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| Maintenance of Wakefulness Test (MWT) | A series of measurements of the interval from “lights out” to sleep onset that is utilized in the assessment of the ability to remain awake. Subjects are instructed to try to remain awake in a darkened room while in a semireclined position. Long latencies to sleep are indicative of the ability to remain awake. This test is most useful for assessing the effects of medication upon the ability to remain awake. |
| Major Sleep Episode |
Major Sleep Episode: The longest sleep episode that occurs
on a daily basis. Typically the sleep episode dictated by the
circadian rhythm of sleep and wakefulness; the conventional
or habitual time for sleeping. |
| Microsleep | An episode lasting up to 30 seconds during
which the external stimuli are not perceived. The polysomnogram suddenly shifts from waking characteristics to sleep.
Microsleeps are associated with excessive sleepiness and automatic behavior. |
| Minimal Criteria | Criteria of the International Classification
of Sleep Disorders derived from the diagnostic criteria that
provide the minimum features necessary for making a particular sleep disorder diagnosis. |
| Montage | The particular arrangement by which a number
of derivations are displayed simultaneously in a polysomnogram. |
| Movement Arousal | A body movement associated with an
EEG pattern of arousal or a full awakening; a sleep scoring
variable. |
| Movement Time | The term used in sleep record scoring to
denote when EEG and EOG tracings are obscured for more
than half the scoring epoch because of movement. It is only
scored when the preceding and subsequent epochs are in
sleep. |
| Multiple Sleep Latency Test (MSLT) | A series of measurements of the interval from “lights out” to sleep onset that is
utilized in the assessment of excessive sleepiness. Subjects
are allowed a fixed number of opportunities to fall asleep
during their customary awake period. Excessive sleepiness is
characterized by short latencies. Long latencies are helpful
in distinguishing physical tiredness or fatigue from true sleepiness.
Muscle Tone: A term sometimes used for resting muscle
potential or resting muscle activity. See Electromyogram
(EMG). |
| Myoclonus | Muscle contractions in the form of abrupt "jerks"
or twitches generally lasting less than 100 milliseconds. The
term should not be applied to the periodic leg movements
of sleep that characteristically have a duration of 0.5 - 5 seconds. |
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| Nap | A short sleep episode that may be intentionally or
unintentionally taken during the episode period of habitual
wakefulness. |
| Nightmare | Used to denote an unpleasant and frightening
dream that usually occurs in REM sleep. Occasionally called
a dream anxiety attack, not a sleep (night) terror. Nightmare
in the past has been used to indicate both sleep terror and
anxiety dream attacks. |
| Nocturnal Confusion | Episodes of delirium and disorientation close to or during nighttime sleep; often seen in the elderly and indicative of organic central nervous system deterioration. |
| Nocturnal Dyspnea | Respiratory distress that may be minimal during the day, but becomes quite pronounced during sleep. |
| Nocturnal Penile Tumescence (NPT) | The natural periodic
cycle of penile erections that occur during sleep, typically
associated with REM sleep. Preferred term: sleep-related
erections. |
| Nocturnal Sleep | Indicative of the typical “nighttime” or
major sleep episode related to the circadian rhythm of sleep
and wakefulness; the conventional or habitual time for sleeping. |
| Non-Rapid Eye Movement (NREM, Non-REM) Sleep | See
Sleep Stages. |
| NREM Sleep Intrusion | An interposition of NREM sleep,
or a component of NREM sleep physiology (e.g., elevated
EMG, K complex, sleep spindle, delta waves), in REM sleep,
a portion of NREM sleep not appearing in its usual sleep
cycle position. |
| NREM-REM Sleep Cycle (Synonymous with Sleep Cycle) | A period during sleep composed of a NREM sleep episode
and the subsequent REM sleep episode; each NREM-REM sleep couplet is equal to one cycle. Any NREM sleep stage suffices as the NREM sleep portion of a cycle. An adult sleep
period of 6.5-8.5 hours generally consists of four to six cycles.
The cycle duration increases from infancy to young adulthood. |
| NREM Sleep Period | The NREM sleep portion of NREM-REM sleep cycle; such an episode consists primarily of sleep
stages 3 and 4 early in the night and of sleep stage 2 later.
See Sleep Cycle; Sleep Stages. |
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| Obesity-Hypoventilation Syndrome | A term applied to obese
individuals who hypoventilate during wakefulness. Because
the term can apply to several different disorders, it is dis-
couraged from use. |
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| Paradoxical Sleep | Synonymous with REM sleep, which is
the preferred term. |
| Parasomnia | Disorder of arousal, partial arousal or sleep
stage transition. It represents an episodic disorder in sleep
(such as sleepwalking) rather than a disorder of sleep or wake-
fulness per se. May be induced or exacerbated by sleep; not
a dyssomnia. |
| Paroxysm | Phenomenon of abrupt onset that rapidly attains
a maximum and terminates suddenly; distinguished from
background activity. Commonly refers to an epileptiform
discharge on the EEG. |
| Paroxysmal Nocturnal Dyspnea (PND) | Respiratory dis-
tress and shortness of breath due to pulmonary edema, which
appears suddenly and often awakens the sleeping individual. |
| Penile Buckling Pressure | The amount of force applied to
the glans of the penis sufficient to produce at least a 30 degree
bend in the shaft. |
| Penile Rigidity | The firmness of the penis as measured by
the penile buckling pressure. Normally, the fully erect penis
has maximum rigidity. |
| Period | The interval in time between the recurrence of a
defined phase or moment of a rhythmic or periodic event,
that is, between one peak or trough and the next. |
| Periodic Leg Movement (PLM) | A rapid partial flexion of
the foot at the ankle, extension of the big toe, and partial flexion of the knee and hip that occurs during sleep. The movements occur with a penodicity of 20-60 seconds in a stereotyped pattern lasting 0.5-5.0 seconds and are a characteristic feature of the periodic limb movement disorder. |
| Periodic Movements of Sleep (PMS) | See Periodic Leg Movement. |
| Phase Advance | The shift of an episode of sleep or wake to
an earlier position in the 24-hour sleep-wake cycle; e.g., a
shift of the sleep phase by 3 hours from 11 p.m.-7 a.m. to
8 p.m.-4 a.m. represents a 3-hour phase advance. See Phase Delay |
| Phase Delay | A shift of an episode of sleep or wake to a
later time of the 24-hour sleep-wake cycle. It is the exact
opposite of phase advance. These terms differ from common
concepts of change in clock time: to effect a phase delay, the
clock is moved ahead or advanced. In contrast, to effect a
phase advance, the clock moves backward. See Phase Advance. |
| Phase Transition | One of the two junctures of the major
sleep and wake phases in the 24-hour sleep-wake cycle. |
| Phasic Event (-Activity) | Brain, muscle, or autonomic events
of a brief and episodic nature occurring in sleep; characteristic
of REM sleep, such as eye movements, or muscle twitches,
usually the duration is milliseconds to 1-2 seconds. |
| Photoperiod | The duration of light in a light-dark cycle. |
| Pickwickian | A term applied to an individual who snores
is obese and sleepy, and has alveolar hypoventilation. The
term has been applied to many different disorders and therefore is discouraged. |
| PLM-Arousal Index | The number of sleep-related periodic
leg movements per hour of sleep that are associated with an
EEG arousal. See Periodic Leg Movement. |
| PLM Index | The number of periodic leg movements per
hour of total sleep time as determined by all-night polysomnography. Sometimes expressed as the number of movements per hour of NREM sleep because the movements are
usually inhibited during REM sleep. See Periodic Leg Movements. |
| PLM Percentage | The percentage of total sleep time occupied with recurrent episodes of periodic leg movements. |
| Polysomnogram | The continuous and simultaneous recording of multiple physiological variables during sleep, i.e., EEG, EOG, EMG (these are the three basic stage scoring parameters), EKG, respiratory air flow, respiratory movements, leg
movements, and other electrophysiological variables. |
| Polysomnograph | A biomedical instrument for the measurement of physiological variables of sleep. |
| Polysomnographic (as in -Recording, -Monitoring, -Registration, or -Tracings) | Describes a recording on paper, computer disc or tape of a polysomnogram. |
| Premature Morning Awakening | Early termination of the
sleep episode, with inability to return to sleep sometimes
after the last of several awakenings. It reflects interference at
the end rather than at the commencement of the sleep episode; a characteristic sleep disturbance of some people with depression. |
| Proposed Sleep Disorder | A disorder in which there is insufficient information available in the medical literature to confirm the unequivocal existence of the disorder. A category
of the International Classification of Sleep Disorders. |
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