Definitions and Abbreviations:

Abdominal Movement - In diagnostic sleep studies, abdominal movement is recorded. This is one of the measures of respiratory effort, reflecting movement of the diaphragm.

Advanced Sleep Phase Syndrome (ASPS) - Phases of the daily sleep/wake cycle are advanced with respect to clock time. This is classified as a circadian rhythm disorder. The sleep phase occurs well ahead of the conventional bedtime and the tendency is to wake up too early.

Alpha rhythm - EEG oscillations, prominent over the occipital cortex, with a frequency of 8-13 Hz in adults; indicative of the awake state; present in most, but not all, normal individuals; most consistent and predominant during relaxed wakefulness.

Alpha intrusion - brief occurrence of alpha activity during a stage of sleep.

Ambulatory Monitor - Portable system used to record (continuously) multiple physiological variables during sleep.

Apnea - Literally means "no breath"; the cessation of airflow at the nostrils and mouth for at least 10 seconds.

Apnea index (AI) - A measure of the severity of sleep apnea; the number of apnea events per hour.

Apnea/Hypopnea index (AHI) - the number of apneas and hypopneas per hour. 5-20=mild, 21-50=moderate, above 51 severe

Arousal - abrupt change from sleep to wakefulness, or from a "deeper" stage of non-REM sleep to a "lighter" stage

Arousal Disorder - parasomnia disorder presumed to be due to an abnormal arousal function. Classical arousal disorders: sleepwalking, sleep terrors and confusional arousals.

Arousal Threshold - ease that a sleeping person is awakened.

Arrhythmia - irregularity or absence of the heart rhythm caused by disturbances in transmission of electrical impulses through cardiac tissue.

Auto Adjusting Continuous Positive Airway Pressure Device (SmartPAP) (Auto-PAP) - A type of CPAP machine monitoring changes in breathing and compensates automatically by making appropriate adjustments in pressure.

Automatism - automatic action--especially any action performed apparently without intention or awareness.

Basic Sleep Cycle - progression through orderly succession of sleep states and stages. For the healthy adult, the first cycle is begins by going from wakefulness to non-REM sleep. The first REM period follows the first period of non-REM sleep, and the two sleep states continue to alternate throughout the night with an average period of about 90 minutes. A night of normal human sleep usually consists of 4-6 non-REM/REM sleep cycles.

Benzodiazepines - developed in the 1950's, this class of compounds tranquilize and sedates.

Beta Activity - brain waves with a frequency of greater than 13 Hz (Hertz).

Bi-Level - Bi-level pressure device used to treat sleep apnea. The "bi" refers to two pressures: a lower pressure for exhalation and a higher pressure for inhalation. Bi-Level machines are more expensive than a standard CPAP, but some patients tolerate it better because they can exhale comfortably against the constant inhalation pressure. (Sometimes called Bi-PAP, but that is a trademark name of one system)

Biological Clock - term for the brain process causing us to have 24-hour fluctuations in body temperature, hormone secretion, and other bodily activities. The most important function fosters the daily alternation of sleep and wakefulness. The biological clock is found in a pair of tiny bilateral brain areas called the suprachiasmatic nuclei.

Body Position - four positions are identified which a patient may be sleeping; back, left side, right side or abdomen. The time spent sleeping in each position and the number of respiratory events in a particular position are tabulated.

Bradycardia - heart rhythm with a rate lower than 60 beats per minute in an adult.

Brain Waves - the brain's spontaneous electrical activity studied by electroencephalography (EEG).

Bruxism - teeth grinding during sleep

Cardiac Arrest - sudden cessation of the heart beat.

Cardiovascular - Pertaining to blood vessels and the heart

Cataplexy - 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 tetrad of symptoms of narcolepsy.

Central apnea - absence of airflow and inspiratory effort; apnea caused by irregularity in the brain's control of breathing. Central Nervous System (CNS) - brain and spinal cord.

Cheyne-Stokes respiration - breathing pattern typified by regular "crescendo-decrescendo" or waxing and waning fluctuations in respiratory rate and tidal volume.

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

Circadian rhythm - innate, daily, fluctuation of behavioral and physiological functions, including sleep waking, generally tied to the 24 hour day-night cycle but sometimes to a different (e.g., 23 or 25 hour) periodicity when light/dark and other time cues are removed.

Compliance - adhering to or conforming with a regimen of treatment such as CPAP

CPAP - Continuous Positive Airway Pressure; the device used to treat sleep apnea by sending positive airway pressure at a constant, continuous pressure to help keep an open airway, allowing the patient to breathe normally through his/her nose and airway

CPAP Pressure - pressure needed to maintain an open airway in a sleep apnea patient treated with CPAP, expressed in centimeters of water (cm H20). The positive pressure can range from 5 - 20 cm H20. Different patients require different pressures. The value is determined in a CPAP titration study.

Deep Sleep - refers to combined non-REM sleep stages 3 and 4 in sleep studies

Delayed sleep phase - A condition occurring when the clock hour at which sleep normally occurs is moved back in time in a given, 24 hour sleep-wake cycle. The result is a temporarily displaced (delayed) occurrence of sleep within the 24 hour cycle.

Delta sleep - stage(s) of sleep in which EEG delta waves are prevalent or predominant (sleep stages 3 and 4, respectively).

Delta waves - EEG activity with a frequency less than 4 Hz. In human sleep stage scoring, conventionally the minimum criteria for scoring delta waves is 75 uV (peak-to-peak) amplitude, and 0.5 second duration (2 Hz).

Diagnostic Sleep Study - monitoring of several physiological activities in a sleeping individual. Usually performed to determine the absence or presence of a specific sleep disorder. The sleep study can occur in a sleep disorders center or in a patient's home with portable recording equipment.

Diaphragm - large, concave muscle attached to the rib cage at bottom of the chest (top of the abdomen). Inhalation occurs when diaphragm contracts. Exhalation is passive as the muscle relaxes.

Diurnal - active and wakeful in the daytime versus active in the nighttime

DME - Durable Medical Equipment. Equipment such as wheelchairs and walkers which are prescribed for use by or on the order of a physician, also includes CPAP and BI-Level machines.

Drowsiness, Drowsy - quiet wakefulness occurring prior to sleep onset.

Dyssomnia - a disorder of sleep or wakefulness; not a parasomnia

Electrocardiography (EKG) - a method of measuring the electrical activity of the heart.

Electrodes - small devices transmitting biological electrical activity from subject to polygraph

Electroencephalogram (EEG) - recording through the scalp of electrical potentials from the brain and the changes in these potentials. The EEG is one of the three basic variables (along with the EOG & EMG) used to score sleep stages and waking. Surface electrodes are used to record sleep in humans, recording potential differences between brain regions and a neutral reference point, or between brain regions.

Electromyogram (EMG) - recording of electrical activity from the muscular system; in sleep recording, synonymous with resting muscle activity or potential. The chin EMG, along with EEG and EOG, is one of the three basic variables used to score sleep stages and waking. Surface electrodes are used to record sleep in humans, measuring activity from the submental or masseter muscles. These reflect the changes in resting muscle activity. During REM sleep the chin/cheek EMG is tonically inhibited.

Electro-oculogram (EOG) - recording of voltage changes resulting from shifts in position of the eyeball-possible because each globe is a positive (anterior) and negative (posterior) dipole; along with the EEG and the EMG, one of the three basic variables used to score sleep stages and waking. Human sleep recordings utilize surface electrodes placed near the eyes to record the movement of the eyeballs. Rapid eye movements in sleep indicate a certain stage of sleep ( usually REM sleep).

ENT - Ear, Nose and Throat. A doctor specializing in diseases of the Ear, Nose and Throat. These specialists often do surgery as well, and may be referred to as an ENT surgeon.

EPAP - Expiratory Positive Airway Pressure. Pressure prescribed for the expiratory (breathing out) phase of an individual on Bi-level CPAP therapy for OSA (obstructive sleep apnea).

Epidemiology - Scientific discipline studying the incidence, distribution, and control of disease in a population. Includes the study of factors affecting the progress of an illness, and, in the case of many chronic diseases, their natural history.

Epoch - A standard 30 second duration of the sleep recording that is assigned a sleep stage designation; for special purposes, occasionally longer or shorter epochs are scored.

Epworth Sleepiness Scale - index of sleep propensity during the day as perceived by patients, and derived from the answers to 8 questions.

Esophageal Pressure - measurement used to determine respiratory effort and by inference, airway resistance. Considered an invasive measure, generally used only in polysomnographic testing, conducted in sleep disorders centers.

Excessive daytime sleepiness or somnolence (EDS) - subjective report of difficulty in staying awake, accompanied by a ready entrance into sleep when the individual is sedentary

Expiratory Phase - air is expelled during this phase of the breathing cycle

Fatigue - feeling of tiredness or weariness usually associated with performance decrements

Fiberoptic Nasopharyngoscope - flexible fiberoptic scope used in the examination of nasal passages, pharynx, hypopharynx and larynx. Fibromyalgia - a disease syndrome whose primary symptoms are muscle pain and fatigue.

Flattening Index - number indicating the amount of airflow limitation caused by partial closure of the upper airway. 0.3 indicates an open airway, 0.15 is mildly obstructed, 0.1 is severely limited airflow, and 0.0 reflects a totally closed airway. Flattening Index is used to identify the condition known as Upper Airway Resistance Syndrome (UARS), and is continuously recorded in both diagnostic sleep studies and CPAP titrations.

Flow Limitation - the partial closure of the upper airway impeding the flow of air into the lungs.

Forbidden Zone - the period of strongest clock-dependent alerting, usually in the evening. Prevents falling asleep.

Fragmentation (pertaining to Sleep Architecture) - interruption of a sleep stage as a result of the appearance of a lighter stage, or to the occurrence of wakefulness, which leads to disrupted non-REM-REM sleep cycles.

GABA (Gamma-Amniobutyric Acid) - major neurotransmitter in the brain, which is considered to be involved in muscle relaxation, sleep, diminished emotional reaction and sedation.

Gastroesphageal Reflux Disease (GERD) - flow of stomach acid upwards into the esophagus that can cause arousals and disrupt sleep.

Genioglossus tongue advancement - a possible surgical treatment used for sleep apnea and/or snoring, improving the airway behind the base of the tongue. The genioglossus, the main tongue muscle, relaxes during sleep, often allowing the tongue to fall into the airway. The muscle attaches to the middle of the lower jaw. A segment of bone containing this muscle is pulled forward and stabilized, opening the airway space behind the tongue.

Habitual Snorers - those who snore nearly every night

Heart Rate or beats per minute (bpm) - pace/speed of the heart measured in beats per minute. 60-80 is considered normal in adults.

Hertz (Hz) - unit of frequency; equal to cycles per second (cps).

Histogram (sleep) - graph indicating sleep stages though out the night.

Humidification - moisture is added to the airflow as an adjunct to CPAP (Continuous Positive Airway Pressure) therapy in treating obstructive sleep apnea (OSA). Humidification can be added to the CPAP by diverting the airflow over or through a cool or heated water reservoir (humidifier) to prevent the upper airway from drying out.

Hyoid Suspension - a possible surgical procedure sometimes used in the treatment of sleep apnea and/or snoring, designed to improve the airway behind the base of the tongue. The hyoid bone is located in the neck where some tongue muscles attach. The hyoid bone is pulled forward in front of the voice box and can open the airway space behind the tongue.

Hyperactivity - typical behavior in a child with a sleep disorder which is causing lack of quality sleep

Hypercapnia - excessive or elevated carbon dioxide in the blood

Hyperirritability - Extreme irritability; seen in sleep deprived subjects.

Hypersomnia - excessive, prolonged sleep

Hypertension - High blood pressure.

Hypnagogic imagery (hallucinations) - Vivid sensory images occurring at sleep onset but particularly vivid with sleep-onset REM periods; feature of narcoleptic REM naps.

Hypnagogic startle - "sleep start" or sudden body jerk, observed normally just at sleep onset, resulting in at least momentary awakening

Hypnophobia - Morbid fear of falling asleep.

Hypnotics - Sleep-inducing drugs.

Hypopharynx - lowermost portion of the pharynx leading to the larynx and esophagus.

Hypopnea - shallow breathing in which the air flow in and out of the airway is less than half of normal--usually associated with oxygen desaturation.

Hypoventilation - reduced rate and depth of breathing.

Hypoxemia - abnormal lack of oxygen in the blood in the arteries.

Hypoxia - deficiency of oxygen reaching the tissues of the body.

Imidazopyridines - New class of compounds inducing sleepiness. (Zolpidem, trade name Ambien, is in this class).

Inappropriate Sleep Episodes - unplanned sleep periods often occuring in an unsafe situation (i.e., while driving). These episodes are always due to sleep deprivation.

Insomnia - complaint describing difficulty in sleeping

Inspiratory Phase - part of the breathing cycle in which air is inhaled.

Invasive - referring to a medical procedure in which a bodily orifice or the skin must be penetrated for the purpose of collecting data, or for diagnosing or treating a disorder

IPAP - Inspiratory Positive Airway Pressure. Physician prescribed pressure for the inspiratory phase on a Bi-level CPAP device, used in the treatment of OSA.

Jet Lag - disturbance induced by a major rapid shift in environmental time during travel to a new time zone

K-Alpha - type of microarousal; K complex followed by several seconds of alpha rhythm.

K complex - sharp, negative, high-voltage EEG wave, followed by a slower, positive component. K complex, occurring spontaneously during NREM sleep, beginning in (and defining) stage 2. K complexes can be elicited during sleep by external (particularly auditory) stimuli as well.

Laser assisted uvulopalatoplasty (LAUP) - can eliminate or decrease snoring but has not been shown to be effective in the treatment of sleep apnea.

Leg Movement - Leg movements are recorded in both diagnostic sleep studies and titration studies.

Letter of Medical Necessity (LMN) - certification by a physician that the prescribed item(s) is/are medically indicated, reasonable and necessary with reference to the standards of medical practice and treatment of a patient's condition

Light-Dark Cycle - periodic pattern of light (artificial or natural) alternating with darkness

Light Sleep - term used to describe non-REM sleep stage 1, and sometimes, stage 2.

Light Therapy - used in the treatment of SAD (Seasonal Affective Disorder) and other conditions. Exposes the eyes to light of appropriate intensity and duration and at the appropriate time of day to effect the timing, duration and quality of sleep.

Limit-Setting Sleep Disorder - disorder due to child's difficulty in falling asleep by delaying and refusing to go to bed

Linear Sleepiness Rating Scale - measure of subjective sleepiness. The scale contains a horizontal line, 100 mm in length--the right extreme is labeled "Very Sleepy" and the left extreme is labeled "Very Wide Awake."

Macroglossia - large tongue; usually a congenital disorder (present at birth)

Maxillofacial - pertaining to the jaws and face.

Mandibular Maxillary Osteotomy and Advancement (MMOA) - procedure developed for patients with retrolingual obstruction, patients with retropalatal and retrolingual obstruction who have not responded to CPAP and uvulopalatopharyngoplasty (UPPP).

Melatonin - hormone secreted by the brain's pineal gland

Micro-arousal - partial awakening from sleep

Micro-sleep - period lasting up to a few seconds during which the polysomnogram suddenly shifts from waking characteristics to sleep.

Mixed (sleep) apnea - interruption in breathing during sleep beginning as a central apnea then becoming an obstructive apnea.

Monocyclic - a single major sleep period and a single major wake period in a 24-hour day.

Motor Activity in Sleep - any muscular movement during sleep

Motor Atonia - the absence of muscle activity during sleep

Movement arousal - body movement associated with arousal or awakening; a sleep scoring variable.

