Sleep Deprivation and Sleep Disorders
- 1 Introduction
- 2 Impact of Sleep Deprivation on EEGs
- 3 Impact of Sleep Deprivation on Sleepiness
- 4 Caffeine
- 5 Impact of Sleep on Overall Health
- 6 Impact of Sleep Deprivation on Performance
- 7 Common Sleep Disorders
- 8 Medications Affecting Sleep Quality and Quantity
- 9 References
Sleep is a universal experience and it is essential for general health and survival. It has multiple functions and is important for cognition (ie the ability to think clearly, to be vigilant, alert and to pay attention) as well as memory consolidation and emotional regulation. Poor quality sleep, as well as sleep loss or poorly regulated sleep, can have a negative impact on physical and mental function. It can cause sleepiness, a decline in performance, as well as affect psychological and physical functions, such as memory, learning, metabolism and immunity.
Impact of Sleep Deprivation on EEGs
Sleep research has progressed over the last few decades due to the examination of electroencephalogram (EEG) patterns that occur during sleep. This research has enabled researchers to classify sleep into various stages, and thus, provided a basis for exploring sleep abnormalities and the relationship between health and sleep.
Various changes in patterns are also evident in waking EEGs following periods of sleep deprivation. A study by Ferriera et al (2006) demonstrated that just one night of sleep deprivation resulted in specific electrophysiological changes on EEG, including increases in relative delta and theta power, as well as absolute alpha and beta power reduction.
Certain deteriorations in performance have also been noted during brief periods (lasting from between 2 and 20 seconds) on waking EEGs - at these points, the EEGs showed slow termed microwaves, which are known as ‘micro-sleeps’. Such momentary lapses are highly significant when considering the impact they can have on workers. Early concerns about public/occupational health and sleep disorders were first noted when industrial disasters such as the Exxon Valdez oil spill of 1989 were linked to sleep loss. Similarly, a health professional who does shift work, have been found to be at increased risk for occupational hazards, as well as car accidents when driving home from work.
Impact of Sleep Deprivation on Sleepiness
A dose-related increase in sleepiness, as well as a reduction in performance, occurs after sleep loss. This is highlighted in a number of ways, including physiological measures such as sleep latency (ie the onset time to sleep), subjective reporting of sleepiness and standardised behavioral testing such as reaction time. Differences are noted in both partial and complete sleep loss, as well as when sleep is broken up or “waking activities” are shifted to night-time hours (ie shift work).
Sleep debt, which accumulates when sleep is restricted, cannot be repaid. However, individuals do tend to sleep for longer periods after periods of sleep deprivation or restriction and some studies highlight the benefits of extended sleep on improving performance.
The most common psychoactive substance is caffeine. It is used to help with fatigue, to enhance performance and to prevent apnea in premature infants. However, in a recent systematic review, it has been shown to prolong sleep latency, reduce sleep length and efficiency and also to negatively impact an individual's perceived sleep quality.
It has been found that adenosine (a governing sleep factor) has an intrinsic relationship with caffeine. Their similar structure enables caffeine to bind to adenosine receptors. This blocks the adenosine receptors’ function and creates a sense of wakefulness. However, the cumulative impact of adenosine will always increase, regardless of extrinsic factors such as caffeine. Thus, people will eventually experience a sudden increase in their level of fatigue once the effects of caffeine wear off.
The effect of caffeine varies between people. Older adults’ sleep may be more sensitive to caffeine and some genetic studies have shown that certain people, particularly those carrying the cYP1a2 gene, may be more likely to experience sleep disruption secondary to caffeine intake. It is thought that an over-reliance on caffeine may be one of the biggest causes of ineffective rest in healthcare workers. Thus, timing the consumption of caffeine might be a way to enhance sleep quality, as well as ensure better regulation of sleep; restricting caffeine after 2 pm could be once such strategy.
