This Glossary of Terms is intended for individuals unfamiliar to medical terminology.

Glossary of Terms

This Glossary of Terms is intended for individuals unfamiliar to medical terminology. Our goal is to provide better education and promote a better understanding of a person’s sleep disorder by using layman’s terms to define words that may be used by medical professionals to describe different sleep disorders.




A technology by Respironics that enhanced the sensation of breathing when using Auto-CPAP pressure.  Pressure assistance and relief is delivered on inhalation (as necessary) as well as exhalation to provide a more natural sensation of breathing while against an auto adjusting positive pressure.

Advanced Sleep Phase Syndrome (ASPS)

A sleep disorder that is diagnosed with patients who feel sleepy and go to bed early in the evening and wake up very early in the morning.


Cessation breathing for at least 10 seconds or longer.

Apnea Index (AI)

A measurement of the number of apneas per hour.

Apnea/Hypopnea Index (AHI)

A measurement of the number of apneas plus the hypopneas per hour.


A level 4 monitoring device that measures airflow, heart rate, and oxygen saturation.


To abruptly awaken from a deeper level of sleep.

Arousal Disorder

Parasomnia disorder presumed to be due to an abnormal arousal.  ie: sleepwalking, sleep terrors.


An irregular or absence of the heart rhythm.


A type of CPAP machine that changes pressures automatically to manage detected apneas and/or hypopneas.



Basic Sleep Cycle

The natural progression through the different sleep stages during sleep.


Urinating while asleep.


Medication intended for use to tranquilize and sedate.


Positive Pressure Therapy delivered through an inspiratory pressure and expiratory pressure.


Trademarked Bi-Level Therapy developed by Philips Respironics.

Body Position

The different positions identified during sleep to identify movement.


Heart rate lower than 60 beats per minute in an adult.

Brain Waves

Electrical activity studied by electroencephalography (EEG).


Teeth grinding while sleeping.




Technology developed by Respironics to enhance the sensation of breathing out against a standard CPAP pressure; it is a pressure relief system that works with your breathing to reduce the resistance upon exhalation.

C-Flex Plus

A New technology by Respironics that enhanced the sensation of breathing agains a standard CPAP pressure.  Pressure assistance and relief is delivered on inhalation (as necessary) as well as exhalation to provide a more natural sensation of breathing while against continuous positive pressure.

Cardiac Arrest

The sudden cessation of the heart.


Pertaining to blood vessels and the heart.


Sudden, dramatic decrement in muscle tone and loss of deep reflexes that leads to muscle weakness, paralysis, or postural collapse.  Usually caused by outburst of emotion:  laughter, startle, or sudden physical exercise; one of the symptoms associated to narcolepsy.

Central Apnea

The absence of breathing or Apnea caused by the failure of the respiratory centers of the brain.

Central Nervous System (CNS)

Brain and spinal cord.

Cheyne-Stokes Respiration (CSR)

A periodic breathing pattern observed with an increasing and decreasing in respiratory rate and tidal volume. Usually seen in patients with Congestive Heart Failure (CHF).


The treatment for circadian rhythm sleep disorder by changing sleeping and waking times to reset the biological clock.

Circadian Rhythms

The 24 hour day-night cycle associated with the daily fluctuation of behavioral and physiological functions, including sleep and waking.

Climatline Tube

This is the new climate regulating tubing developed by ResMed to reduce rainout on the tubing when requiring a higher humidity setting. The air temperature is regulated through the thermistor at the mask end of the tubing. This technology is an option on the S9 Elite and Autoset Models

Complex Sleep Apnea

A classification of sleep apnea characterized by the manifestation of central sleep apnea after the treatment of obstructive sleep apnea using positive pressure.


Adhering to or conforming to treatment such as CPAP therapy.

Continuous Positive Airway Pressure (CPAP)

A positive airway pressure device used to splint the airway open. The primary treatment option to manage obstructive sleep apnea.

CPAP Pressure

Positive pressure required to maintain an open airway in patients with sleep apnea using a CPAP machine. (units of measurement is in cmH2O).



Deep Sleep

Stages 3 and 4 identified during sleep studies via polysomnogram.

Delayed Sleep Phase

A sleep disorder that is diagnosed with patients who feel very sleepy and go to bed early in the morning (instead of the late evening) and wake up very late in the morning.

Delta Sleep

Sleep stages that refer to stages 3 and 4, respectively during a polysomnogram. (considered deep sleep)

Diagnostic Sleep Study

The monitoring of several physiological activities during sleep. ie: Polysomnogram, Overnight Oximetry, ApneaLink, Remmers Sleep Recorder.


