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Information Society Technologies (IST)
Sixth EU Framework Programme for Research and Technological Development (FP6)
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An actigraph is a small wrist-worn instrument that records activity of the arm and stores the number of movements in a memory usually on a one-minute bases. The movement density can be used to estimate sleep duration sleep latency, and sleep efficiency (quality). It can also measure overall physical activity (for ergonomics or stress) as well as tremor. Absence of movement over several minutes is a relatively reliable indicator of sleep and can, perhaps in combination with hear rate, be used to provide good estimates of sleep as well as estimates of stress, corrected for physical activity.
Alpha activity
The presence of alpha waves or alpha rhythm (i.e., electrical oscillations in the alpha frequency) in the EEG of humans. See Alpha rhythm.
Alpha Rhythm
An EEG brainwave produced when an individual is in a relaxed awake condition with their eyes closed. The frequency is 8-13 Hz in human adults, and is predominately present in the occipital lobe of the brain. It indicates the awake state in most normal individuals.
Cessation of breathing for 10 or more seconds during sleep. There are two basic types of sleep apnea: Obstructive Apnea is caused by a closure of the air passage despite efforts to breathe; Central Apnea is a lack of effort to breathe. Obstructive Sleep Apnea is by far the most common type. True apnea during wakefulness is extremely rare.
Ambulatory Monitor
Portable system used for the continuous recording of multiple physiological variables during sleep.
An abrupt change from a "deep" stage of NREM sleep to a "lighter" stage, or from REMS to awake, with the possibility of awakening as the final outcome. Arousal may be accompanied by increased tonic EMG activity and heart rate, as well as body movements.
Awakening (full arousal)
The return to the polysomnographically defined awake state from any of the NREM stages or REMS: characterized by alpha and beta waves, rise in tonic EMG, voluntary REMS, and eye blinks. This definition of awakening is valid only insofar as the polysomnogram is matched by a resumption of a reasonably alert state of consciousness.
Beta rhythm (-waves, -activity)
EEG frequency in the range of 13-35 Hz; when the predominant frequency, beta rhythm is usually associated with alert wakefulness or vigilance and is accompanied by a high tonic EMG.
A sudden, dramatic decrement in muscle tone and loss of deep reflexes leading to muscle weakness, paralysis, or postural collapse: usually precipitated by an outburst of emotional expression-notably laughter, startle, or sudden physical exercise; one of the tetrad of symptoms of narcolepsy. During cataplexy, respiration is not compromised.
Any periodicity that is near but not necessarily exactly 24 hours.
Circadian rhythm
An innate, daily, fluctuation of physiological and behavioral functions, including sleep waking, generally tied to the 24 hour day-night cycle but sometimes to a measurably different (e.g., 23 or 25 hour) periodicity when light/dark and other time cues are removed.
Continuous Positive Airway Pressure (CPAP) Machine
Medical device used to treat sleep apnea. This apparatus provides a highly effective, non-invasive therapy that eliminates blockages and prevents collapse of the upper airway by generating a prescribed level of air pressure that maintains airway patency during sleep. Air pressure is delivered through a hose to a mask that fits over the nose, or both nose and mouth. The mask is secured on the face by headgear that is worn over the head. The appropriate air pressure level is determined during a "CPAP titration" sleep study. The complete system consists of a programmable pressure generator, tubing, mask and headgear. Sometimes referred to as nCPAP (nasal Continuous Positive Airway Pressure).
Delta waves
EEG activity with a frequency of less than 4 Hz. In human sleep scoring, the minimum characteristics for scoring delta waves is conventionally 75 uV (peak-to-peak) amplitude, and 0.5 second duration (2 Hz).
Excessive daytime sleepiness or somnolence
A subjective report of difficulty in maintaining the awake state, accompanied by a ready entrance into sleep when the individual is sedentary; may be quantitatively measured by use of subjectively defined rating scales of sleepiness.
A feeling of tiredness or weariness usually associated with performance decrements.
Excessive or prolonged sleep. Sometimes associated with difficulty in awakening or sleep drunkenness.
Lack of an adequate amount of oxygen in the blood.
A deficiency of oxygen reaching the tissues of the body.Insomnia - Difficulty with falling asleep or staying asleep.
Difficulty in sleeping. A confusing term-though ubiquitously employed because it is used to indicate any and all gradations and types of sleep loss.
"Light" sleep stage
Common term for NREM stage I (and sometimes stage 2).
A period lasting up to a few seconds during which the polysomnogram suddenly shifts from waking characteristics to sleep and external stimuli are not perceived; associated with excessive daytime sleepiness and automatic behavior, which are symptoms of DOES.
Muscle Tone
The amount of tension in a muscle.
A sleep disorder characterized by excessive sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations, and an abnormal tendency to pass directly into REM sleep from wakefulness. It was recently found to be caused by an abnormal gene in the brain.
"Of the night;" pertains to events that happen during sleep or the hours of darkness.
Obstructive Sleep Apnea
Repetitive cessation of breathing during sleep for 10 seconds or more due to complete closure (collapse) of the throat. Usually characterized by snoring, excessive daytime sleepiness, and other symptoms of fatigue.
Not a disorder of sleep or wakefulness per se; rather, an event happening during sleep, or induced or exacerbated by sleep, such as sleepwalking or asthma; not a dyssomnia.
Periodic Limb Movement Disorder
Also known as Periodic Leg Movements of Sleep and Nocturnal Myoclonus. Characterized by periodic episodes of repetitive limb movements during sleep. The movements are often associated with a partial arousal or awakening; however, the patient is usually unaware of the limb movements or frequent sleep disruption. . There can be marked night-to-night variability in the number of movements.
