SLEEP GLOSSARY (…from A-Z)

AUSTRLIAN SLEEP HELP GLOSSARY

A

Acetylcholine

Adenosine

Advanced Sleep Phase Syndrome – A circadian rhythm disorder in which phases of the daily sleep/wake cycle are advanced with respect to clock time. The sleep phase occurs well ahead of conventional bedtime, creating a tendency to fall asleep or wake up too early.

Alpha Rhythm – An EEG brainwave produced when an individual is in a relaxed awake condition with their eyes closed. The frequency is 8-13 Hz in human adults, and is predominately present in the occipital lobe of the brain. It indicates the awake state in most normal individuals.

Alpha Sleep – Sleep in which alpha activity occurs with sleep EEG patterns.

Alpha-Delta Sleep – On rare occasions, Delta brainwaves (deep sleep) are mixed with alpha brainwaves (relaxed wakefulness). Alpha-delta sleep occurs with conditions such as arthritic pain, stimulant use and thyroid imbalance.

Ambulatory Monitor – Portable system used for the continuous recording of multiple physiological variables during sleep.

Amygdala

Anticonvulsant – a class of drugs that work to suppress sensory disturbances; they are often used to treat epileptic seizures.

Antidepressant – a type of drug traditionally used to relieve or prevent psychiatric disorders associated with depression, but also used in the treatment of cataplexy, hypnagogic hallucinations, and sleep paralysis.

Antihistamine – a drug that inhibits histamine, a compound that mediates inflammation and produces allergic reactions; antihistamines are a common ingredient in over-the-counter sleeping pills because of their sedative effect.

Apnea – Cessation of breathing for 10 or more seconds during sleep. There are two basic types of sleep apnea: Obstructive Apnea is caused by a closure of the air passage despite efforts to breathe; Central Apnea is a lack of effort to breathe. Obstructive Sleep Apnea is by far the most common type. True apnea during wakefulness is extremely rare.

Apnea/Hypopnea Index – (AHI) (RDI or Respiratory Disturbance Index) The frequency of abnormal respiratory events per hour of sleep. These events are classified as Apneas or Hypopneas. Apnea is when breathing (airflow) stops for 10 seconds or more. Hypopnea is a partial blockage of airflow resulting in arousal and a possible drop in oxygen level. An AHI of 45 would indicate that the patient is experiencing complete or partial airflow blockage 45 times per hour.

Apnea Index – The frequency of apneas per hour of sleep.

Arousal – An abrupt change from sleep to wakefulness, or from a “deeper” stage of non-REM sleep to a “lighter” stage.

Arousal Disorder – A parasomnia disorder presumed to be due to an abnormal arousal function. The classical arousal disorders are sleepwalking, sleep terrors, and confusional arousals.

Arousal Threshold – The ease with which a sleeping person is awakened at a particular time.

Astrocyte

Augmentation – a result of prolonged use of dopaminergic agents in which symptoms (of Restless Legs Syndrome) are chased into the daytime sometimes necessitating daytime dosing.

Automatic Behavior – performing activities or tasks with little or no recollection of the event.

Awakening – The return to the polysomnographically defined awake state from any of the non-REM sleep stages or REM sleep: characterized by alpha and beta waves, rise in tonic EMG, voluntary eye movements and eye blinks.The muscle tone is high and body movement is voluntary.

B

Beta Activity – Brain waves seen in alert wakefulness which have a frequency greater than 13 Hz (Hertz).

Benzodiazepine – a class of central nervous system depressants; examples include Valium (diazepam), Klonopin (clonazepam), Restoril (temazepam), and Halcion (triazolam); useful for managing insomnia, Restless Legs Syndrome, Periodic Limb Movement Disorder, sleepwalking, and REM Behavior Disorder.

Bi-Level Positive Airway Pressure (Bi-level or Bi-PAP) – See CPAP. A CPAP device providing two measured pressure levels of continuous airflow: one level for inhalation and a lower level for exhalation. BiPAP is generally used for apnea patients who can not tolerate high constant air pressure with CPAP.

Bimaxillary Advancement – a surgical procedure in which the upper and lower jawbones and teeth are moved forward and held in place with titanium plates and screws so that soft tissue structures are pulled forward, creating more space for the tongue.

Biological Clock – A term applied to the brain process that regulates 24-hour fluctuations in body temperature, hormone secretion, and a host of other bodily activities. Its most important function is to foster the daily alternation of sleep and wakefulness. The biological clock is housed in a pair of tiny bilateral brain areas called the suprachiasmatic nuclei.

Biological Rhythms (Circadian Rhythms) – An innate daily fluctuation of physiological or behavioral functions, including sleep-wake states generally tied to the 24-hour daily dark-light cycle. Sometimes occurs at a measurably different periodicity (e.g. 23 or 25 hours) when light-dark and other time cues are removed.

Body Position – In sleep studies, four sleep positions are identified; back, left side, right side or abdomen. Some tests also indicate if a patient is sitting up. The amount of time spent sleeping in each position and the occurrence of respiratory events in a particular position are tabulated. Body position is recorded in both diagnostic sleep studies and CPAP titration studies.

Bradycardia – A heart rhythm with a rate below 60 beats per minute in a human adult.

Brain Waves - Spontaneous electrical activity of the brain studied by method of electroencephalography (EEG). They include:.

• Beta Rhythms – Usually associated with alert wakefulness. They are faster than Alpha waves, cycling about thirteen to thirty-five times per second.

• Alpha Rhythms – Most consistent and predominant during relaxed wakefulness, particularly when your eyes are closed or you are in the dark. Alpha rhythms cycle eighteen times per second.

• Theta Rhythms – Associated with the light sleep stage 1 and 2. These cycle four to eight times per second.

• Delta Rhythms – Occur chiefly in deep sleep stages 3-4, also known as slow-sleep. Delta Rhythms cycle less than four times per second

Bright Light Therapy - a treatment used to treat circadian rhythm disturbances; also used to treat Seasonal Affective Disorder (SAD).

Bruxism (Toothgrinding) – Grinding or clenching  one’s teeth while asleep. This occurs at some time in approximately 70% of people; most have no noticeable side effects. However, 5% of victims develop symptoms such as tooth wear, jaw pain and headaches. Episodes of grinding are more severe after stressful days.

C

Cataplexy – a temporary decrease or complete loss of muscle control triggered by an emotional response that is often seen in narcoleptics. Also, a sudden, dramatic drop in muscle tone and loss of deep reflexes, which leads to muscle weakness or paralysis (an attack may cause a person to collapse). It is usually triggered by an emotional stimulus such as laughing or being startled, or by some sudden physical exertion. Cataplexy is a symptom of narcolepsy, a neurologic disorder that causes excessive sleepiness.

Central Nervous System – also called the CNS; the part of the nervous system that consists of the brain and the spinal cord, which are responsible for the coordination of all motor and mental activities.

Central Sleep Apnea – A period of at least 10 seconds without airflow, during which no respiratory effort is evident. It is caused by the brain failing to signal the respiratory muscles to breathe.

Chronic Insomnia – regular sleeplessness that lasts for more than three weeks and is persistent without treatment.

Chronobiology – the scientific study of biological rhythms and timing mechanisms, sleep-wake cycles, heart rate, hibernation cycles, and body temperature.

Chronotherapy – Treatment of a circadian rhythm sleep disorder by systemically changing sleeping and waking times to reset the patient’s biological clock..

Circadian – a cycle that lasts about 24 hours.

Circadian Rhythms – the process of biological variations over 24 hours, coordinated by the suprachiasmatic nuclei in the brain, which regulate body temperature, hormone secretions, and other physiological functions.

Cognitive-behavioral Therapy – psychological therapy which focuses on changing attitudes and beliefs related to sleep and insomnia.

Compulsive Hyperphagia – a disorder of excessive and compulsive overeating; it is often accompanied with other disorders, such as hypersexuality and hypersomnia, and is also associated with Kleine-Levin syndrome.

Continuous Positive Airway Pressure (CPAP) Machine – Medical device used to treat sleep apnea. This apparatus provides a highly effective, non-invasive therapy that eliminates blockages and prevents collapse of the upper airway by generating a prescribed level of air pressure that maintains airway patency during sleep. Air pressure is delivered through a hose to a mask that fits over the nose, or both nose and mouth. The mask is secured on the face by headgear that is worn over the head. The appropriate air pressure level is determined during a “CPAP titration” sleep study. The complete system consists of a programmable pressure generator, tubing, mask and headgear. Sometimes referred to as nCPAP (nasal Continuous Positive Airway Pressure).

