Glossary of Terms

Terms used in sleep medicine:

Actigraph
A biomedical instrument used to measure body movement.

Active Sleep
Equivalent to REM sleep used in ontogenetic and phylogenetic literature.

Alpha Wave
EEG frequency of 8-12 Hz.

Alpha-Delta Sleep
Alpha wave occurring in Slow Wave Sleep.

Alpha Intrusion
A brief superimposition of alpha wave in various sleep stages.

Alpha Rhythm
EEG frequency of 8-12 Hz predominantly found in Occipital cortex during relaxed wakefulness with eyes closed.

Apnea
Cessation of oro-nasal airflow for 10 seconds or more during any sleep stage.

Apnea-Hypopnea Index
Number of apneic events per hour of sleep.

Arousal
Abrupt change of EEG frequency for at least 3 seconds occurring in any sleep stage.

Awakening
More than 15 seconds of wakefulness during any epoch of sleep stage.

Arousal Disorder
Type of parasomnia involving abnormal arousal mechanism from sleep.

Baseline
Typical or normal state of an investigative variable before experimental manipulation.

Bedtime
Clock time when one attempts to fall asleep, as differentiated from clock time when one gets into bed.

Beta Activity
EEG activity greater than 13 cycles per second associated with alert wakefulness.

Bruxism
Teeth grinding during sleep.

Cataplexy
Sudden loss of skeletal muscle tone and deep tendon reflexes causing postural collapse usually seen in narcoleptic patients.

Cheyne Stokes Respiration
Breathing pattern characterized by regular waxing and waning of respiratory rate and tidal volume.

Circadian Rhythm
Internal biological clock of sleep wake functions generally tied to 24-hour dark-light cycle.

Conditioned Insomnia
Type of psychophysiological insomnia produced by the development, during an earlier experience of sleeplessness.

Cycle
Rhythmic fluctuation of one maximum or minimum to the next.

Deep or Delta Sleep
Common term for stage 3 and 4 sleep.

Delayed Sleep Phase
A circadian rhythm sleep disorder delaying normal sleep wake cycle.

Delta Activity
EEG wave of .5 to 2 cycles per second, .5 second in duration and greater than 75 microvolt amplitude.

Desaturation:
Commonly denotes arterial oxygen desaturation.

Diurnal
Pertaining to the daytime.

Dyssomnia
A primary disorder of initiating and maintaining sleep or of excessive sleepiness.

End-Tidal Carbon Dioxide
CO2 value determined at the nostrils by an infrared gas analyzer.

Entrainment
Synchronization of a biological rhythm by a forcing stimulus such as environmental time cue.

Epoch
A measure of duration of sleep recording that is typically of 20 or 30 seconds duration.

Excessive Daytime Sleepiness
Usually subjective report of excessive and uncontrollable sleepiness at inappropriate time.

Extrinsic Sleep Disorders
Sleep disorders either originates, develops or arises from outside of the body.

Final Awakening
Amount of wakefulness that occurs after the final wake-up time until lights on.

First Night Effect
Altered sleep physiological variables due to unfamiliar sleeping environment and recording apparatus, commonly found in subjects in a sleep laboratory on the first night.

Fragmented Sleep
Repeated arousals and/or awakenings causing interrupted sleep.

Free Running Condition
Natural endogenous biological rhythm when environmental time cues are removed.

Hertz
Unit of frequency denoting cycles per second.

Hypercapnia
Elevated carbon dioxide level in blood.

Hypersomnia
Synonym to excessive sleepiness.

Hypnogram
NREM-REM sleep stages and cycles forming the infrastructure of sleep plotted in the form of histogram

Hypnogogic Hallucination
Occurrence of hallucination during transition from wakefulness to sleep or sleep onset.

Hypnopompic Hallucination
Occurrence of hallucination during transition from sleep to wakefulness or sleep offset.

Hypopnea
Referred to 50% reduction of oro-nasal airflow for 10 seconds or more during sleep, usually associated with an arousal and/or oxygen desaturation.

Insomnia
Difficulty in initiating and/or maintaining sleep.

K-Alpha
A K-complex followed by several seconds of alpha rhythm; a type of micro arousal.

K Complex
A sharp, negative EEG wave followed by sharp positive wave, duration of at least .5 seconds and amplitude of 50 microvolts.

Light Sleep
Usually refereed to stage-1 sleep.

Major Sleep Episode
The longest sleep episode that occurs during habitual sleeping time.

Microsleep
An episode lasting up to 10 seconds during which external stimuli are not perceived.

Montage
Particular arrangement of sleep derivatives displayed simultaneously in polysomnogram.

Myoclonus
Muscle contractions in the form of abrupt jerks or twitches.

Nap
A short sleep episode occurring during habitual wakefulness.

Nocturnal Dyspnea
Respiratory distress during nighttime.

Paradoxical Sleep
Synonymous with REM sleep.

Parasomnia
Abnormal behaviors or activities occurring during sleep.

Paroxysm
Phenomenon of abrupt onset, attain maximum and termination suddenly.

Phasic REM
Brief and episodic eye movements during REM sleep.

Pickwickian
A term applies to an individual who snores and had alveolar hypoventilation syndrome.

Quite Sleep
Term used to describe NREM sleep in in infants.

REM Sleep Onset
Commencement of REM sleep.

REM Sleep Latency
Interval from sleep onset to REM sleep onset.

REM Rebound
Increased frequency, duration and percentage of REM sleep commonly seen after REM sleep deprivation and during CPAP titration.
Respiratory Disturbance Index: Number of all apneas and hypopneas per hour of total sleep time.

Saw Tooth Waves
Notched appearance of EEG waves of 3 to 7 cycles per second occurring during REM sleep.

Sleep Architecture
NREM-REM sleep stages and cycles forming the infrastructure of sleep, often plotted in the form of histogram.

Sleep Diary
A daily written record or log of a person’s sleep-wake pattern.

Sleep Cycle
Synonymous with NREM-REM cycle.

Sleep Efficiency
Proportion of total sleep time and time in bed.

Sleep Hygiene
Conditions and practices that promote continuous and effective sleep.

Sleep Latency
Duration of time from lights off to sleep onset.

Sleep Onset
Transition from wakefulness to sleep after lights off.

Sleep Mentation
Imaginary and thinking experienced during sleep.

Sleep Paralysis
Immobilty of body at sleep offset as a manifestation of REM sleep in narcoleptic patients.

Sleep Spindle
Spindle shaped EEG bursts of 12 to 14 cycles per second lasting .5 to 1.5 seconds and of 50 microvolt amplitude.

Somnumbulism
Type of parasomnia causing sleep walking.

Theta Activity
EEG wave of 3 to 7 cycles per second seen in stage-1 and REM sleep.

Total Sleep Time
Amount of MREM and REM sleep between lights off and lights on.

Trace Alternants
EEG pattern of sleeping newborn, characterized by bursts of slow waves, intermixed with sharp waves and intervening period of relative quite period of low-amplitude activity.

Tumescence (Penile)
Hardening and expansion of penis associated with REM sleep.

Vertex Wave
Sharp negative EEG wave of high amplitude usually occurring during stage-1 sleep.

Zeitgeber
Environmental time cue that usually helps to entrain biological clock.

Abbreviations used in sleep medicine: