What are sleep disorders?
Sleep is more than the absence of wakefulness. While a person sleeps, the brain continues to be quite active—indeed, this activity is essential for human survival. Brain activity can be measured in sleeping subjects and has been used to classify sleep into stages 1 through 4, where stage 1 is the lightest sleep and stage 4 is the deepest. A sleeper moves from stage 1, through stages 2 and 3, and to stage 4, and then back through stages 2 and 3 to stage 1. This cycle occurs every ninety to one hundred minutes throughout the night. During the latter part of the sleep period, stage 1 sleep is associated with brain activity that is as intense as that seen in waking subjects. During these periods of intense brain activity, rapid eye movements (REMs) are observed, and as a result these periods are referred to as REM sleep, and the other sleep stages are referred to as non-REM sleep. Although the precise function of sleep is still hotly debated in scientific circles, most people can verify from experience that adequate sleep has a major impact on their ability to function effectively and on their emotional stability. For those who suffer from a sleep disorder, life can become a daily struggle; sleep disorders often have severe physical, financial, and social consequences.
Patients who are having difficulty with sleeping usually complain of insomnia, feeling sleepy during the day, or abnormal behaviors during sleep. Sleep disorders have been divided into four broad categories by the Association of Sleep Disorders Centers: the insomnias, or disorders of initiating or maintaining sleep; the hypersomnias, or disorders of excessive sleep; disorders of the sleep-wake cycle; and the parasomnias, or disorders of partial arousal such as sleepwalking and night terrors. Of these, the most common complaint are the insomnias.
Insomnia is a subjective complaint of nonrefreshing sleep. Patients believe that their ability to function during the day is impeded by short or poor-quality sleep. Since most people experience transient insomnia at various times in their lives, chronic insomnia is defined as insomnia lasting longer than three months. Individuals with insomnia have a variety of sleep patterns: Some may require a long period to fall asleep, some wake up after a few hours and cannot fall asleep again, and some may not know that they have awakened briefly hundreds of times during the night. The sleep patterns of the insomniac can vary from night to night, which increases the anxiety of the patient. Electrical monitoring of brain activity shows that most insomniacs have only a slightly reduced total sleep time, with few changes in sleep stages. Physiologically, poor sleepers have been shown to maintain a higher body temperature during sleep than normal sleepers, which may reflect a higher level of arousal. Insomnia is not a necessarily disorder in itself; instead, it can be a symptom of a large number of underlying disorders. These can be physiological, psychological, or behavioral in nature, or they can be a normal part of the aging process.
Insomnia can be caused by medical problems that interfere with breathing, such as sleep apnea, in which patients have multiple episodes each night when they stop breathing. A single episode can last ten seconds to two minutes, and in some severe cases, up to 50 percent of sleep time can be spent without breathing. Sleep apnea is often seen in obese men and women because of obstruction of the air passage. Clinical signs include irregular snoring and daytime sleepiness. Insomnia can also be caused by neurological problems, muscular problems, or conditions that cause pain. Periodic leg movement can (but does not always) cause multiple awakenings during the night, as can a related disorder called restless leg syndrome, which is characterized by a creeping sensation in the legs. Psychiatric research has demonstrated that insomnia can be a symptom of clinical depression. Surveys have shown that insomniacs have a higher level of stress, tension, and anxiety than normal sleepers. In addition, insomnia can occur when behavioral patterns do not encourage sleep. The use of caffeine or engaging in arousing activities just prior to bedtime can contribute to poor sleep. The normal aging process usually causes a decrease in total sleep time, in stage 1 sleep, and an increase in fragmented sleep, resulting in drowsiness and sometimes depression in the elderly.
In addition to all these causes, there are some individuals who complain of insomnia in which no abnormalities can be found. When comparing subjective reports from the patient to sleep recordings in the laboratory, there is a tendency for such insomniacs to report wakefulness even though the sleep recording indicates that the patient is sleeping normally. It appears that there are other sleep abnormalities that contribute to the quality of sleep which remain unknown.
The hypersomnias are defined by excessive daytime sleepiness (EDS) and include the group of patients who are unable to stay awake during the day. Several external circumstances can contribute to EDS, such as jet lag, shift work, medications, or some of the disorders underlying insomnia listed above. In addition, narcolepsy, a central nervous system disorder, is characterized by the overwhelming need to sleep several times a day. These sleep attacks often occur without warning. Narcoleptics can also experience cataplexy, or sudden muscle weakness when in emotionally charged situations that cause anger, laughter, or fear. They may also experience hallucinations when sleep begins or sleep paralysis upon waking that can last for several minutes. Narcolepsy affects 0.05 percent of the population and causes significant hardship to those afflicted. It can pose a danger if the person falls asleep while operating a car or when in a dangerous environment.