Cortisol – (the same as hydrocortisone) a steroid hormone produced in the adrenal gland that influences the metabolism of various cell types

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

D

Deep Sleep (Delta Sleep) (Slow Wave Sleep) – In sleep studies, refers to combined non-REM sleep stages 3 and 4.

Delayed Sleep Phase Syndrome – A circadian rhythm disorder, which in the daily sleep/wake cycle, is delayed with respect to clock time. Accordingly, the sleep phase occurs well after the conventional bedtime. Usually associated with difficulty getting up in the morning.

Delta Sleep (Deep Sleep) (Slow Wave Sleep) – Sleep stages 3 and 4 in which EEG delta waves are prevalent.

Delta Waves - Delta waves have a frequency of 2 cycles per second (cps) or slower and amplitudes greater than 75 microvolts peak to peak (the difference between the most negative and positive points of the wave). Also known as Delta Activity.

Dopamine

Dopaminergic Agents – a class of drugs synthesized with the neurotransmitter dopamine and is most often used to treat Parkinson’s patients; often helpful in managing Restless Legs Syndrome and Periodic Limb Movement Disorder.

Dreams – periods of intense vivid imagery during sleep, often associated with rapid eye movements. Dreams are either consolidating(Non REM sleep dream) or procedural ( REM stage dreaming)

E

Electrocardiography (EKG) (ECG) – Method of measuring the electrical activity of the heart. EKG is continuously recorded in both diagnostic sleep studies and CPAP titration sleep studies.

Electroencephalogram (EEG) – A recording of the electrical activity generated by the brain. Brain wave frequencies are expressed in hertz (Hz) or cycles per second (cps), and amplitude is expressed in microvolts. Characteristic frequency and amplitude patterns of the activity define which stage of sleep the patient is experiencing. Brain waves are recorded in both diagnostic and CPAP titration sleep studies.

Electromyogram (EMG) – A recording of the electrical activity of the muscles. The absence of very low level of EMG activity indicates the presence of REM sleep. Very high levels can help identify periods of wakefulness. Non-invasive EMG is recorded in both diagnostic and CPAP titration sleep studies.

Electrooculogram (EOG) – A recording of the movements of the eyes. If rapid eye movements are detected during sleep, the subject is in REM sleep, which is the state in which vivid dreaming takes place. EOG is recorded in both diagnostic and CPAP titration sleep studies.

Endogenous Circadian Pacemaker - an internal mechanism in the brain, thought to be at the site of the suprachiasmatic nucleus, that drives periodic processes, such as the sleep-wake cycle, body temperature, and cortisol release, in the human circadian timing system.

Enuresis – also called bed-wetting or sleep enuresis; uncontrolled urination during sleep. This disorder is more common in children and often related to maturation; however, repeated nocturnal bed-wetting can indicate other physical or emotional problems.

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

Epinephrine ( adrenalin)

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

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

Esophageal Pressure – A measurement used to determine respiratory effort and by inference, airway resistance. Considered an invasive measure, it is sometimes used in polysomnographic testing that is conducted in sleep disorders centers.

Excessive Daytime Sleepiness (EDS, Somnolence, Hypersomnia) – A subjective report of difficulty in maintaining the awake state, accompanied by a ready entrance into sleep when the individual is sedentary; may be quantitatively measured by use of subjectively defined rating scales of sleepiness.

Excitotoxicity

F

“Factor S” - a substance in the cerebrospinal fluid that has sleep-inducing properties.

Fragmentation (pertaining to Sleep Architecture) – The interruption of a sleep stage due to the transition to a lighter stage, or to wakefulness, leading to disrupted sleep cycles.

G

GABA

Gastroesphageal Reflux Disease (GERD) – The flow of stomach acid upwards into the esophagus, which can cause arousals and disrupt sleep.

Genioglossus muscle – a muscle that attaches from the back of the tongue to a region on the back of the chin and serves to advance, retract and depress the tongue.