The continuous and simultaneous recording of physiological variables during sleep, i.e., EEG, EOG, EMG (these are the three basic stage scoring parameters), EKG, respiratory air flow, respiratory excursions, lower limb movement, and other electrophysiological variables.
A biomedical instrument for the measurement of multiple physiological variables of sleep. It records the sleep physiological parameters of EEG, EOG, EMG, EKG, respiratory airflow, respiratory movements, leg movements, and other parameters depending on the situation.
Pedunculopontine Tegmental Nuclei (PTN)
PTN is part of the reticular activating system involved in arousals from sleep due to, for example, sleep apnea.
Pulse Transit Time (PTT)
PTT is a noninvasive marker of blood pressure and, therefore, subcortical arousal. Blood pressure elevation, associated with respiratory arousal from sleep, results in a drop in the PTT.
REM Sleep (Rapid Eye Movement Sleep)
The sleep stage in which vivid dreaming occurs; identified by the occurrence of rapid eye movements under closed eyelids, motor atonia and low voltage EEG patterns. Also associated with bursts of muscular twitching, irregular breathing, irregular heart rate, and increased autonomic activity.
Restless Legs Syndrome
The sleep disorder characterized by tingling, creeping, crawling, or aching sensation in the legs that tends to occur when an individual is not moving. There is an almost irresistible urge to move the legs that relieve the sensations. Inability to remain at rest can result in severe sleep disturbance.
Seasonal Affective Disorder (SAD)
A mood disorder occurring in the winter months characterized by diminished energy, hypersomnia, overeating and depressed mood. Exposure to bright light in the morning hours may be effective in alleviating or decreasing symptoms.
Drugs that tend to calm, reduce nervousness or excitement, and foster sleep onset.
Working during times other than the conventional daytime hours of 9:00 a.m. to 5:00 p.m.
Overall state in which an individual rests quiescently in a recumbent position, disengages from the environment, and become unresponsive to stimuli.
Sleep Apnea
Cessation of breathing for 10 or more seconds during sleep. There are two basic types of sleep apnea: Obstructive Apnea is caused by a closure of the air passage despite efforts to breathe; Central Apnea is a lack of effort to breathe. Obstructive Sleep Apnea is by far the most common type.
Sleep Architecture
The sequence and duration of each sleep stage and awakening during a sleep period. Often displayed in the form of a histogram.
Sleep Deprivation
An acute or chronic lack of sufficient sleep, which causes a person to feel unrefreshed during wakefulness.
Sleep Disorders
A broad range of illnesses arising from many causes, including; dysfunctional sleep mechanisms, abnormalities in physiological functions during sleep, abnormalities of the biological clock, and sleep disturbances that are induced by external factors.
Sleep Episode
A total interval of sleep that may be voluntary or involuntary.
Sleep Fragmentation
Brief arousals that occur throughout the night, that reduce the total amount of time spent in the deeper levels of sleep. Frequent episodes of sleep fragmentation lead to sleep deprivation.
Sleep Inertia
Feelings of grogginess and sleepiness that persist up to 20 minutes after waking up. This results in poor performance upon awakening.
Sleep Onset
The time from when a person attempts to fall asleep until the onset of sleep. This sleep onset normally leads to NREM stage 1 sleep, but in certain conditions, such as infancy and narcolepsy, may lead to REM stage sleep.
Sleep Stages
Distinctive stages of sleep as demonstrated by EEG patterns. See Stages 1-4; REM Sleep.
Sleep Stage 1 (NREM Stage 1)
A stage of NREM sleep that ensues directly from the awake state. Its criteria consist of a low-voltage EEG tracing with well defined alpha activity and theta frequencies in the 3 to 7 cps range, occasional vertex spikes, and slow rolling eye movements (SEMs), and includes the absence of sleep spindles, K complexes, and REMS. Stage 1 normally represents 4-5% of total sleep.
Sleep Stage 2 (NREM Stage 2)
A stage of NREM sleep characterized by the advent of sleep spindles and K complexes against a relatively low-voltage, mixed frequency EEG background. High voltage delta waves may comprise up to 20% of stage 2 epochs. Stage 2 usually accounts for 45-55% of total sleep time.
Sleep Stage 3 (NREM Stage 3)
A stage of NREM sleep defined by at least 20% and not more than 50% of the period consisting of EEG waves of 2 cps or slower, with amplitudes of more than 75 mV (high-amplitude delta waves). It constitutes "deep" NREM sleep, or, so-called slow wave sleep (SWS), and is often combined with stage 4 NREM sleep because of the lack of documented physiological differences between the two. It normally appears usually only in the first third of the sleep episode, and usually compromises 4-6% of total sleep time.
Sleep Stage 4 (NREM Stage 4)
All statements concerning NREM sleep stage 3 apply to stage 4 except that high-voltage, slow EEG waves cover 50% or more of the record. NREM sleep stage 4 usually represents 12-15% of total sleep time. Sleepwalking, sleep terrors, and sleep-related enuresis episodes generally start in stage 4 or during arousals from this stage.
Sleepiness (somnolence, drowsiness)
Difficulty in maintaining the wakeful state so that the individual falls asleep if not actively kept aroused-, not simply a feeling of physical tiredness or listlessness. See Excessive daytime Sleepiness.
Slow Eye Movements (SEM)
Slow, rolling movements of the eyes under closed eyelids that occur as one drifts to sleep in stage 1.
Theta waves
EEG activity with a frequency of 4-8 Hz, maximal over temporal cortex.