Impact of Sleep on Overall Health
The main indicator of sleep loss is an increase in excessive daytime sleepiness. There are many causes of sleep loss, but the two key areas that result in sleep restriction are:
- Sleep disorders, such as obstructive sleep apnea (NB these disorders often go undiagnosed in large portions of the population, but they can have a significant impact on other aspects of health, such as causing high blood pressure, increasing the risk of recurrent heart attack, strokes and atrial fibrillation)
- Occupational factors such as shift work - this is particularly worrying for health workers who often complete on-call work
Sleep loss can cause a number of physical and physiological changes, which can lead to other health concerns, including:
- Type 2 Diabetes
- Sleep loss can cause alterations in glucose metabolism, including a decrease in glucose tolerance and insulin sensitivity
- An increased risk of becoming overweight due to an alteration in two key hormones
- Leptin, which is involved in appetite suppression, is not received in during sleep deprivation
- Ghrelin, the appetite-inducing hormone, is increased during sleep deprivation
- Decreased energy levels
- It has been found that recurrent sleep restriction has an impact on the function of the thyroid axis
- Elevation of cortisol levels
- This increases the likelihood of many other health issues, including anxiety, depression and other mental health conditions, as well as systemic inflammation and increased risk of cancer
- An increased concentration of inflammatory markers including C Reactive Protein (CRP)
- Eighty-eight hours of sleep deprivation or ten days of sleep restriction to four hours of sleep per night increases the concentration of the inflammatory marker C reactive protein (CRP)
- A study by Frey et al showed that one night of sleep loss (total 40 hours without sleep) triggered a stress response that included the stimulation of pro-inflammatory and anti-inflammatory proteins
- A relatively mild level of restriction of sleep of six hours per night rather than eight hours increases pro-inflammatory cytokine levels
- Affects immunological processes
- In sleep-deprived states, people experience poor antibody responses and a decline in natural killer cell activity. As discussed here, sleep is a pro-inflammatory state, but sleep restriction also leads to a pro-inflammatory state. However, the pro-inflammatory state associated with sleep restriction is not specific and results in a reduction in our ability to defend against infection. Thus, chronic sleep deprivation can be considered similar to a state of chronic stress, which has a negative impact on immune function and general health
- It is important to consider the impact of sleep on regulating inflammatory processes in relation to postoperative care. Su and Wang note that sleep disturbances have a negative impact on post-operative patients, including increased risk of delirium, increased pain sensitivity, greater cardiovascular events, and poorer recovery. Post-operative patients often report high levels of fatigue, malaise, immobility and pain. It could, therefore, be beneficial to consider if enhanced sleep might enhance postoperative rehabilitation and recovery
Impact of Sleep Deprivation on Performance
As noted above, individuals in a state of sleep deprivation will often experience reductions in performance, particularly in perceptual and motor responsiveness. Smith et al found that even moderate sleep loss resulted in compromised functioning of neural circuits involved in working-memory tasks”. Similarly, a dose-related pattern of increasingly slower times and poorer scores in assessment measures (such as the psychomotor vigilance task test) have been noted when people are subjected to sleep restrictions.
Research by Whelehan also found that sleep restriction causes declines in skill performance. This could have significant implications on health professionals, such as physiotherapists who are responsible for respiratory care such as suctioning tracheotomy patients.
Other research has found that in sleep-deprived states, people are less able to remember or interpret information correctly or make logical/ coherent decisions. These are all pertinent issues when considering clinical decision making.
Sleep deprivation will also likely have an impact on patients - it may impact their ability to recall or synthesise information into long-term memory formation. Thus, we should factor this into our management plans, particularly when providing education to patients.
The relationship between sleep deprivation and mood can also be linked to performance. Mood is significantly affected by sleep restriction, as are attention fatigue, confusion and decreases in happiness from night to morning. These alterations in state can have a major impact on patients and may decrease their willingness to engage in rehabilitation and shared decision making.
Common Sleep Disorders
According to The Diagnosis and Statistical Manual of mental disorders, or the DSM criteria, sleep disorders can be categorized as either being:
- Primary, which includes dyssomnias and parasomnias
- Secondary, which results from conditions such as mental health disorders, genetic/medical conditions, or substance-induced sleep disorders
The International Classification of Sleep Disorders provides four categories:
- Sleep disorders associated with secondary causes
- Proposed sleep disorders
Dyssomnias are characterised by either hypersomnolence (excessive sleepiness) or insomnia (a difficulty falling asleep). They can be caused by stress, caffeine, physical discomfort, the over-reliance on daytime napping or early bedtimes. (WEB) There are three main causes of dyssomnias:
- Intrinsic means (i.e. arising from within the body) - which include conditions such as idiopathic insomnia, narcolepsy and obstructive sleep apnea
- Extrinsic means (i.e. secondary to environmental or pathological conditions) - which include causes such as inadequate sleep hygiene, altitude insomnia, stimulant dependent sleep disorder and alcohol-dependent sleep disorder
- Circadian Rhythm disruption - which includes conditions such as shift work sleep disorder, and jet lag syndrome
Insomnia is classified as almost daily complaints of insufficient sleep or not feeling rested after sleep. It is one of the most common sleep disorders. It is more common in women and its prevalence ranges from 10-30%.
