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Sleep Apnea Definitions – R To Z

August 29th, 2009


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Sleep Apnea Definitions – R To Z

These are a list of common definitions from R to Z as used in discussions about Sleep Apnea.

Radiofrequency (RF) – Electromagnetic radiation in the frequency range 3 kilohertz (kHz) to 300 gigahertz (GHz); considered to include microwaves and radio waves.  Microwaves occupy the spectral region between 300 GHz and 300 MHz, while RF or radio waves include 300 MHz to 3 kHz.


Radiofrequency (RF) Procedure (also known as Somnoplasty) – procedure for treating nasal obstruction, snoring and in some cases, sleep apnea. The procedure uses radiowave energy to reduce snoring and the size of the soft palate.


RDI – Respiratory Disturbance Index, includes all respiratory events per hour.


REM sleep, rapid eye movement sleep – sleep characterized by the active brain waves, flitting motions of the eyes, and weakness of the muscles; most dreaming occurs in this stage, which accounts for about 20% of sleep in adults.


REM Density – A function that expresses the frequency of eye movements per unit of time during REM sleep.


REM-Associated Disorders – Sleep disturbances that occur in REM sleep.


REMS latency – The period of time in the sleep period from sleep onset to the first appearance of stage REMS.


REM Motor Atonia – The active suppression of activity in the antigravity and voluntary muscles during REM sleep. The muscles are completely flaccid and limp.


REM onset – designation for commencement of a REM period;  used also as a shorthand term for a sleep-onset REM period.


REM period – REM portion of a NREM-REM cycle; early in the night it may be as short as a half-minute, whereas in later cycles longer than an hour.


REM rebound or recovery – lengthening and increase in frequency and density of REM.

periods, which results in an increase in REM percent above base line. REM rebound follows REM deprivation once the inhibitory influence is removed.


REM Sleep Behavior Disorder (RBD)– disorder in which REM motor atonia is partially or completely absent and the individual acts out the ongoing dream. The behavior in REM behavior disorder is often correlates with the ongoing, hallucinatory REM dream episode.


REM Sleep Episode – REM sleep portion of a NREM-REM sleep cycle. Early in the first sleep period, episodes may be only several minutes in duration. Later REM episodes almost are always longer, 20 to 30 minutes up to an hour.


REM Sleep Intrusion – brief interval of REM sleep appearing out of its usual positioning in the NREM-REM sleep cycle.


REM Sleep Latency – interval from sleep onset to the first appearance of REM sleep.


REM Sleep Onset – designation for the first epoch of a REM sleep episode.


REM Sleep Percent – proportion of total sleep time occupied by REM sleep.


REM Sleep Rebound – compensatory increase in REM sleep following experimental reduction. Extension of time in, and an increase in frequency and density of REM sleep episodes;  usually an increase in REM sleep percent of total sleep time above baseline values.


Respiratory Care Practitioner (RCP) – licensed health care professional specifically trained in cardiopulmonary assessment, diagnostics, therapy administration, and patient education, including the identification and treatment of sleep disorders.


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;  the sensations are relieved by movement.


Restlessness (Referring to Quality of Sleep) – Persistent or recurrent body movements, arousals, and/or brief awakenings in the course of sleep.


Sedatives – compounds tending to calm, and reduce nervousness or excitement and foster sleep.


Sedentary Situation – not requiring physical activity, e.g. working at a desk, sitting in a meeting or in a theater, watching television.


Septoplasty – surgery on the nasal septum (dividing the nasal passage).


Serotonin – neurotransmitter in the brain that modulates mood, appetite, sexual activity, aggression, body temperature and sleep.


Shiftwork – working hours outside of the conventional daytime hours of 9:00 a.m. to 5:00 p.m.


Sleep – a state marked by lessened consciousness, lessened movement of the skeletal muscles, and slowed-down metabolism.


Sleep Apnea – cessation of breathing for 10 or more seconds during sleep.


Sleep architecture – NREM/REM stage and cycle infrastructure of sleep understood from the vantage point of the quantitative relationship of these components to each other.


Sleep cycle – synonymous with NREM-REM cycle.


Sleep Debt – result of recurrent sleep deprivation which occurs over time when an individual does not experience a sufficient amount of the restorative daily sleep that is required to maintain a sense of feeling rested and refreshed.


Sleep Deprivation – acute or chronic lack of sufficient sleep.


Sleep Disorders – broad range of illnesses arising from many causes, including, dysfunctional sleep mechanisms, abnormalities in physiological functions during sleep, abnormalities of the biological clock, and sleep disturbances that are induced by factors extrinsic to the sleep process.


Sleep efficiency (SE) – proportion of sleep in the period potentially filled by sleep–ratio of total sleep time to time in bed.


Sleep Episode – interval of sleep that may be voluntary or involuntary.


Sleep Extension – extending sleep time by increasing the time in bed.


Sleep Fragmentation – brief arousals occurring throughout the night, reducing the total amount of time spent in the deeper levels of sleep.


Sleep hygiene – conditions and practices that promote continuous and effective sleep, including regularity of bedtime and arise time; conforming time spent in bed to the time necessary for sustained and individually adequate sleep (i.e., the total sleep time sufficient to avoid sleepiness when awake);  restriction of alcohol and caffeine beverages in the period prior to bedtime;  employment of exercise, nutrition, and environmental factors so that they enhance, not disturb, restful sleep.


Sleep Hyperhydrosis – excessive sweating during sleep.


Sleep Inertia – feelings of grogginess and/or sleepiness that persist longer than 10 to 20 minutes after waking up.


Sleep interruption – breaks in the sleep architecture resulting in arousal and wakefulness.


Sleep latency – time period measured from “lights out,” or bedtime, to the beginning of sleep.


Sleep log (-diary) – daily, written record of an individual’s sleep-wake pattern containing such information as time of retiring and arising, time in bed, estimated total sleep period, number and duration of sleep interruptions, quality of sleep, daytime naps, use of medications or caffeine beverages, nature of waking activities, and other data.


Sleep-maintenance DIMS or insomnia – disturbance in maintaining sleep once achieved;  persistently interrupted sleep without difficulty falling asleep.


Sleep Mentation – thoughts, feelings, images, perceptions, hallucinations, and active dreams taking place during sleep.


Sleep onset – transition from wake to sleep, normally into NREM stage 1 (but in certain conditions, such as infancy and narcolepsy, into stage REMS).


Sleep Onset Imagery – images and experiences during the moments following the transition from wake to sleep.

Sleep-onset REM period – atypical beginning of sleep by entrance directly into stage REM.

Sleep paralysis – waking and not being able to move for a short period of time, usually occurs out of REM (dream) sleep.

Sleep pattern (24 hour sleep-wake pattern) – individual’s clock hour schedule of bedtimes and rise times as well as nap behavior: may also include time and duration of sleep interruptions.

Sleeping Pills – compounds that have a sedative effect,  used to produce sleepiness.

Sleep Related Accidents – accidents caused by individuals who were sleep deprived and who, as a result, had impaired judgment.

Sleep Restriction – limitation of the number of hours in bed.

Sleep spindle – episodically appearing, spindle-shaped aggregate of 12-14 Hz waves with a duration of 0.5-1.5 seconds, one of the identifying EEG phenomena of NREM stage 2 sleep
Sleep Stage Demarcation – significant polysomnographic characteristics that distinguish the boundaries of the sleep stages.

Sleep stage NREM –  major sleep state apart from REMS; comprises sleep stages 1-4
Sleep stage 1 – a stage of NREM sleep occurring after wake. Its criteria consist of a low-voltage EEG with slowing to theta frequencies, alpha activity less than 50%, EEG vertex spikes, and slow rolling eye movements; no sleep spindles, K-complexes, or REMS.  Stage 1 normally assumes 4-5% of total sleep.



Sleep stage 2 – a stage of NREM sleep characterized by sleep spindles and K complexes against a relatively low-voltage, mixed-frequency EEG background; high-voltage delta waves may comprise up to 20% of stage 2 epochs; usually accounts for 45-55% of total sleep time.


Sleep stage 3 – a stage of NREM sleep defined by at least 20 and not more than 50% of the period (30 second epoch) consisting of EEG waves less than 2 Hz and more than 75 uV (high -amplitude delta waves); a “delta” sleep stage; with stage 4, it constitutes “deep “NREM sleep;  appears usually only in the first third of the sleep period; usually comprises 4-6% of total sleep time.


Sleep stage 4 – all statements concerning NREM stage 3 apply to stage 4 except that high-voltage, slow EEG waves, cover 50% or more of the record;  NREM stage 4 usually 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 REM – the stage of sleep found in all mammal studies, including man, in which brain activity is extensive, brain metabolism is increased, and vivid hallucinatory imagery, or dreaming occurs (in humans).  Also called “paradoxical sleep” because, in the face of this intense excitation of the CNS and presence of spontaneous rapid eye movements, resting muscle activity is suppressed.  The EEG is a low-voltage, fast-frequency, non alpha record.  Stage REMS is usually 20-25% of total sleep time.


Sleep structure – similar to sleep architecture.  Sleep structure, in addition to encompassing sleep stage and cycle relationships, assesses the within-stage qualities of the EEG and other physiological attributes.


Sleepiness (somnolence, drowsiness) – difficulty in maintaining the wakeful state so that the individual falls asleep if not actively kept aroused;  not simply a feeling of physical tiredness or listlessness.


Sleep talking – talking in sleep takes place during stage REMS, representing a motor breakthrough of dream speech, or in the course of transitory arousals from NREMS and other stages.  Full consciousness is not achieved and no memory of the event remains.


Sleepwalker or Sleepwalking – individual subject to somnambulism (one who walks while sleeping).  Sleepwalking typically occurs in the first third of the night during deep NREM sleep (stages 3 and 4).


Sleep-wake, 24 hour cycle – the clock hour relationships of the major sleep and wake phases in the 24 hour cycle: similar to sleep pattern.


Sleep-wake shift (-change, -reversal) – sleep wholly or partially moved to a time of customary waking activity, and the latter is moved to the habitual sleep period; common in jet lag and shift work.


Sleep-Wake Transition Disorder – disorder occuring during the transition from wakefulness to sleep or from one sleep stage to another;  a form of parasomnia.


Slow wave sleep (SWS) – sleep stages 3 and 4.


SmartPAP (Smart CPAP) – (Smart Continuous Positive Airway Pressure) Medical device used in the treatment of obstructive sleep apnea providing preset levels of continuous airflow, and automatically adjusting to keep the breathing passages open by sensing changes in airway integrity. The air flows from the device through a tube that connects to a nose or face mask.


Snoring – noise produced primarily with inspiratory respiration during sleep owing to vibration of the soft palate and the pillars of the oropharyngeal inlet.  Many snorers have incomplete obstruction of the upper airway, and may develop obstructive sleep apnea.


Soft Palate – membranous and muscular fold suspended from the posterior margin of the hard palate and partially separating the oral cavity from the pharynx.


Somatic Complaints – awareness of pain or problems in the body.


Somnambulism – walking while asleep.


Somnifacient – inducing sleep; hypnotic, as in a drug.


Somnolence – prolonged drowsiness or sleepiness.


Somnoplasty – commercial name for radiofrequency treatment of certain sleep disorders


Soporific – causing or tending to cause sleep


Spindle REMS – condition in which sleep spindles persist atypically in REMS; seen in chronic DIMS conditions


Stanford Sleepiness Scale (SSS) – 7-point rating scale consisting of seven numbered statements describing subjective levels of sleepiness/alertness


Subjective Sleepiness – feelings of sleepiness


Substance Abuse – excessive use of alcohol or drug;  substances can cause sleep disturbances


Subwakefulness syndrome – syndrome defined as a defect in the CNS support system for waking.  The few individuals reported with subwakefulness syndrome have daytime drowsiness and daytime sleep episodes that are always composed of NREMS stages 1 or 2.  The naps occur repetitively.


Sudden Infant Death Syndrome (SIDS) –  sudden and unexpected death of an apparently healthy infant, whose death remains unexplained after the performance of an adequate postmortem investigation.  Death usually occurs during sleep.  SIDS is a classification that is used to describe a deceased infant. It is not a disease, nor can it be a diagnosis for a living baby.


Synchronization – chronobiological term used to indicate that two or more rhythms recur with the same phase relationship.  In an EEG tracing, the term is used to indicate an increased amplitude with an occasional decreased frequency of the dominant activities.


Synchrony – scheduling sleep to synchronize with the biological clock


Tachycardia – rapid heart rate, usually defined by a pulse rate of over 100 beats per minute (bpm).


Thermocouples – small devices placed near the nostrils or mouth to measure air flow by sensing temperature changes; expired air is warmer than inspired air.


Thermoregulation – regulation of body temperature in mammals.


Theta waves – EEG activity with a frequency of 4-8 Hz


Thoracic Excursion – thoracic (chest) movement, indicating respiratory effort.  Usually measured by the placement of a sensor band, which includes a strain gauge around the chest.  The sensor band records chest wall movement associated with respirations.