Genioglossus tongue advancement – Surgical treatment sometimes used for sleep apnea or snoring. This is designed to improve the airway behind the base of the tongue. The genioglossus, which is the main tongue muscle, relaxes during sleep, often allowing the tongue to fall into the airway. This muscle attaches to the middle of the lower jaw. If a segment of bone containing this muscle is pulled forward and stabilized, it can open the airway space behind the tongue. This procedure does not move the teeth or jaw. It is performed under local intravenous sedation or general anesthesia and requires a one or two day hospital stay.

Glial cells

Glossectomy – the surgical reduction or removal of the tongue, used to open the lower airway or to remove cancerous tissue.

G-proteins

Glutamate

H

Hertz (Hz) – the unit of measurement for cycles per second; used to measure EEGs.

Histamine

homeostatic – (homeostasis, n.) the balanced state of the living body (i.e. temperature, chemistry, blood pressure, sleep and wakefulness, and so on), despite variations in the environment.

Hyoid Suspension/ Hyoid advancement – Surgical procedure sometimes used in the treatment of sleep apnea or snoring. It is designed to improve the airway behind the base of the tongue. The hyoid bone is located in the neck where some tongue muscles attach. If the hyoid bone containing these muscles is pulled forward in front of the voice box, it can open the airway space behind the tongue. This is performed under local intravenous sedation or general anesthesia, and requires a one or two day hospital stay.

hyoid bone – a C-shaped bone in the upper neck positioned above the Adam’s apple with muscle attachments to the back of the tongue, as well as the sides of the lower throat.

Hypercapnia – An excess of carbon dioxide in the blood.

Hypersomnia – also called excessive (daytime) sleepiness or somnolence Sleeping for uncharacteristically long periods of time; the inability to remain awake during an individual’s normal wake period.

Hypersomnolence – Excessive daytime sleepiness.

hypnagogic hallucinations – vivid, often frightening, dream-like images and sounds experienced at REM sleep onset, usually accompanied by fear and anxiety; a characteristic feature of narcolepsy.

Hypnophobia – Morbid fear of falling asleep.

hypnic jerk – also called sleep starts; the sensation of falling and then a physical jerk into wakefulness, usually during Stage 1 sleep.

hypnotic – also called a sleeping pill, sedative, or a sedative-hypnotic medication; a medication that causes drowsiness, induces sleep onset, and/or maintains sleep.

“hypnotoxin” – also called sleep promoting substance (SPS); the term coined by Henri Pieron in 1907 that described a sleep-inducing substance thought to be in the cerebrospinal fluid.

Hypopnea – An episode of diminished breathing during sleep, caused by a partial airway obstruction, and resulting in arousal. Usually accompanied by oxygen desaturation. Hypopneas may be just as serious as apneas and have the same troublesome effects.

hypothalamus – the region at the base of the brain involved in autonomic processes such as temperature regulation, food intake, and emotional activity, and thought to be important in the role of sleep and wakefulness.

Hypoxemia – Lack of an adequate amount of oxygen in the blood.

Hypoxia – A deficiency of oxygen reaching the tissues of the body

I

idiopathic – occurring spontaneously and without known cause.

idiopathic hypersomnia – a disorder of excessive sleepiness in which the affected individual sleeps longer than normal (greater than 10 hours), is excessively sleepy, falls asleep at inappropriate times, and frequently takes naps. Its exact cause is unknown.

insomnia – the inability to sleep applied to the general complaint of having trouble falling or staying asleep; insomnia is a symptom usually caused by underlying problems. See also transient, short-term, chronic, and sleep onset insomnia.

J

Jet Lag – A disturbance induced by a major rapid shift in environmental time during travel to a new time zone(usually 3 of more zones) and is characterized by various psychological and physiological effects, such as fatigue, gastrointestinal disturbances, and irritability, sleepy and impaired alertness, caused by a disruption in circadian rhythms.

K

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

K-complex – high voltage EEG activity that consists of a sharp upward component followed by a slower downward component and lasts more than .5 seconds immediately followed by a slower positive component.

Kleine-Levin syndrome – a disorder distinguished by recurrent hypersomnia, compulsive overeating, and hypersexuality and first described by Willi Kleine in 1925 and then by Max Levin in 1929.

L

lark – also called a morning person or morning lark; a person who prefers go to bed early in the evening and rise early in the morning.