Movement time - term used in sleep record scoring to denote when EEG and EOG tracings are obscured for more than 15 seconds due to movement.

Multiple sleep latency test (MSLT) - a series "nap tests" utilized in the assessment of excessive daytime sleepiness.

Muscle Tone - amount of tension in a muscle.

Myoclonus - muscle contractions in the form of "jerks" or twitches.

Nap - short period of planned sleep generally obtained at a time separate from the major sleep period.

Narcolepsy - sleep disorder characterized by excessive sleepiness, cataplexy, sleep paralysis, hypnogogic hallucinations, and an abnormal tendency to pass directly from wakefulness into REM sleep

Nasal Airflow/Nasal Ventilation - recording of the complete respiratory cycle by measuring inspiratory and expiratory airflow

National Commission on Sleep Disorders Research (NCSDR) - the commission (created by the U.S. Congress in 1990) conducted a comprehensive study of the social and economic impact of sleep disorders in America and made recommendations based on its findings to the Congress in January 1993

Neurology - branch of medicine that referring to the nervous system and its diseases

Neurotransmitters - endogenuous chemical components that are released from axon terminals of one neuron and transmit the signal to the next neuron by combining with its receptor molecules. Neurotransmitters important in the control of sleep and wakefulness include: norepinephrine, serotonin, acetylcholine, dopamine, adrenaline and histamine.

Nightmare - unpleasant and/or frightening dream occurring in REM sleep (different from a night terror)

Night Terrors - also known as sleep terrors, or pavor nocturnus. Night terrors are characterized by an incomplete arousal from slow wave sleep. If, the individual is awakened during a night terror, he/she is usually confused and does not remember details of the event. Night terrors are different from nightmares; if an individual is awakened during a nightmare, he/she functions well and may have some recall of the nightmare.

Nocturia - excessive, often frequent, urination during the night

Nocturnal - "Of the night;" pertaining to events happening during sleep or the hours of darkness.

Nocturnal Confusion - episodes of delirium and/or disorientation near or during nighttime sleep; often seen in victims of Alzheimers Disease and more common in the elderly

Nocturnal sleep - related eating disorder (NS-RED)- Getting up during the night and eating while sleepwalking. No recall in the morning.

Nocturnal Enuresis (Bedwetting) - urinating while asleep

Non-Invasive - Medical procedure not penetrating the skin or a body cavity.

NREM or non-REM sleep - characterized by slower and larger brain waves and little or no dream behavior; quiet sleep, slow-wave sleep; approximately 80% of sleep

NREM Sleep Intrusion - brief period of NREM sleep patterns appearing in REM sleep; a portion of NREM sleep not appearing in its usual sleep cycle position

Obesity-Hypoventilation Syndrome - term applied to obese individuals hypoventilating during wakefulness.

Obstructive apnea - cessation of airflow (at least 10 seconds) in the presence of continued inspiratory effort; cessation of breathing during sleep, due to a mechanical obstruction, such as a semi-collapsed trachea, tongue relaxed to back of the throat, or a large among of tissue in the uvula area.

Obstructive Hypopnea - periodic and partial closure of the throat during sleep resulting in reduced air exchange at the level of the mouth and/or nostril.

Ondine's Curse - the respiratory center in the brain is unable to stimulate breathing in response to an increased amount of carbon dioxide in the blood. Ondine's Curse or central alveolar hypoventilation typically worsens during sleep.

Optimum Sleep - average amount of sleep needed every night by an individual.

Oxygen Desaturation - less than normal amount of oxygen carried by hemoglobin in the blood; values below 90% are considered abnormal

Oxygen Saturation - measure of oxygen carried by hemoglobin in the blood. Normal values 90% - 100%.

Oximeter (Pulse) - gives estimates of arterial oxyhemoglobin saturation (SaO2) by utilizing selected wavelengths of light to non invasively determine the saturation of oxyhemoglobin (SpO2)

Oximetry (Pulse) - continuous monitoring of oxygen saturation of arterial blood from a pulse oximeter; the sensor is usually attached to the finger.