A sleep disorder pertaining to frequent interruptions of wakefulness during sleep.



Electro-oculogram (EOG)

In sleep medicine, it is the method of measuring the eye movements to identify if an individual has rapid eye movement (REM sleep).

Electrocardiography (EKG)

A measurement of the electrical activity of the heart.

Electroencephalogram (EEG)

In sleep medicine, it is the method of measuring the electrical activity on the brain to identify the different stages of sleep.

Electromyogram (EMG)

In sleep medicine, it is the method of measuring the muscular activity usually to identify if an individual suffers from bruxism.

ENT Physician

A doctor specializing in Ear, Nose and Throat and normally perform surgical repair or reconstruction in these areas.


A period of time identified during sleep studies.

Epworth Sleepiness Scale

A series of questions to quantify an individuals tendency to feel sleepy during certain situations.

Excessive Daytime Sleepiness (EDS)

A subjective description of hypersomnolence in different situations.

Expiration (Expiratory Phase)

The part of the breathing cycle when one expels air from the lungs.

Expiratory Positive Airway Pressure (EPAP)

The pressure delivered upon expiration during Bi-level therapy



To feel tired.


A disease that is normally associated with chronic muscle pain and fatigue.

Flow Limitation

The partial closure and restriction of the upper airway to prevents effective flow of air into the lungs.



Gastroesphageal Reflux Disease (GERD)

Flow of stomach acid upwards into the esophagus that can cause arousals and can disrupt normal sleep.


Habitual Snorers

Individuals who snore nearly every night.

High Upper Airway Resistance Syndrome (HUARS)

A sleep-disordered breathing syndrome characterized by complaints of daytime fatigue and/or sleepiness, increased upper airway resistance during sleep, frequent arousals, and no significant drop in ones oxygen levels.


The addition of moisture to CPAP or BiPAP therapy to minimize dryness resulting from the constant airflow delivered during therapy.


A behavioral sleep disorder that results in a lack of quality sleep.


Elevated carbon dioxide in the blood.


Excessive sleepiness


High blood pressure

Hypnagogic Startle

A sudden jerking of the body observed normally when a person is about to fall asleep and results in momentary waking.


Fear of falling asleep.


Sleep-inducing medication


The lowest part of the pharynx that leads to the larynx and esophagus.


A reduction in air flow of 50% or greater often resulting in an oxygen desaturation.


Reduced rate and depth of breathing resulting a low movement of volume of air to the lungs.


Reduction of oxygen content in the blood.


Deficiency of oxygen delivered to the tissues of the body.




A symptom that describes difficulties falling asleep.

Inspiration (Inspiratory Phase)

The part of the breathing cycle when one takes in air.

Inspiratory Positive Airway Pressure (IPAP)

The pressure that is delivered upon inspiration during Bi-level or BiPAP therapy


A medical procedure that involves penetrating the skin or a body cavity.



Jet Lag

Interruption in the sleep pattern resulting from a major rapid shift in sleep time during travel to a different time zone.





Laser Assisted Avulopalatoplasty (LAUP)

Medical procedure describing a method of removing tissues within the upper airway.

Light Sleep

Stages 1 and 2 identified during sleep studies via polysomnogram.

Light Therapy

Treatment for SAD (Seasonal Affective Disorder) and other circadian rhythm disorders.

Limit-Setting Sleep Disorder

Sleep disorder due to child’s difficulty in falling asleep because of a chronic refusal go to bed.




Large tongue; usually present at birth.

Mandibular Advancment Device

Also known as an Oral Appliance; it is a treatment option for obstructive sleep apnea that requires a device that moves of the jaw to increase the size of the upper airway.


Describing the jaws and face.


Hormone secreted that helps maintain sleep; hormone of darkness.


Partial awakening from sleep.


Period during sleep that describes suddenly shifts from waking to sleep that lasts up to a few seconds.

Mixed Sleep Apnea

Sleep disordered breathing characterized by the presence of a central and obstructive apnea.

Motor Activity in Sleep

Muscular movement during sleep.

Motor Atonia

Absence of muscle activity during sleep.

Movement Arousal

Body movement associated with arousal or awakening.

Multiple Sleep Latency Test (MSLT)

An assessment of excessive daytime sleepiness and narcolepsy.

Muscle Tone

Amount of tension in a muscle.




A short period of planned sleep in the middle of the day.


Sleep disorder characterized by excessive sleepiness, cataplexy, sleep paralysis, hallucinations, and the abrupt transition from wakefulness into REM sleep.

Nasal Airflow/ Nasal Ventilation

Measuring inspiratory and expiratory airflow.


Frightening dreams occurring in REM sleep.