Laser Assisted Uvuloplasty (LAUP) – Surgical treatment usually used for simple snoring or mild obstructive sleep apnea. This procedure is designed to open the airway behind the palate. It requires multiple procedures where the laser reduces tissue of the palate and the area heals by scarring. It is an outpatient procedure performed under local anesthesia.

latency period – an interval. Sleep latency is the interval from “lights out” until sleep begins. REM latency is the period from the beginning of sleep to the first appearance of rapid eye movement (REM) sleep.

L-Dopa – also called dopaminergic agents; a dopamine-enhancing class of drugs most often used to treat Parkinson’s patients; often helpful in managing Restless Legs Syndrome and Periodic Limb Movement Disorder. Examples include L-Dopa with Sinemet (carbidopa), Permax (pergolide), and Parlodel (bromocriptine).

Leg Movement – Leg movements are recorded in diagnostic sleep studies to test for Periodic Limb Movement Disorder.

“leucomaines” – the name for the poisonous substances that supposedly accumulated during the day and passed from the blood to the brain. Leo Errera proposed that these substances in the 1880s were the cause of sleep.

Light Therapy – Used to treat SAD (Seasonal Affective Disorder) , Advanced Phase Sleep Disorder, or Delayed Phase Sleep Disorder, Depression,  and Hypersomnia. It involves Exposing the eyes to light of appropriate intensity and duration at the appropriate time of day to affect the timing, duration and quality of sleep.

lingualplasty – a surgical procedure that involves a resection of the tongue with additional removal of side wedges in order to reduce the back of the tongue and open the lower airway.

lingual tonsils – tonsil-like tissue on the back part of the tongue.

lux – a measure of light intensity; the unit used by light box manufacturers to describe light output.

M

maintenance of wakefulness test – also called MWT, a test that consists of four 20-minute trials conducted every 2 hours and is used to determine a patient’s ability to stay awake during the day. Contrary to a MLST, the MWT is scored on the patient’s ability to remain awake during the trials.

Maxillofacial – Pertains to the jaws and face.

Maxillomandibular advancement – This surgical procedure opens the airway behind the palate as well as behind the base of the tongue. The operation cuts the bone of the upper and lower jaw and pulls these structures forward. This is performed under general anesthesia and requires a two-day hospital stay. This type of treatment is usually done if previous procedures have not completely improved the obstructive breathing episodes and the patient has persistent symptoms of daytime sleepiness and fatigue.

melatonin – in nature, a hormone that is secreted by the pineal gland in the brain in response to darkness, and has been linked to regulation of circadian rhythms; a derivative of melatonin marketed as a health food supplement is commercially available.

mental imagery – the process of creating images in the mind.

Microsleep – Very brief episode of sleep that occurs in the midst of ongoing wakeful activity. Microsleeps are associated with sleep deprivation, drowsiness and automatic behavior.

Mixed Sleep Apnea – Combination of central and obstructive sleep apnea.

montage – the term applied to the testing variables and their order on polysomnogram paper or a computer monitor, such EEG, EOG, heart rate, and so on.

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

Motor Activity in Sleep – Any muscular movement during sleep.

Motor Atonia – Absence of muscle activity during sleep, a normal phenomenon during REM sleep.

Movement Arousal – A body movement associated with an EEG pattern of arousal or a full awakening.

Multiple Sleep Latency Test (MSLT) – The standard test used to quantify the overall daytime sleep tendency by measuring the speed of falling asleep (sleep latency) usually in 5 tests carried out at two-hour intervals. This test also helps in the diagnosis of narcolepsy. Patients with narcolepsy often go directly from wakefulness to REM, which can be evaluated with the MSLT.

Muscle Tone – The amount of tension in a muscle.

Myoclonus – Muscle contractions in the form of abrupt “jerks” or twitches generally lasting less than 100 milliseconds. The term should not be confused with the periodic limb movements of sleep that characteristically have a duration of 0.5-5 seconds.

MWT –  an acronym for the maintenance of wakefulness test, in which four 20-minute trials are conducted every two hours and the patient is encouraged to stay awake.

