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Active Sleep:

Stage of sleep in neonates and infants equivalent to REM sleep in adults.

Advanced Sleep Phase Syndrome:

A disorder in which the major sleep episode is advanced in relation to the desired clock-time, that results in symptoms of compelling evening sleepiness, and early sleep onset, and an awakening that is earlier than desired.

Alpha Activity:

EEG waveform activity in the 8-13 Hz (cycle per second) range. Considered as the "wake" state.

Alpha Intrusion:

Alpha waves over-riding/super-imposing/superceding on all other sleep stages.

Alpha Rhythm:

EEG waveform in the 8-13 Hz range. Considered as the "wake" state. Seen predominantly in the occipital regions (01 and )2).

Alpha Sleep:

The "waking" state.

Alpha-Delta Sleep:

Alpha waves over-riding/super-imposing/superceding on delta (AKA: slow waves) sleep.

Apnea:

Cessation of nasal/oral airflow lasting at least 10 seconds in duration (in adults).

Apnea-Hypopnea Index:

The total number of apneas and hypopneas per hour of sleep.

Apnea Index:

The total number of apneic episodes (obstructive, mixed, central) per hour of sleep.

Apnea of Infancy (AOI):

Infants < 37 weeks gestation at the onset of the apnea and for whom no specific cause of ALTE or apnea can be identified.

Apnea of Prematurity:

Infants < 37 weeks gestation; not due to an explainable cause except respiratory immaturity.

Apparent Life Threatening Event (ALTE):

A clinical syndrome and may be associated with an unexplained apnea or an apnea of known cause.

Arousal:

A brief interruption in sleep of at least 3 seconds duration; may or may not cause a stage change.

Atonic:

Without normal muscle tone.

Beta Activity:

EEG waveform with a frequency > 13 Hz (cycles per second); may be drug-induced.

Bruxism:

Grinding or clenching of the teeth during sleep.

Capnograph

Detects increased CO2 in expired air (indirect).

Cataplexy:

Sudden loss of muscle tone; usually associated with a strong emotional stimulus. Appears to be a sudden onset of REM-related muscle atonia but without loss of consciousness.

Cheyne-Stokes Respiration:

Breathing pattern characterized by regular "crescendo-decrescendo-central event" fluctuations in respiratory rate and tidal volume.

Circadian Rhythm:

Daily fluctuation of physiological or behavioral functions, including sleep-wake states generally tied to the 24-hour daily dark-light cycle, but sometimes at a measurably different periodicity when light-dark and other time cues are removed.

Cycles Per Second (cps):

Number of "peaks" (EEG waves) occurring in a one second time-frame.

Deep Sleep:

AKA Stages 3 and 4 sleep, Slow Wave Sleep, restorative sleep; Delta Sleep.

Delayed Sleep Phase Syndrome:

A condition where one's internal clock is moved back (delayed) in a given 24-hour sleep-wake cycle.

Delta Activity:

EEG waveform with a frequency of 0.5-2 Hz (cps) with an amplitude of at least 75 µV from peak to peak in at least 20% of the epoch.

Delta Sleep:

Stage in which a person is in Stage 3 or 4 sleep. AKA: Slow Wave Sleep.

Differential AC Amplifiers:

Used to record physiologic parameters of high frequency such as EEG, EOG, EMG and ECG. AC amplifiers have both high and low frequency filters.

Direct Current (DC) Amplifiers:

Do not have a low frequency filter; used to record slower-moving potentials such as output from the oximeter, pH meter, CPAP pressure.

Diurnal:

Happening in the daytime.

Drowsiness:

State of subtle wakefulness prior to sleep onset.

Dyssomnia:

A primary disorder of initiating or maintaining sleep (or wakefulness).

Electroencephalogram (EEG):

A recording of electrical activity of the brain by means of electrodes placed on the surface of the head. Used to score the stages of sleep.

Electromyogram (EMG):

A recording of electrical activity from the muscular system by means of surface electrodes placed in designated areas during sleep (i.e., chin, mentalis, submentalis, masseter, anterior tibialis, intercostals, extensor digitorum).

Electro-oculogram (EOG):

A recording of voltage changes resulting from shifts in position of the ocular globes by means of electrodes placed near the eyes to record the movement of the eyes.

Enuresis:

Bed-wetting that occurs typically during Slow Wave Sleep.