Nocturnal Sleep-Related Eating Disorder

Sleep walking accompanied by eating.


Medical procedure not involves penetrating the skin or a body cavity.

Non-REM or NREM sleep

Approximately 80% of sleep pertaining to stages 1 to 4.

NREM Sleep Intrusion

Brief period of NREM sleep patterns appearing in REM sleep.



Obesity-Hypoventilation Syndrome

Term applied to obese individuals having difficulty moving the appropriate volume of air to the lungs during sleep and wakefulness.

Obstructive Sleep Apnea

Cessation of airflow at least 10 seconds in the presence of continued inspiratory effort due to a physical obstruction of the upper airway.

Optimum Sleep

The ideal amount of sleep needed every night by an individual.


A device that measure the saturation of oxygen in the blood.

Oxygen Desaturation Index (ODI)

The number of events the oxygen content of the blood is reduced 4% or more per hour.




An event happening during sleep such as sleep walking.

Pathological Sleep

Abnormal sleep patterns.

Periodic Breathing

Repetitive pattern of breathing characterized by apneic pauses such as in Cheyne Stokes Respiration.

Periodic Limb Movement Disorder

Also known as periodic leg movements syndrome. A disorder characterized by periodic episodes of repetitive limb movements occuring during sleep that cause arousal in sleep.

Persistent Insomnia

Recurring insomnia that responds poorly to treatment.

Phase Advance

The process of shifting an individuals sleep time earlier in a 24-hour.

Phase Delay

The process of shifting an individuals sleep time later in a 24-hour.

Pickwickian Syndrome

A condition characterized by obesity, hypersomnolence, lethargy, chronic hypoventilation, hypoxia, and usually obstructive sleep apnea.

Pineal Gland

A gland in the brain secreting the hormone melatonin and serotonin.

PLMD-Arousal Index

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

Polysomnogram (PSG)

The “gold standard” for evaluating sleep disorders conducting in a sleep laboratory.

Post-Prandial Drowsiness

Sleepiness that occurs after a meal, usually lunch.

Prescribed CPAP Pressure

Physician prescribed pressure or settings determined by a CPAP titration sleep study that effectively manages a persons obstructive sleep apnea.





REM Disorders

Sleep disturbances that occur in REM sleep.

REM Motor Atonia

Muscle paralysis during REM sleep.

REM Sleep

Rapid eye movement sleep; sleep characterized by the active brain waves, eye movements and muscle paralysis; most dreaming occurs in this stage and accounts for about 20% of sleep in adults.

Respiratory Disturbance Index (RDI)

Pertains to all respiratory related events per hour measured via portable monitor or PSG.

Restless Legs Syndrome (RLS)

Sleep disorder characterized by a deep creeping, or crawling sensation in the legs that tends to occur when an individual is not moving. There is an almost irresistible urge to move the legs; these sensations are relieved by movement.


Persistent or recurrent body movements, arousals, and/or brief awakenings during of sleep.




Medication intended to calm an individual and may induce sleep.


Hormone that control mood and alertness.


Working hours outside of the conventional daytime hours of 9:00 AM to 5:00 PM.


A natural process that is characterized by reduced sensory and motor activity, total or partial unconsciousness, and inactivity of voluntary muscles.

Sleep Apnea

Cessation of breathing for 10 or more seconds during sleep.

Sleep Architecture

The scientific process of sleep that is composed of the different stages that include NREM and REM sleep.

Sleep Debt

The accumulated amount of lost sleep resulting from chronic sleep deprivation or insufficient sleep time.

Sleep Deprivation

Insufficient sleep time.

Sleep Disorders

Illnesses during sleep that result in poor sleep quality or dysfunctional sleep.

Sleep Efficiency

The proportion of sleep that is a measurement effective and restorative sleep.

Sleep Episode

The voluntary or involuntary time a person sleeps.

Sleep Extension

A voluntary extension of total sleep time by increasing the time one stays in bed.

Sleep Fragmentation

Brief arousals occurring throughout the night hat reduces the amount of time in deep sleep and overall sleep efficiency.

Sleep Histogram

A graph of the different sleep stage.

Sleep Hygiene

A set of guidelines intended to improve sleep quality.

Sleep Hyperhydrosis

Excessive sweating during sleep.

Sleep Inertia

Feelings of grogginess after an abrupt awakening from sleep.

Sleep Latency

Time period measured from bedtime to the beginning of actual sleep.

Sleep Log or Sleep Diary

A detailed documentation of sleep patterns and subjective feelings during the day that help evaluate a persons perceived sleep quality; often done for 2 weeks.