N

Narcolepsy – A sleep disorder characterized by excessive sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations, and an abnormal tendency to pass directly into REM sleep from wakefulness. It was recently found to be caused by an abnormal gene in the brain.

negative sleep conditioning – a psychological state perpetuated by self-induced stress and anxiety of needing to attain sleep; specifically, it refers to an inability to sleep at night in one’s own bed.

neuron – a type of nerve cell (or brain cell) that has a central cell body (axon) and long endings (dendrites) specialized to receive, conduct, and transmit signals in the nervous system.

Nightmare – An unpleasant and/or frightening dream that usually awakens a person from REM sleep. Occasionally called a dream anxiety attack, it is not synonymous with a night (sleep) terror.

Night Terrors – Also known as sleep terrors, or pavor nocturnus. Usually a disorder of childhood, characterized by a piercing scream, signs of intense fear, and unresponsiveness to other people. It is not a REM stage nightmare, but an incomplete arousal from slow wave sleep. If awakened during a night terror, the individual is usually confused and does not remember details of the event. Night terrors are different from nightmares in that if an individual is awakened during a nightmare, he or she functions well and may have some recall of the nightmare.

night owl – also called a night person or evening person; a name applied to someone who prefers to stay up into the night or early morning and arise in late morning.

Nitric Oxide

nocturia – also called nycturia; frequent urination at night that results in arousal of sleep and rising frequently to go to the bathroom. It can be caused by urological problems, infection, a tumor, or medication and has been associated with the development of obstructive sleep apnea.

nocturnal – of the night or night-related; the opposite of diurnal.

Nocturnal Enuresis (Bedwetting) – The release of urine while asleep

nocturnal myoclonus – a brief rapid twitch that occurs at night as a result of a sudden contraction of one or more muscle groups; former name of Periodic Limb Movement Disorder.

normal hypersomnia – a disorder in which the affected individual requires more sleep than normal, i.e. more than 10 hours of sleep per day, and which may be the result of a genetic predisposition. Normal hypersomniacs are also called “naturally long sleepers.”

NREM Sleep (Non-Rapid Eye Movement, Non-Rem) – All sleep stages other than REM sleep; made up of sleep stages 1 through 4. Characterized by a slowing of brain waves and some physiological functions. A state that lacks the visible motility of rapid eye movements and twitches. See Sleep Stages.

NREM-REM Sleep Cycle (synonymous with Sleep Cycle) – A period during sleep composed of a NREM sleep episode followed by a REM sleep episode. Each NREM-REM sleep couplet is equal to one cycle; with the average duration in adults being 90 minutes. An adult sleep period of 6.5-8.5 hours generally consists of four to six cycles.

Nyctophobia – Morbid fear of the night and darkness

O

Obstructive Hypopnea – Periodic, partial closure of the throat during sleep resulting in reduced air exchange. The medical consequences of this partial closure can be as severe as sleep apnea (full closure of throat) Usually characterized by snoring, excessive daytime sleepiness, and other symptoms of fatigue

Obstructive Sleep Apnea – Repetitive cessation of breathing during sleep for 10 seconds or more due to complete closure (collapse) of the throat. Usually characterized by snoring, excessive daytime sleepiness, and other symptoms of fatigue.

opiate – a class of codeine-derived, controlled narcotics, such as Tylenol #3, Percocet (oxycodone), Darvon (propoxyphene) and methadone; used to manage severe cases of Restless Legs Syndrome and Periodic Limb Movement Disorder.

OTCs – an acronym for over-the-counter medications, those that are available for purchase without a prescription.

OSA – an acronym for obstructive sleep apnea; a common form of apnea

otolaryngology – the medical study of the ears, nose, and throat (ENT)

Oxygen Desaturation – Less than normal amount of oxygen carried by hemoglobin in the blood. A value below 90% is considered abnormal.

Oxygen Saturation – A measure of oxygen carried by hemoglobin in the blood. Normal values range from 90% to 100%. An important indicator of sleep disordered breathingthat is directly affected by the degree of throat closure (partial vs. complete) and its duration. Oxygen saturation is recorded in both diagnostic sleep studies and titration studies.

Oximeter – Medical device used to provide estimates of arterial oxygen saturation (SaO2) by utilizing selected wavelengths of light to noninvasively determine the saturation of oxyhemoglobin (SpO2).

P

paradoxical therapy –  an effective therapeutic approach to conquering insomnia that asks the insomniac to do the exact opposite of trying to fall asleep.