O2 - Chemical symbol for oxygen. Criterion lowest percent O2 saturation: Greater than 85%=mild, 80% to 85%=moderate, less than 80%=severe

Parasomnia - an event happening during sleep, or induced or exacerbated by sleep, such as sleepwalking or asthma; not a dyssomnia.

Paroxysmal nocturnal dyspnea (PND) - respiratory distress and shortness of breath due to pulmonary edema, appearing suddenly and often awakening the sleeping individual.

Pathological Sleep - abnormal sleep patterns.

Pavor Nocturnus (Night Terrors) - See Night Terrors.

Perceptual Disengagement - change in consciousness at the onset of sleep when environmental stimuli are no longer perceived, and there is no longer any conscious, meaningful interaction with the environment.

Periodic Breathing - repetitive apneic pauses, common in premature infants.

Periodic Limb Movement Disorder - also known as periodic leg movements and nocturnal myoclonus. Characterized by periodic episodes of repetitive and highly stereotyped limb movements occuring during sleep. The movements are often associated with a partial arousal or awakening; however, the patient is usually unaware of the limb movements or frequent sleep disruption. Between the episodes, the legs are still. There can be marked night-to-night variability in the number of movements or in the existence of movements.

Persistent Insomnia - continuing insomnia responding poorly to treatment.

Pharynx - area posterior to the nares and the oral cavity; passageway for air from the nasal cavity and/or the mouth to the lungs via the larynx and the trachea, for food and liquids from the mouth to the esophagus
Phase advance - movement to a position earlier in the 24 hour sleep - wake cycle of a period of sleep or wake; for example, a shift of the sleep phase from 11 p.m. - 7 a.m. to 8 p.m. - 4 a.m.

Phase delay - Phase delay is exactly the opposite of phase advance, i.e., a shift later in time.

Phasic (Event/Activity) - brain, muscle, or autonomic related event of a brief and episodic nature occurring in sleep. Usually occur during REM sleep, such as eye movements and/or muscle twitches

Photoperiod - duration of light in a light/dark cycle.

Pickwickian Syndrome - obesity accompanied by somnolence, lethargy, chronic hypoventilation, hypoxia, and secondary polycythemia (a condition marked by an abnormal increase in the number of circulating red blood cells); usually has severe obstructive sleep apnea Pineal Gland - gland in the brain secreting the hormone melatonin.

PLMD-Arousal Index - number of sleep-related periodic leg movements per hour of sleep that are associated with an EEG arousal

Polycyclic - multiple sleep periods and wake periods in a 24-hour day.

PO2 - partial pressure of oxygen (O2) in the blood. A value above 60 is usually considered a safe level: lower than 60 indicated hypoxemia and potential danger for the patient.

Polysomnogram (PSG) - continuous and simultaneous recording of physiological variables during sleep, i.e., EEG, EOG, EMG (the three basic stage scoring parameters), EKG, respiratory air flow, respiratory excursion, lower limb movement, and other electrophysiological variables.

Polysomnograph - biomedical instrument for the measurement of multiple physiological variables of sleep

Polysomnographic Technologist - health care professional trained in performing diagnostic sleep studies

Post-Prandial Drowsiness - sleepiness that occurs after a meal, usually lunch

Post-Traumatic Stress Disorder - re-experiencing of a traumatic event in the form of repetitive dreams, recurrent and intrusive daytime recollections, and/or dissociative flashback episodes.

Premature morning awakening - early termination of the sleep period in a sleep maintenance DIMS due to inability to return to sleep after the last of several awakenings

Prescribed CPAP Pressure - pressure(s) or settings determined by a CPAP titration sleep study, which a physician prescribes for a patient's CPAP therapy machine

Pulse Oximetry - non-invasive measure of oxygen saturation; that is the amount of oxygen saturated in the hemoglobin in terms of percentage; not as accurate as the values obtained from an arterial blood gases (ABG) test and should only be used as a gauge of oxygenation. Normal ranges are between 95-100%.

Quiet Sleep - The term frequently used instead of NREM sleep to describe the sleep of infants.

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.