felt in feet, thighs, arms and even the genitals. There is the partial or complete relief of the sensation with leg motion and the return of the symptoms upon cessation of the movements. The sensations and associated leg movements may interfere with sleep onset and may be present if the person wakes up during the night. The RLS episodes are more likely to occur between 10 pm to 4 am. The sensations are usually described as aching discomfort, creeping, crawling, pulling, pricking, tingling, or itching etc. As many as two third of patients have a family history of a similar condition. At least 80% of RLS patients also experience periodic limb movements (see below). About a third of the patients with periodic limb movements have restless legs. In addition, patients may have periodic and aperiodic limb movements while awake and at rest.
About 2% of children ages 8 to 17 have RLS symptoms. The majority of these children have a parent with RLS. These children may have attention deficit disorder type symptoms.
20% pregnant women report having RLS and it may be related to iron and vitamin deficiency. The condition usually goes away within a few weeks after delivery. Women with postpartum depressive symptoms had higher prevalence of excessive daytime sleepiness and restless legs in last trimester of pregnancy,
Iron deficiency, even at a level too mild to cause anemia, has been linked to RLS in some people. This can be confirmed by doing a blood test called ferritin level. The ferritin should be maintained at value greater than 100 mcg/L.
The RLS may be seen in patients with obstructive sleep apnea and may not respond to treatment till the sleep apnea is adequately treated.
RLS may be seen more frequently in association with certain medical conditions such as chronic kidney disease (uremia), kidney dialysis, diabetes, magnesium deficiency, folate deficiency, hypothyroidism, varicose veins, osteoarthritis, rheumatoid arthritis, fibromyalgia, alcoholism, depression, attention deficit disorder, narcolepsy, Parkinson’s disease, multiple sclerosis, migraine with aura, brain injury, spinal cord injury, peripheral neuropathy and certain muscle conditions.
Certain medications including antidepressants, antipsychotics, certain blood pressure pills, metoclopramide, diuretics, asthma drugs, antihistamines and decongestants may cause RLS.
Good sleep hygiene, exercise, and avoidance of alcohol and caffeine may help. Heavy exercise in the evening may worsen RLS. Treatment with medications is very helpful in most cases of RLS. The anti-Parkinson’s drugs that are used for RLS may become counterproductive and augment the condition with long term use for 6% people. The term augmentation means worsening of RLS and the restlessness may start to occur earlier in the evening or in afternoon.
Periodic Limb Movements Disorder (PLMD): Some people have repeatedly jerking in legs or arms during sleep. In the morning they awake feeling tired and they are sleepy during the day. This disorder can be diagnosed in a sleep laboratory. The disorder may be totally asymptomatic but can produce anxiety and depression related to the chronicity of the sleep disturbance. There is growing scientific evidence that the periodic limb movements contribute to high blood pressure and cardiovascular disease. If it is felt necessary to treat the periodic limb movements, medications are helpful in most cases.
Narcolepsy: People with narcolepsy fall asleep unexpectedly many times during the day. Not only can this be embarrassing, but it can be very dangerous. The excessive sleepiness of narcolepsy is characterized by repeated episodes of naps or lapses into sleep of short duration. The narcoleptic patient typically sleeps for 10 to 20 minutes during these naps and awakens refreshed but within the next two to three hours begins to feel sleepy again and the pattern repeats itself. The sleep usually occurs in situations in which sleepiness is common: such as traveling in automobile or airplane, meetings, lectures, watching TV or movie, or in theater. The patients may be able to tolerate the sleepiness for a period of time. Eventually, however, it is impossible to combat the sleepiness. There may be sudden and irresistible sleep attacks in situations where sleep normally never occurs, including: during an examination, during conversation and while eating, walking, or driving. Narcolepsy is a central nervous system disorder due to deficiency of a chemical called hypocretin or orexin. It is typically associated with cataplexy (muscle weakness with strong emotions), sleep paralysis and hypnagogic (at sleep onset) or hypnopompic (at sleep offset) hallucinations. A daytime study called a Multiple Sleep Latency Test (MSLT, see below) can help confirm the presence of narcolepsy. The MSLT should be performed after a night in the sleep lab. The night study documents that there is not another sleep disorder causing your daytime sleepiness. MSLT’s are performed to examine your degree of daytime sleepiness. MSLT demonstrates that the mean sleep latency (time it takes to fall asleep) is less than 5 to 8 minutes. People with narcolepsy typically enter REM sleep during two or more MSLT naps. An occasional person may need MSLT on 4 separate days to convincingly rule out narcolepsy.