The daily cycle of wakefulness followed by a prolonged sleep period is controlled by circadian rhythms. People who travel across time zones or who work rotating shifts are often forced to sleep at a time when their circadian rhythm supports wakefulness and work when their circadian rhythm supports sleep. Other individuals have defects in the mechanisms that regulate circadian rhythms and may experience delayed or advanced sleep phase syndrome in which there is a shift of the normal twenty-four-hour cycle. If they follow their circadian rhythm, these patients will sleep for a normal amount of time; however, the social consequences of retiring at 7:00 p.m. or awakening at noon are prohibitive. Internal desynchronization between the sleep-wake cycle and the closely related circadian temperature cycle can also contribute to poor-quality sleep.
The parasomnias, or disorders of arousal, include sleepwalking and night terrors. Both of these disorders occur predominantly in childhood, although they can be experienced by adults. When brain activity is characterized by an electroencephalograph (EEG), there are elements of both wakefulness and REM sleep, often in the deepest stages (3 and 4). This finding dispels the myth that sleepwalkers are acting out dreams, since dreaming occurs during REM sleep. Sleepwalking activity can vary in length. The person usually has his or her eyes open, can respond verbally, and can move about normally. Sleepwalkers are usually aware of the environment at some level, although their judgment is impaired and they can sometimes injure themselves. Night terrors involve signs of panic such as shrieking, sweats, and frenzied movements and can be distinguished from nightmares, which involve little movement and more extensive memory. Both sleepwalking and night terrors are usually not recalled, and there is little connection between these syndromes and psychiatric disease. Both may be exacerbated by sleep deprivation, stress, fever, or medications.
One of the difficulties in diagnosing insomnia or one of the other sleep disorders is that there is much individual variability among normal sleepers in sleep needs and amount of sleep logged each night. Therefore, what may be adequate sleep for one person might cause another to report poor sleep. To determine the causes of poor sleep, a person is usually referred to a sleep clinic. There, a detailed history of the problem as well as a description of the patient’s sleep habits, lifestyle, and psychological state is recorded. Often, a description of behavior during sleep from someone who shares the bedroom can provide additional important information. Next, a polysomnogram, in which the sleeping patient is monitored with electrodes, is performed so that information on brain waves, breathing, muscle movements, and blood oxygen levels can be obtained. Sometimes this test is administered in the sleep center, and sometimes it is done in the more natural sleep environment of the person’s home using ambulatory monitoring devices. From this information, a diagnosis usually can be made and the appropriate therapy determined.
When insomnia is associated with an underlying psychiatric or medical problem, treatment usually begins with the primary problem rather than with the symptom of poor sleep. When the primary problem is solved, the sleep pattern usually returns to normal. Symptomatic treatment of the insomnia itself is provided only when the cause of the sleep disturbance cannot be treated. There are two major approaches: treatments that emphasize the use of drugs or technical aids and treatments that emphasize a change in behavior.
Although over-the-counter aids cannot improve sleep, large numbers of prescription drugs can affect sleep patterns and influence alertness during waking hours. Historically, barbiturates were administered for insomnia, but in 1970, benzodiazepines were introduced; they are now the most commonly prescribed drugs for sleeplessness. These drugs are usually taken about thirty minutes before bedtime, causing drowsiness and thus decreasing the amount of time it takes to fall asleep. Benzodiazepines alter the stages of sleep, decreasing the amount of stage 1 and REM sleep and increasing the amount of stage 2 sleep. The significance of these changes is not understood. When used alone, benzodiazepines are very safe and have few side effects; if they are combined with other drugs, however, there can be a toxic interaction. Although most people can tolerate these drugs and report no daytime grogginess, some impairment of function may exist upon waking. There is strong evidence to suggest that benzodiazepines be used for only a short period of time. With continued use (longer than thirty days), patients usually find that the drug becomes less effective unless the dosage is increased to an unsafe level. When the drug is discontinued, the original symptoms of insomnia usually recur and often a “rebound insomnia,” which is even more severe than before the drug treatment began, may be present for a brief period. Because of these limitations, these “sleeping pills” are usually given when an acute but temporary situation exists. To treat insomnia that is caused by periodic leg movements, a muscle relaxant is sometimes used. For patients whose sleep apnea is not resolved by weight reduction, mechanical devices that hold the air passage open during sleep are usually employed. Orthodontic aids or tongue retainers may provide relief, and other patients wear masks that hold the air passage open, providing a continuous airflow during sleep.
Since insomnia is often caused by poor habits that condition the sleeper to remain awake, the problem can sometimes be solved by a simple commitment to avoid naps, reduce caffeine and alcohol intake, eat light meals in the evening, reduce noise in the sleep environment, and establish a regular bedtime. Many insomniacs are so preoccupied with the fear that they will not sleep well that they become tense as bedtime approaches. These fears may sometimes be put to rest by the knowledge that sleep needs vary greatly from individual to individual. In some cases, people may not physiologically require a “normal” amount of sleep but have been convinced that they have a sleep disorder by spouses who do. Another commonly held misperception that contributes to tension is the notion that, once sleep is lost, it can never be recovered. Studies have shown that sleep-deprived humans are able to return quickly to normal sleep patterns, and therefore a few nights of poor sleep is no cause for alarm.