Epoch:

Corresponds to a page of the polysomnogram. Typically an epoch is 30 seconds in duration (based on a paper speed of 10 mm/sec).

Excessive Daytime Somnolence (EDS):

A subjective report of maintaining wakefulness and a rapid initiation into sleep when the individual is sedentary. Most commonly occurs during the daytime, however excessive sleepiness may be present at night when an individual's major sleep period is during the daytime (i.e., shift worker).

FIO2:

Fraction of O2 in inspired air.

First Night Effect:

Reduced quality compared to that which would be expected in the subjects usual sleeping environment without recording equipment. Habituation to the laboratory setting is found by the second night of recording.

Fuctional Residual Capacity:

End of normal expiration where much more air remains in the lungs.

Hertz (Hz):

A unit of frequency; preferred term to the synonym: cycles per second.

High Frequency Filter (HFF):

Used to attenuate the amplitude of faster frequency activity. Affects the frequency of the filter setting and higher. AKA: Low pass filter.

Hypercapnia:

Elevated carbon dioxide level in the blood.

Hypersomnia:

Excessive sleepiness: deep or prolonged major sleep period. May be associated with difficulty awakening, or sleep drunkenness.

Hypnic Jerk:

A "sleep start" or sudden body jerk; occurring generally at sleep onset; usually occurring in a brief awakening. AKA: Hypnic startle.

Hypnogogic:

Occurrence of an event during the transition from wakefulness to sleep.

Hypnopompic:

Occurrence of an event during the transition from sleep to wakefulness.

Hypopnea:

An episode of shallow breathing (diminished airflow) during sleep; lasting ≥ 10 seconds; usually associated with a fall in blood oxygen saturation value and/or associated with an arousal.

Insomnia:

Difficulty in initiating and/or maintaining sleep.

Jactatio Capitus Nocturna:

A rhythmic disorder; comprised of a group of sterotyped repetitive movements; usually of the head and neck; which typically occur immediately prior to sleep onset and are sustained into light sleep. AKA: Head-banging or Body-Rocking.

K-Complex:

A sharp, bi-phasic EEG wave followed by a high voltage slow wave. The complex duration is at least 0.5 seconds and may be accompanied by a sleep spindle.

Klein-Levin Syndrome:

Recurrent episodes of hypersomnia and bulimia that typically occurs weeks or months apart; associated with voracious eating or hypersexuality. During the sleep "attacks", patients sleep 16-18 hours a day or more, and on awakening they eat voraciously. Behavioral disturbances could include: dull appearance, withdrawal, confusion, hallucinations, memory impairment, and hypersexuality.

Low Frequency Filter (LFF):

Attenuates the amplitude of slower frequency activity. Affects the frequency of the filter setting and lower. AKA: High pass filter.

Maintenance of Wakefulness Test (MWT):

A series of measurements to assess wakefulness in a darkened room while in a semi-reclined position. Long latencies to sleep are indicative of the ability to remain awake. Most useful for assessing the effects of medications upon the ability to remain awake.

Montage:

The particular arrangement by which a number of derivations are displayed simultaneously on a polysomnogram.

Movement Arousal (MA):

A body movement associated with an EEG pattern of arousal or a full awakening; a sleep scoring variable.

Movement Time (MT):

EEG and EOG tracings are obscured for more than half the scoring epoch because of movement. The preceding OR succeeding epoch must be sleep.

Multiple Sleep Latency Test (MSLT):

A series of measurements whereby subjects are allowed a fixed number of opportunities to fall asleep during their customary wake period. Excessive sleepiness is characterized by short latencies. Long latencies are helpful in distinguishing physical tiredness or fatigue from true sleepiness.

Munchausen Syndrome by Proxy:

A child is reported to have medically serious symptoms, which, in fact, are induced by an adult; usually a caregiver or parent.

Nightmare:

A term used to denote an unpleasant and frightening dream that occurs in REM sleep. AKA: dream anxiety attack.

Night Terror:

AKA: Pavor Norturnus; occurs during Delta or Slow Wave Sleep. Characterized by an increase in heart rate and respiratory rate followed by activity (i.e., screaming) out of Slow Wave Sleep; generally occurs during the first third of the night.

Nocturnal Penile Tumescence (NPT):

see Sleep Related Erections (SREs)

Paradoxical Sleep:

Synonymous with REM sleep; the preferred term.