Idiopathic Hypersomnia: It is a disorder of central nervous system that is associated with a normal or prolonged nighttime sleep episode and excessive sleepiness consisting of prolonged (1 to 2 hour) daytime naps consisting of NREM sleep. The excessive daytime sleepiness is worsened in situations during which sleepiness is common: after meals (especially lunch), traveling in automobile or airplane, meetings, lectures, watching TV or movie and in theater etc. You may be able to awaken the person normally but some patients report great difficulty waking up and experience disorientation after awakening. Some patients may have sleep attacks like the people with narcolepsy. Naps are usually longer than in narcolepsy or sleep apnea, and short naps are generally reported as being nonrefreshing. MSLT demonstrates that the mean sleep latency (time it takes to fall asleep) is less than 5 to 8 minutes. People with idiopathic hypersomnia do not enter REM sleep more than once during the MSLT naps.
Sleep Walking: Sleepwalking consists of a series of complex behaviors during slow-wave sleep and result in walking during sleep. Episodes can range from simple sitting up in bed to walking and even to apparent frantic attempts to “escape.” The patient may be difficult to awaken but, when awakened, often is mentally confused. The patient usually has no memory of the episode’s events. Sleepwalking can include inappropriate behavior, such as urinating in a closet, and these behaviors are especially common in children. Sleepwalking can result in falls and injuries. Physical harm can result from the attempt to “escape” or simply from walking into dangerous situations. Rarely, homicide or suicide during apparent sleepwalking episodes have been reported. The person attempting to awaken the patient can be violently attacked. Sleep walking is a treatable condition.
Sleep Terrors: These are characterized by a sudden arousal from stage 3 or 4 sleep with a piercing scream or cry, accompanied by intense fear. The person has rapid heart beat, rapid shallow breathing and sweating. The patient usually sits up in bed, usually can not be awakened, and, if awakened, is confused and disoriented. Usually there is no memory of the event, although sometimes the patient may report very brief vivid dream images or hallucinations. The episode may be accompanied by incoherent speech or loss of bladder control
Rem Sleep Behavior Disorder (RBD): This is characterized by the intermittent loss of REM sleep electromyographic (EMG) atonia and by the appearance of elaborate motor activity associated with dreams. Punching, kicking, leaping, and running from the bed during attempted dream enactment are frequent manifestations and usually correlate with the reported dream imagery. Medical attention if often sought after injury has occurred to either the person or bed partner. Occasionally, a patient may present because of sleep disruption and excessive daytime sleepiness. Because RBD occurs during REM sleep, it typically appears at least 90 minutes after sleep onset. Violent episodes typically occur about once per week but may appear as frequently as four times per night over several consecutive nights. An acute, temporary form may accompany due to REM sleep rebound during withdrawal from alcohol and sedative-hypnotic agents. Drug-induced cases have been reported during treatment with antidepressants and other medications. There may be a prodromal history of sleep talking, yelling, or limb jerking. Dream content may become more vivid, unpleasant, violent, or action-filled coincident with the onset of this disorder. The response to treatment is very gratifying for most patients.
Shift Work: Shift work sleep disorder consists of symptoms of insomnia or excessive sleepiness that occur in relation to work schedules. The work is usually scheduled during the habitual hours of sleep. The sleep complaint typically consists of an inability to maintain normal sleep duration when trying to fall asleep in the morning after a night shift. The reduction in sleep length usually amounts to one to four hours (mainly affecting REM and stage 2 sleep). The sleep is perceived as unsatisfactory and unrefreshing. The insomnia appears despite the patient’s attempt to optimize environmental conditions for sleep. The condition usually persists for the duration of the work-shift period. Early morning work shifts (starting between 4 a.m. and 7 a.m.) may also be associated with complaints of difficulty in sleep initiation as well as difficulty in awakening. Work on permanent evening shifts can be associated with difficulties initiating sleep. Excessive sleepiness usually occurs during shifts (mainly night) and is associated with the need to nap and impaired mental ability because of the reduced alertness. Reduced alertness, which occurs not only during the work shift, may be associated with reduced performance, capacity, with consequences for safety. Also, major portions of the individual’s free time may have to be used for recovery of sleep, which in many cases will have negative social consequences such as marital disharmony and impaired social relationship. A sleep physician can provide helpful suggestions.
Chronic Insomnia: Most people have occasional trouble falling asleep, but when insomnia lasts for more than a month or it disrupts your daily activities consult your physician. Insomnia can occur due to stress, worry, anxiety, depression, chronic pain from arthritis or other diseases, medication, alcohol, caffeine and for no obvious reason.
Delayed Sleep-Phase Syndrome: This is a disorder in which the person can not fall asleep at the desired time, resulting in symptoms of sleep-onset insomnia or difficulty in awakening at the desired time. There is little or no reported difficulty in maintaining sleep once sleep has begun. Typically, the patients complain of difficulty in falling asleep until between 2 a.m. and 6 a.m. or difficulty awakening at the desired or necessary time in the morning to fulfill social or occupational obligations. Daytime sleepiness occurs depending on the degree of sleep loss that ensues due to the patient’s attempts to meet his or her social obligations by getting up “on time.” When not obliged to maintain a strict schedule (e.g. on weekends or during vacations), the patient sleeps normally but at a delayed phase relative to local time.