For those whose anxiety about sleep persists, techniques that teach people to relax their muscles or meditation to decrease mental activity may reduce this anxiety and promote sleep. Patients who experience better sleep when away from their normal sleeping location may have “learned” to associate the bedroom environment with wakefulness. To overcome this problem, stimulus control is used to try to strengthen the bedroom as a cue for sleep. This method requires that patients use the bedroom only for sleeping and go to bed only when sleepy. Most important, if they do not fall asleep within ten minutes of lying down, they should get up, go into another room, and engage in a mundane activity, coming back to the bedroom only when sleepy. This may be done several times, but the main goal is to associate the bedroom with falling asleep quickly. Regardless of the length of sleep, patients should always get up at the same time and not nap during the day. This regimen may need to be continued for several weeks in order to overcome the previous habit and requires perseverance from the patient; however, the advantage of behavioral therapy lies in the absence of the side effects caused by medication.
Excessive daytime sleepiness is usually diagnosed by a polysomnogram followed by a Multiple Sleep Latency Test. In this test, patients are allowed to fall asleep several times a day, and if sleep occurs within five minutes multiple times during the day, the diagnosis is positive. EDS is treated in different ways depending on its cause. If the cause is sleep apnea or periodic leg movements, the disorder is handled as described above. In other cases of sleep fragmentation, medication is used to prevent arousal during the night. The excessive daytime sleepiness found in narcoleptics is usually treated with drugs that act as central nervous system stimulants. Other symptoms of narcolepsy are usually treated with antidepressant drugs that suppress REM sleep. Of these, gamma hydroxybutyrate has been shown to be effective and to cause limited side effects. Short naps taken throughout the day seem to prevent many of the symptoms associated with sleep attacks.
Problems with the circadian rhythms of the sleep-wake cycle are usually not helped by medication. Instead, chronotherapy may be effective in resetting the biological clock. Over the course of two weeks, the patient’s bedtime is gradually moved forward or backward around the clock until the desired bedtime is reached. Similar effects may be seen using strong light to shift the sleep period.
The field of sleep research is still in its infancy. For most of history, sleep was not studied at all because it was difficult to characterize the process without interrupting it. Early scientists such as Lucretius, however, made observations and suggested that the motions of sleeping animals might reflect their dreams. In the early nineteenth century, sleep was viewed simply as the absence of waking, and the treatment of lethargic patients with damage to the brain stem led doctors to postulate that this area of the brain had two centers—a waking center and a sleeping center. These two centers were thought to function and communicate with each other using chemical signals. As the field of neurobiology advanced, it became possible to measure the electrical properties of the brain using an electroencephalograph. By the 1930s, numerous studies had shown that the brain remains active during sleep and that the different stages of sleep have different patterns of electrical activity. REM sleep was first observed in 1953 and was linked to dreaming. Additional brain structures in the midbrain and pons were identified that controlled REM and non-REM sleep. An understanding of the neurotransmitters, or chemical substances involved in sleeping and waking, began in the 1960s when it was discovered that neurons in the pons contained serotonin and norepinephrine. Another neurotransmitter, acetylcholine, was found in neurons that were active during REM sleep.
It is only recently that the study of sleep disorders has been recognized as a legitimate pursuit. Most of the sleep disorders mentioned here were discovered in the 1960s and 1970s, and public opinion regarding those who complain of tiredness and fatigue has only gradually shifted from disdain to understanding that there might be a real physiological cause.
This greater acceptance might be due to a growing awareness of the toll of sleep deprivation. It is now understood by medical officials that the consequences of sleep deprivation are more severe than most people realize and affect metabolism, endocrine functions, immune system function, memory, mood, and reaction time. The average adult sleeps about an hour less than the eight hours per night recommended by sleep experts. Many people often stay up later than they should because of watching television or surfing the Web. Insomnia is experienced by more than half of the adult population at some point in their lives, and more than 10 percent of the population experiences restless leg syndrome. The factors most often identified for disrupting sleep are stress and pain. Despite sleep deprivation, many people will still strive while drowsy, and some have even fallen asleep at the wheel. Sleep deprivation has also negatively impacted work performance for numerous adults. The list of work-related problems includes being late for work, making errors, reductions in the quality of work, lower productivity, diminished concentration, and suffering injuries.
Perhaps because of such statistics and a growing public recognition of the dangers of sleep problems, the number of sleep centers and laboratories that are studying sleep and its accompanying disorders has grown tremendously. These sleep centers have been instrumental in elucidating the primary disorders of sleep and in educating the general public concerning sleep management and the safety risks that result from abnormal sleep. Research laboratories are investigating the anatomical, chemical, and physiological mechanisms of sleep and sleep abnormalities. Some of the most interesting areas of research include genetic studies that determine whether sleep disorders are inherited. There appears to be a significant genetic component to several sleep characteristics, including bedtime, sleep duration, insomnia, narcolepsy, snoring, and sleep apnea. It is expected that, as scientists come to understand more about the nature and mechanisms of the brain and normal sleep, further understanding of the causes and treatments for sleep disorders will be forthcoming.
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