Tidal Volume –  amount of air that passes in and out of the lungs in an ordinary breath;  usually expressed in liters


Titration – progressive, stepwise increase in CPAP pressure applied during a polysomnogram to establish the optimal treatment pressure


Tolerance – in pharmacology, refers to the reduced responsiveness to a drug’s action as the result of previous continued and/or multiple exposure


Tonic (Event/Activity) – brain, muscle, or autonomic events, which are continuous.  Usually refers to continuous activity (e.g. muscle atonia) during REM sleep.


Tonsils – pair of prominent masses of lymphoid tissue that are located opposite each other in the throat between the anterior and posterior pillars of the fauces (the narrow passage from the mouth to the pharynx situated between the soft palate and the base of the tongue). Composed of lymph follicles grouped around one or more deep crypts.


Tonsillectomy – surgical removal of the tonsils


Total Recording Time – duration of time from sleep onset to final awakening. I n addition to total sleep time, it is comprised of the time taken up by wake periods and movement time until wake-up.


Total sleep period – period of time measured from sleep onset to final awakening. In addition to total sleep time, it is comprised of the time taken up by arousals and movement time until wake-up


Total sleep time (TST) – amount of actual sleep time in a sleep period; equal to total sleep period less movement and awake time.  Total sleep time is the total of all REMS and NREMS in a sleep period.


Tracheotomy – surgical procedure to create an opening in the trachea (windpipe) so that one can breathe


Tracheostomy – refers to the opening in the trachea. As a treatment for severe obstructive sleep apnea, a tube to assist oxygenation and ventilation and/or to overcome an obstruction in the airway located superiorly.


Transducer – device designed to convert energy from one form to another


Transient Arousals – brief awakenings from sleep


Transient Insomnia – difficulty sleeping for only a few nights


Tricyclic Antidepressants – medication for depression.  Most tricyclic antidepressants also reduce REM sleep;  also used to control cataplectic attacks, hypnogogic hallucinations, and sleep paralysis.


Tumescence (penile) – hardening and expansion of the penis: penile erection. Commonly referred to as nocturnal penile tumescence (NPT) in sleep recordings.


Turbinate – small, shelf-like, cartilaginous structures covered by mucous membranes, which protrude into the nasal airway to help warm, humidify, and cleanse inhaled air on its way to the lungs.


Twilight Zone – slang popular term to describe the waking state of individuals whose MSLT scores are 5 minutes or less. Such individuals are usually sleep deprived or suffer from a sleep disorder.


Twitch (Body Twitch) – very small body movement such as a local foot or finger jerk which is not usually associated with an arousal.


Unattended CPAP Titration Study – sleep study that is usually performed in the home, after determining that a patient has a sleep related breathing disorder such as OSA or Upper Airway Resistance Syndrome, and is likely to benefit from CPAP therapy.


Unintended Sleep Episode – sleep episode that is not planned and may happen during an activity in which such an episode is hazardous, such as when driving a car or working with machinery


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.


Upper Airway Resistance Syndrome (UARS) – part of the spectrum of obstructive sleep-related breathing disorders in which repetitive increases in resistance to airflow in the upper airway lead to brief arousals and daytime fatigue.  Apneas and hypopneas (see RDI) may be totally absent.  Blood oxygen levels can be in the normal range.


Uvula – small soft structure hanging from the bottom of the soft palate in the midline above the back of the tongue.


Uvulopalatopharyngoplasty (UPPP) – also abbreviated as UPP or UP3 this operation is performed on the throat to treat snoring and sleep apnea.  UPPP is an accepted means of surgical treatment has a curative rate of less than 50%.  Scientific evidence suggests that UPPP works best in retropalatal and combination retropalatal and retrolingual obstruction


Wake time – total time that is scored awake in a polysomnogram occurring between sleep onset and final wake-up


White Noise – mixture of sound waves extending over a wide frequency range that may be used to mask unwanted noise that may interfere with sleep


Wilkinson Addition Test – performance test;  numbers added for one hour. Often included in a battery of tests to measure the impact of acute or chronic sleep loss.


Withdrawal – effects experienced when a patient stops taking sleeping pills

Zeitgeber – environmental time cue that entrains biological rhythms to a specific periodicity.  Known Zeitgebers are light, melatonin and physical activity.  To be effective, these signals must occur when the biological clock is in a responsive phase.


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