Sleep Maintenance Insomnia

Difficulty in maintaining sleep without problems falling asleep.

Sleep Onset

Transition from wake to sleep.

Sleep Paralysis

Not being able to move for a short period of time even if an individual is conscious and awake; may be a sign of narcolepsy.

Sleep Pattern

An individual’s sleep and wake tendencies over a 24 hour period.

Sleep Related Accidents

Accidents that result from excessive daytime sleepiness secondary to poor sleep quality.

Sleep Restriction

Limitation of the number of hours in bed.

Sleep Stage 1

A stage of NREM sleep occurring after wake; Stage 1 normally assumes 4-5% of total sleep.

Sleep Stage 2

A stage of NREM that accounts for 45-55% of total sleep time.

Sleep Stage 3

A stage of NREM sleep in the first third of the sleep period; usually comprises 4-6% of total sleep time.

Sleep Stage 4

A stage of NREM that takes up 12-15% of total sleep time.  Somnambulism, sleep terror, and sleep-related enuresis episodes generally start in stage 4 or during arousals from this stage.

Sleep stage NREM

Major sleep state apart from REMS; comprises sleep stages 1-4.

Sleep Stage REM

Rapid eye movement sleep; sleep characterized by the active brain waves, eye movements and muscle paralysis; most dreaming occurs in this stage; it is usually 20-25% of total sleep time.

Sleep Structure

Similar to sleep architecture.

Sleep talking (Somniloquy)

Is the act of speaking during sleep. It’s a type of parasomnia that is an abnormal behavior that takes place during sleep.

Sleep-Wake Transition Disorder

A type of parasomnia characterized by a disorder occurring during the transition from one sleep stage to another.

Sleeping Pills

Medications that is used to sedate an individual.

Sleepwalking (Somnambulism)

Is a type of parasomnia. Sleepwalkers arise from NREM sleep in a state of low consciousness and perform activities that are normally seen awake individuals.

Slow Wave Sleep / Delta Sleep

Sleep stages 3 and 4.

SmartPAP / Smart CPAP

Same as Auto-CPAP or APAP.


A common sleep disorder that is characterized by the obstruction of airflow by the walls of the nose and mouth that causes vibrations and the distinctive sound of snoring.

Soft Palate

The tissues at the rear of the oral cavity consisting of muscular fibers enclosed in a mucous membrane; it closes off the nasal cavity from the oral cavity during swallowing or sucking.


Walking while asleep.


Drowsiness or sleepiness.


Radiofrequency treatment of certain sleep disorders.

Stanford Sleepiness Scale (SSS)

Seven numbered statements describing subjective levels of sleepiness/alertness.

Subjective Sleepiness

Feelings of sleepiness.

Sudden Infant Death Syndrome (SIDS)

Sudden infant death syndrome (SIDS) is the unexpected, sudden death of a child under age 1 in which an autopsy does not show an explainable cause of death.


Chronobiological term used to indicate that two or more rhythms recur with the same phase relationshipSynchrony – scheduling sleep to synchronize with the biological clock.




A heart rate of over 100 beats per minute.

Tidal Volume

Volume of air that passes in and out of the lungs in an ordinary breath.


Progressive adjustment of CPAP pressure to achieve an optimum pressures setting to effectively manage a person’s obstructive sleep apnea.


Ability to respond or continue with the prescribed therapy.


Surgical removal of the tonsils.


A pair of prominent tissue that are located opposite each other in the throat.

Total Sleep Period

Period of time measured from sleep onset to final awakening.


Surgical procedure to create an opening in the trachea that bypasses the obstruction so that one can breathe.

Transient Arousals

Brief awakenings from sleep.

Transient Insomnia

Difficulty sleeping for only a few nights.

Tricyclic Antidepressants

Medication for depression.


A structure located in the nasal passages that direct air to the areas of the nose that control the climate of the air entering the body.


Very small jerking movements that is not usually associated with an arousal.



Unintended Sleep Episode

An unexpected sleep period that may result in a dangerous situation for an individual.

Upper Airway

Part of the respiratory anatomy that includes the nose, nostrils, sinus passages, septum, turbinates; the tongue, jaws, hard and soft palate, muscles of the tongue and throat, etc.


The small piece of soft tissue that can be seen dangling down from the soft palate over the back of the tongue.

Uvulopalatopharyngoplasty (UPPP)

A surgical procedure performed by an ENT specialist as a alternative treatment option to manage obstructive sleep option.





White Noise Generator

A device that produces a particular sound used to drown out unwanted sounds that may interrupt a persons sleep. Commonly used by people who suffer from Tinnitus.


The effects a person may experience after ceasing to take medications such sleep medication.