Parasomnia:

Disorder of arousal, partial arousal, or sleep stage transition.

Periodic Limb Movements in Sleep (PLMS):

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 movement occur with a periodicity of 20-40 seconds in a pattern lasting 0.5-5 seconds in duration. AKA: Periodic Movements in Sleep (PMS).

PLMS Arousal Index:

The number of sleep-related periodic limb movements per hour of sleep that are associated with an EEG arousal.

PLMS Index:

The number of periodic limb movements per hour of total sleep time.

PCO2:

Pressure of carbon dioxide.

PGO Spikes:

Ponto-Geniculo-Occipital spikes are the essence of REM sleep; typically associated with the phasic events during REM but associated with dreams and their unpredictability.

PO2:

Pressure of Oxygen.

Polysomnogram (PSG):

The continuous and simultaneous recording of physiological variables during sleep (EEG, EOG, EMG - the three basic stage scoring parameters), EKG, respiratory airflow, respiratory movements, limb movements, and other electrophysiological variables.

Ptosis:

Drooping eye-lids.

Quiet Sleep:

Term used for describing non-REM sleep in infants and animals when specific NREM sleep stages 1-4 cannot be determined.

REM Density:

A function that expresses the frequency of eye movements per unit time during stage REM.

REM Sleep Latency:

The interval from sleep onset to the first appearance of stage REM sleep in the sleep episode.

REM Rebound (Recovery):

Lengthening and increase in frequency and density of REM sleep episodes which result in an increase in REM-sleep percent above baseline. REM-sleep rebound follows REM-sleep deprivation once the depriving influence is removed.

Respiratory Disturbance Index (RDI):

The number of apneas (obstructive, mixed, central) hypopneas and RERAs per hour of total sleep time.

Sawtooth Waves:

A form of theta rhythm that occurs during REM sleep and is characterized by a notched appearance in the waveform. Occurs in bursts lasting up to 10 seconds in duration.

Sixty Hertz (60 Hz) Notch Filter:

Eliminates frequencies between 58-62 cps and attenuates activity close to Hz. Designed to filter out electrical interference.

Sleep Efficiency:

Proportion of sleep in the episode potentially filled by sleep. The ratio of Total Sleep Time to Time in Bed.

Sleep Latency:

The duration of time measured from "lights out" or bedtime to the onset of sleep.

Sleep Onset:

The transition from wake to sleep. Defined as 15 seconds or more of any stage of sleep on an epoch.

Sleep Onset REM Period (SOREMP):

The beginning of sleep by entrance directly into stage REM sleep. The onset of REM sleep occurs within 10 minutes of sleep onset.

Sleep Paralysis:

Immobility of the body that occurs in the transition from sleep to wakefulness which is a partial manifestation of REM sleep.

Sleep Related Erections (SREs):

The natural periodic cycle of penile erections that occur during sleep; typically associated with REM sleep. Consists of four phases: T-up (ascending tumescence), T-max (plateau; maximal tumescence), T-down (de-tumescence), and T-zero (no tumescence). Preferred term over NPT.

Sleep-talking (Somniloquy):

Talking in sleep that usually occurs during stage REM; at which time it represents a motor break-through of dream speech. Can occur in the course of transitory arousals from NREM sleep.

Sleep-wake Cycle:

The clock hour relationships of the major sleep and wake episodes in the 24-hour cycle.

Sleep-walking (Somnambulism):

Occurring during Slow Wave/Delta sleep. Generally occurs during the first third of the night.

Sonogram:

Device used to pick up sounds related to snoring.

Time Constant:

The time it takes for a square wave to decay to 37% (or one-third) of its initial amplitude.

Total Recording Time (TRT):

The duration of time from sleep onset to final awakening. in addition to total sleep time, it is comprised of the time taken up by wake periods and movement time until wake-up. AKA: Time in Bed.

Total Sleep Time (TST):

The amount of actual sleep time in a recording period equal to total recording time less total wake time. Total sleep time equals total REM and NREM sleep in a sleep episode.

Tracé Alternant:

EEG pattern of newborns; characterized by bursts of slow waves; at times intermixed with sharp waves and intervening periods of relative quiescence with extreme low amplitude activity.

Zeitgebers:

An environmental time cue that usually helps entrainment to the 24-hour day, such as sunlight, noise, social interaction; alarm clocks.