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| Actigraph | A biomedical instrument for the measurement of body movement. |
| Active Sleep | A term used in the phylogenetic and ontogenic literature for the stage of sleep that is considered to be equivalent to REM sleep. |
| Alpha Activity | An alpha EEG wave ofr sequence of waves with a frequency of 8-13 Hz. |
| Alpha Intrusion (-Infiltration, -Insertion, -Interruption) | A brief superimposition of EEG activity on sleep activities during a stage of sleep. |
| Alpha Rhythm | An EEG rhythm with a frequency of 8-13 Hz in human adults, which is most prominent over the parieto-occipital cortex when the eyes are closed. The rhythm is blocked by eye opening or other arousing stimuli. It is indicative of the awake state in most normal individuals. It is most consistent and predominant during relaxed wakefulness, particularly with reduction of visual input. The amplitude is variable, but typically is below 50 uV in the adult. The alpha rhythm of an individual usually slows by 0.5-1.5 Hz and becomes more diffuse during drowsiness. The frequency range also varies with age; it is slower in children and older-age groups relative to young and middle-aged adults. |
| Alpha-Delta Sleep | Sleep in which alpha activity occurs during slow wave sleep. Because alpha-delta sleep is rarely seen without alpha occurring in other sleep stage, the term alpha sleep is preferred. |
| Alpha Sleep | Sleep in which alpha activity occurs during most, if not all, sleep stages. |
| Apnea | Cessation of airflow at the nostrils and mouth lasting at least 10 seconds. There are three types of apnea: obstructive, central, and mixed. Obstructive apnea is secondary to upper airway obstruction; central apnea is associated with a cessation of all respiratory movements; mixed apnea has both central and obstructive components. |
| Apnea-Hypopnea Index | The number of apneic episodes, (obstructive, central, and mixed) plus hypopneas per hour of sleep as determined by all-night polysomnography. |
| Apnea Index | The number of apneic episodes (obstructive, central, and mixed) per hour of sleep as determined during all-night polysomnography. Sometimes a separate obstructive apnea index or central apnea index is stated. |
| Arise Time | The clock time that an individual gets out of bed after the final awakening of the major sleep episode. Distinguished from final wake-up. |
| Arousal | An abrupt change from a "deeper" stage of NREM sleep to a "lighter" stage, or from REM sleep toward wakefulness, with the possibility of awakening as the final exit come. Arousal may be accompanied by increased tonic EMG activity and heart rate as well as body movements. |
| Arousal Disorder | A parasomnia disorder presumed to be due to an abnormal arousal mechanism. Forced arousal from sleep can induce episodes. The "classical" arousal disorders are sleepwalking, sleep terrors, and confusional arousals.
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| Awakening | The return to the ploysomnographically defined awake state from any NREM or REM sleep stages. It is characterized by alpha and beta EEG activity, a rise in tonic EMG, a voluntary rapid eye movements, and eye blinks. The definition of awakenings is valid only insofar as the polysomnogram is paralleled by a resumption of a reasonably alert state of awareness of the environment. |
| Axial System | A means of stating different types of information in a systematic manner by listing on several "axes" to ensure that important information is not overlooked by the statement of a single major diagnosis. The International Classification of Sleep Disorders utilizes a three axial system: Axes A, B, and C. |
| Axis A | The first level of the International Classification of Sleep Disorders axial system on which the sleep disorder diagnoses, modifiers, and associated code numbers are stated. |
| Axis B | The second level of the International Classification of Sleep Disorders axial system on which the sleep-related procedures and procedure features, and associated code numbers are stated. |
| Axis C | The third level of the International Classification of Sleep Disorders axial system on which ICD nonsleep diagnoses and associated code numbers are stated. |
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| Baseline | The typical or normal state of an individual or of an investigative variable prior to an experimental manipulation. |
| Bedtime | Defined as the clock time when one attempts to fall asleep, as differentiated from the clock time when one gets into bed. |
| Beta Activity | A beta EEG wave sequence of waves with a frequency of greater than 13Hz. |
| Beta Rhythm | An EEG rhythm 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. The amplitude of beta rhythm is variable but usually is below 30uV. This rhythm may be drug induced. |
| Brain Wave | Use of this term is discouraged. Term suggested: EEG wave. |
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| Cataplexy | A sudden decrement in muscle tone and loss of deep tendon reflexes leading to muscle weakness, paralysis, or postural collapse. Cataplexy usually is precipitated by an outburst of emotional expression-notably laughter, anger, or startle. One of the tetrad of symptoms of narcolepsy. During cataplexy, respiration and voluntary eye movements are not compromised. |
| Cheyne-Stokes Respriation | A breating pattern characterized by regular "crescendo-decrescendo" fluctiuations in respiratory rate and tidal volume. |
| Chronobiology | The science relating to temporal, primarily rhythmical, processes in biology. |
| Circadian Rhythm | An innate daily fluctuation of physiological or behavioral functions, including sleep-wake states generally tied to the 24-hour daily dark-light cycle. Sometimes occurs at a measurably different periodicity (e.g., 23 or 25 hours) when light/dark and other time cues are moved. |
| Circasemidian Rhythm | A biological rhythm that has a period length of about 12 hours. |
| Conditioned Insomnia | An insomnia that is produced by the development, during earlier experience of sleeplessness of conditioned arousal. Causes of the conditioned stimulus can include the customary sleep environment or thoughts of disturbed sleep. A conditioned insomnia is one component of psychophysiological insomnia. |
| Constant Routine | A chronobiological test of the endogenous
pacemaker that involves a 36-hour baseline monitoring period, followed by a 40-hour waking episode of monitoring
with the individual on a constant routine of food intake,
position, activity and light exposure. |
| Cycle | Characteristic of an event exhibiting rhythmic fluctuations. One cycle is defined as the activity from one maximum or minimum to the next. |
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| Deep Sleep | Common term for combined NREM stages 3
and 4 sleep. In some sleep literature, deep sleep is applied
to REM sleep because of its high awakening threshold or
nonsignificant stimuli. See “Intermediary” Sleep Stage. |
| Delayed Sleep Phase | A condition that occurs when the
clock hour at which sleep normally occurs is moved back in time within a given 24-hour sleep-awake cycle. This results
in a temporarily displaced, that is, delayed occurrence of
sleep within the 24-hour cycle. The same term denotes a
circadian rhythm sleep disturbance, called the delayed sleep
phase syndrome. |
| Delta Activity | EEG activity with a frequency of less than
4 Hz (usually 0.1 - 3.5 Hz). Inhuman sleep scoring, the maximum characteristics for scoring delta waves is conventionally 75 uV (peak-to-peak) amplitude, and 0.5-second duration (2 Hz) or less.
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| Delta Sleep Stage | Indicative of the stage of sleep in which
EEG delta waves are prevalent or predominant (sleep stages
3 and 4, respectively). See Slow Wave Sleep. |
| Diagnostic Criteria | Specific criteria established in the lntenational Classification of Sleep Disorders to aid in determining the unequivocal presence of a particular sleep disorder.
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| Diurnal | Pertaining to the daytime. |
| Drowsiness | A state of quiet wakefulness that typically oc-
curs prior to sleep onset. If the eyes are closed, diffuse and slowed alpha activity usually is present which then gives way to early features of stage 1 sleep. |
| Duration Criteria | Criteria established in the International
Classification of Sleep Disorders for determining the duration of a particular disorder as acute, subacute, or chronic. |
| Dyssomnia | A primary disorder of initiating and maintaining sleep or of excessive sleepiness. The dyssomnias are disorders of sleep or wakefulness per se; not a parasomnia. |
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