Hypersomnia is independent of insomnia and it refers to excessive sleepiness - individuals with hypersomnia will usually experience regular daytime sleep episodes (i.e. an increased need for daytime naps).
Narcolepsy has a similar presentation as hypersomnia but is categorised as sudden and uncontrollable sleep attacks. These attacks must occur daily over a period of one year, over a period of at least three months to be classified as narcolepsy. The usual cause of most cases of narcolepsy is a loss of neurons that produce hypocretin. Hypocretin is the neuropeptide that regulates arousal, wakefulness and appetite. There are four cardinal symptoms of narcolepsy:
- Cataplexy, which is the sudden bilateral loss of muscle tone usually occurring after experiencing a strong emotion
- Sleep paralysis, which is when an individual remains aware of his / her surroundings, but is unable to move
- Hypnagogic hallucinations, which are sensations that are imagined, but that feel real
- Automatic behavior, which is when an individual does something without thinking about it and is unable to recall doing it
Sleep apnea is another common dyssomnia. It is a physiological disorder where reduced muscle tone causes blockages in air passages. This results in apnea, which is the cessation of breathing for ten or more seconds and leads to a brief period of waking from sleep.
Sleep apnea may be caused by decreased levels of serotonin in the Hypoglossal Nucleus, but it is also commonly seen in patients who are overweight. It is typically treated using continuous positive airway pressure (CPAP) and lifestyle changes.
The final cause of insomnias is circadian rhythm disorders. These disorders result in delayed sleep phase types (i.e. sleep onset is delayed, persistent late awakening). These changes can be caused by shift work or jet lag.
Parasomnias are unwanted movements or behaviours that mainly occur during sleep. Skeletal muscle activity and autonomic nervous system changes are common. They are generally divided into four groups:
- Arousal disorders (sleep-walking, also known as somnambulism, and sleep terrors)
- Sleep-wake transition disorders (sleep talking and nocturnal leg cramps)
- Parasomnias of rapid eye movement or REM sleep (nightmares and sleep paralysis)
- Non-specific parasomnias (bruxism (grinding teeth) and paroxysmal dystonia (twisting and turning at night time), as well as that enuresis (involuntary urination at night)
Sleep terrors, which are abrupt autonomic arousals from a deep sleep, are typically associated with post-traumatic stress disorder and general anxiety. Their peak prevalence is between 3 and 7 years.
Sleepwalking may involve a patient acting out their dreams. It has a high lifetime prevalence and occurs more commonly in males than in females in adulthood.
A REM sleep disorder is similar to sleepwalking. It is a neurological condition and patients will complain of violent/ injurious behaviour during their sleep. It causes disruption of sleep and increased motor activity during dreaming. It may occur as many as several times a night or as infrequently as once every three months. Common behaviours include arm flailing, punching and kicking, as well as vocalisations.
Sleep Disorders Associated with Secondary Causes
The third category of sleep disorders results from mental illness (eg psychosis, mood disorders, anxiety, panic and alcoholism), neurological disorders (eg dementia, Parkinson's and cerebral degenerative disorders), and other medical conditions (eg COPD, asthma, gastroesophageal reflux and fibromyalgia).
Unknown Sleep Disorders
These may include shorter sleepers, longer sleepers, and night sweats (sleep hyperhidrosis) and sub-wakefulness syndrome. These conditions are usually diagnosed through a “rule-out” approach rather than a “rule-in” approach.
Medications Affecting Sleep Quality and Quantity
Various medications can have a significant impact on the quality and quantity of sleep. These include:
- Antiarrhythmics for heart rhythm problems
- Beta-blockers for high blood pressure
- Clonidine for high blood pressure
- Corticosteroids for inflammation or asthma
- Diuretics for high blood pressure
- Cough, cold and flu medication that contain alcohol
- Headache and pain medications that contain caffeine
- Nicotine replacement products
- Sedating anti-histamines
- Selective Serotonin Reuptake Inhibitors for depression and anxiety
- Sympathomimetic stimulants for Attention Deficit Disorder and thyroid hormone for Hypothyroidism
There are also a number of medications used to treat sleep disorders. However, their use must be clinically indicated as they can have more negative than positive effects in non-clinical populations. These medications include:
- Anti-parkinsonian drugs such as dopamine agents
- Benzodiazepines, and hypnotics
- Melatonin receptor stimulators
- Anti-anxiety medications
- Orexin receptor antagonists
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