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Epidemiology of Sleep Age, Gender, and Ethnicity

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How shall we know sleep? Since the broad adoption of polysomnography (PSG), this question is not asked often enough, and is too often answered with buoyant self-assuredness.

The scientific journey of Werner Heisenberg (Cassidy, 1992) provides some perspective on how to answer this question. Like Pavlov before him, Heisenberg was a Nobel laureate, but were that his main accomplishment, he would be lost in the oblivion of history. Pavlov achieved fame not by winning the Nobel prize for his studies of the digestive processes of dogs, but as an afterthought of that research: deriving principles of conditioning that explained the behavior of dogs and others (Windholz, 1997). Heisenberg was a German physicist, and his prize was for contributions to the theory of quantum mechanics. As part of that research program, he was frustrated in his attempts to study atomic particles because the light needed to illuminate the subject altered the path of the electrons. Thus was born Heisenberg’s Uncertainty Principle: Theact of measurement alters what one wishes to measure, rendering specific knowledge indeterminate.

Sleep scientists in the main are probably not very sympathetic to Heisenberg’s complaint. How much error could light particles have introduced to the study of electrons compared to our routine procedures? Our standard protocol is to remove individuals from their accustomedsurroundings, mount a dozen or more sets of electrodes with glue, tape, straps, clips, and the like from head to foot, and then put them to rest in an uncomfortable hospital bed. It is well established that the sleep labo-ratory setting alters sleep, as shown by disturbed sleep the first night in the laboratory (i.e., first night effect; Kales & Kales, 1984) and laboratory-home recording comparisons (Edinger et al., 1997; Stepnowsky, Moore, & Dimsdale, 2003). With the ease and confidence of a stand-up comic, the sleep technician instructs the individual to sleep naturally. Heisenberg didn’t know how good he had it.We could prove that PSG alters sleep by comparing it to a known accurate measure of sleep, but PSG is the gold standard against which other methods of sleep assessment are judged. Considering commonplace alternatives to PSG, the worthiness of actigraphy, inferring sleep from limb inactivity, or self-report (SR) sleep is evaluated by how closely they match PSG data. Of course, the matches are never perfect and assignment of fault is in part determined by convention (i.e., because PSG is objective, it is always best) and in part by philosophy of science (e.g., greater faith is assigned SR sleep in the unperturbed natural environment because it maximizes ecological validity).Perhaps we shall never know sleep, only representations of it blurred by intrusive and/or fuzzy measures. Certainly for the present, no method of measuring sleep spares the subject of our interest. The best we could aspire to is to choose a method whose profile of strengths and shortcomings seems to closely fit the circumstances and goals of a particular clinical or research evaluation. In these endeavors, we should be humbled by the implications of Heisenberg’s admonition that at all times, the relationship between sleep data and sleep is uncertain.


This epidemiological study relied on self-report (SR) data because we wanted to collect information on a large sample and using PSG or, to a lesser extent, actigraphy would have increased the survey cost enormously, would have placed a greater inconvenience burden on participants, causing greater difficulty in recruiting the desired sample, and would have dramatically extended the length of an already lengthy study due to the limited availability of assessment instrumentation.SR data have the advantages of:

Being an inexpensive, convenient source of data.
Not altering the normal sleep setting.
Not altering normal sleep routines.
Being the best available measure of subjective sleep perception.





Sleep Deprivation and Snoring

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The second half of the past century was a time of remarkable scientific expansion and knowledge explosion. Biology and health fields were the beneficiaries of many genuine observations and discoveries and, as a result, the health of individuals and the public as a whole improved markedly. The area of sleep and sleep disorders illustrates the advances in knowledge that occurred.

Related article: Sleep Deprivation Could Shave Years Off Your Life

Sleep is a topic that has long been addressed by writers-but much more frequently by poets than by researchers. As an example, in the beginning of the nineteenth century, Samuel Taylor Coleridge gave us this verse:

Oh, Sleep! It is a gentle thing,
Beloved from pole to pole

Unquestionably, during the last few decades the study of sleep and its biology in health and disease has moved to the forefront of research, and it has revealed a wealth of observations. At the same time, it has attracted the interest of many investigators with expertise in diverse basic disciplines and clinical areas.

The association of sleep disorders with other clinical fields such as cardiology, neurology, mood and attention disorders, and pneumology is well recognized. Sleep deprivation is a medical issue, but also a social one. As a consequence, we have seen a number of societal and regulatory changes to ensure that appropriate sleep time is available.

This series of monographs, Lung Biology in Health and Disease, includes a number of volumes on sleep, the first one having been published in 1984. Seven of these volumes have been exclusively about one or another aspect of sleep, and others, on different subjects, included components related to sleep. However, lack of sleep did not achieve stardom in this series until Dr. Clete Kushida from the world-famous Stanford Sleep Disorders Clinic and Research Center accepted the invitation to edit this volume on Sleep Deprivation: Basic Science, Physiology, and Behavior.

This volume and its companion on Sleep Deprivation: Clinical Issues, Pharmacology, and Sleep Loss Effects are true landmarks in the area of sleep biology and medicine. Dr. Kushida enrolled contributors who have pioneered exploration of the field, and I am grateful to them all for the opportunity to introduce this volume to the readership.



Sleep Disorders

Sleep Disorders: Diagnosis, Management and Treatment

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History of sleep medicine

Sleep and dreams have been popular throughout time for writers, researchers and physicians alike. However, most of our modern knowledge of sleep medicine was achieved only in the last four decades. There have been several breakthrough discoveries that paved the way to the scientific investigation of sleep (Table 1).

snoring is the most common cause of sleep apnea and anti snoring devices is so popular around the world.

Sleep Disorders

To date, the understanding of why we sleep and the precise sleep control mechanisms of the brain are far from being completely elucidated. Previously, it was believed that sleep is a time of quiescence and 

tranquillity, a time when the body and mind relax to recuperate from the day’s activity, a time when relatively little happens. These assumptions are partially incorrect because sleep is, in fact, an active process. At the start of the nineteenth century, the major sleep theory was that of the hypnotoxins. This theory posited that when we are awake there is an accumulation of poisonous hypnotoxin which drives sleepiness. Hypnotoxins were thought to be detoxified only during sleep. The discovery that serum from sleep-deprived dogs injected into alert dogs caused them to fall asleep (Legendre and Pieron) provided strong support for this theory.

Currently, several mediators, such as adenosine, interleukins, tumournecrosing factor, prostaglandins, lipopolysaccharides and δ-producing proteins, have been proposed to mediate the homoeostatic drive for sleep. Sleep, however, is not regulated by just homoeostatic principles. The discovery by Kleitman that, even with on-going sleep deprivation, one can be less sleepy the following morning suggested that additional factors control the drive for sleep. Indeed, the current agreement among sleep researchers is that sleep is regulated by two factors: the duration of wakefulness (homoeostatic drive to sleep) and the time of day (circadian drive to sleep). The absolute drive to sleep at any point in time is therefore the combination of these two drives.

The discovery of the electroencephalogram in 1928 by Berger provided a quantum leap for sleep research. Applying the new methods to measure EEG activity in sleeping people, or animals, revealed that the transition from wakefulness to sleep is accompanied by specific and well-characterized changes in brain wave activity (Table 2 and Figure 1). Electrocephalography (EEG) has allowed widespread investigations of brain mechanisms controlling sleep and wakefulness by several investgators, including Frederick Bremer, Moruzzi and Magoun, Michele Jouvet and others. There is still an on-going effort for further understanding of the brain circuitry participating in sleep regulation.

different stages: stage 1 (light sleep), stage 2 (consolidated sleep), and stages 3 and 4 (deep, or slow wave sleep). Division of sleep into these stages relies on three physiological variables: EEG, electromyography (EMG) and electro-oculography (EOG) as demonstrated in Table 2 and Figure 1.

The different EEG patterns that are characteristic of non-REM sleep stages are shown in Figure 1. Stage 1 is characterized by relatively low-amplitude θ activity intermixed with episodes of a activity. In stage 2 there are K-complexes (marked with an arrow) and sleep spindles (marked by underlining), whereas stages 3 and 4 are dominated by increasing amounts of slow-wave high-amplitude (δ) activity.

During normal sleep, these stages tend to occur in succession, forming a unique ‘sleep architecture’ (see Chapter 2). Generally, from wakefulness an individual falls into stage 1 sleep, followed by stages 2, 3 and 4 and REM sleep. This succession of sleep stages, culminating in REM sleep, forms a ‘sleep cycle’. The length and content of sleep cycles change throughout the night as well as with age. The relative percentage of deep sleep is highest in the first sleep cycle and decreases as the night progresses, whereas the relative length of REM sleep episodes increases throughout the course of the night. When totalling the various sleep stages through the night in normal young adults, stage 1 occupies up to 5% of the night, stage 2, 50%, and REM sleep and slow wave sleep (SWS) 20-25% each. These relative percentages change with age, as does the cycle length. In infants the normal cycle of sleep lasts about an hour, whereas in adults it lasts about 1.5 hours. Table 3 demonstrates the percentages of different sleep stages and sleep length at different ages.

Brief body movements, which may be accompanied by arousals, mark transitions to and from REM sleep. These four to eight brief awakenings, which are too short to be registered in the memory, are not considered abnormal or sleep disruption. This point is important to keep in mind when dealing with complaints about sleep. It is the difficulty in falling back to sleep, once brief awakening has occurred, rather than the awakenings themselves that may need to be treated. In some sleep disturbances, however, there is a large increase in the number of brief arousals from sleep, which indeed needs medical attention.

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