Parasomnia – Disorders that intrude into the sleep process and involve physical and behavioral manifestations during arousal, partial arousal, and sleep stage transition. These disorders occur most frequently with children and usually occur in NREM sleep stages. Common parasomnias are night terrors, sleep walking (somnambulism), and sleep-related bruxism (teeth grinding). They are divided into four groups: Arousal Disorders, Sleep-Wake Transition Disorders, Parasomnias Usually Associated with REM Sleep, and Other Parasomnias.

pavor nocturnus – a term derived from Latin pavor, terror, and nocturnus, at night. See also sleep terrors.

Perceptual Disengagement – Refers to 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 – Characterized by repetitive short apneic pauses, common in premature infants.

Periodic Limb Movement Disorder – Also known as Periodic Leg Movements of Sleep and Nocturnal Myoclonus. Characterized by periodic episodes of repetitive limb movements 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. . There can be marked night-to-night variability in the number of movements.

periodic limb movement index – the record of the number of leg or arm movements during each hour of sleep measured by sensors placed on the legs and arms.

Persistent Insomnia – Continuing insomnia that responds poorly to treatment

Phasic (Event/Activity) – Brain, muscle, or autonomic event of a brief and episodic nature occurring in sleep. Characteristically occurs during REM sleep, such as eye movements and/or muscle twitches, and can last from milliseconds to 1-2 seconds.

Pickwickian syndrome – the first term applied to obstructive sleep apnea, originally described by Charles Dickens in 1836. It referred to people who were excessively sleepy, loud snorers, and overweight.

PLMD – an acronym for Periodic Limb Movement Disorder; a condition in which the legs or arms twitch or move involuntarily and periodically during sleep.

PLMD-Arousal Index – The number of sleep-related periodic leg movements per hour of sleep that are associated with a micro-arousal from sleep. See Periodic Leg Movement Disorder.

Polycyclic – In reference to sleep, multiple sleep periods and wake periods in a 24-hour day.

polyp – a projecting growth or mass, usually benign, that forms in a mucous membrane and in the nasal passages, causes obstructed airflow.

polysomnogram – also called a PSG, sleep study, or sleep test; a non-invasive test that records vital signs and physiology during a night of sleep. It includes measurements from an EEG, EMG, and EOG, as well as respiratory airflow, blood oxygen saturation, pulse rate, heart rate, body position, and respiratory effort.

postprandial dip – a slight drowsiness caused by a natural drop in body temperature, particularly in early afternoon and after a meal.

post-traumatic hypersomnia – a disorder of excessive sleepiness that appears within 18 months of a traumatic event involving a central nervous system-related accident.

primary snoring – snoring not associated with apnea.

Process C – the natural behavior and tendency, regulated by human circadian rhythms, to sleep during the “sleepy phase” of the body, usually between 11:00 p.m. and 7:00 a.m.

Process S – also known as the homeostatic process, it is the disposition of a normal person who is sleep-deprived to become sleepy when awake, and sleep deeper and longer when sleep is achieved.

Prostaglandin D2

Prostaglandin E2

pupillometry – the measurement of pupil diameter and activity as related to alertness or sleepiness. This test is used more for research rather than a diagnostic assessment.

R

Radio-frequency tissue ablation – a technique that uses radio-frequency waves via a needle electrode placed under the surface of the tissue, resulting in contraction and subsequent shrinkage of excessive tissues that cause snoring.

Recurrent hypersomnia – a disorder of excessive sleepiness that occurs weeks or months apart, often accompanied with other disorders such as hypersexuality or compulsive eating.

Relaxation therapy – also termed relaxation imagery; various methods or techniques for the alleviation of insomnia that help to relax the mind and the body and which can facilitate sleep onset.

REM Motor Atonia – The suppression, or paralysis, of voluntary muscles during REM sleep. These muscles become completely flaccid and limp.

REM Sleep (Rapid Eye Movement Sleep) – The sleep stage in which vivid dreaming occurs; identified by the occurrence of rapid eye movements under closed eyelids, motor atonia and low voltage EEG patterns. Also associated with bursts of muscular twitching, irregular breathing, irregular heart rate, and increased autonomic activity.

REM Sleep Behavior Disorder – A disorder in which REM motor atonia is partially or completely absent. People with this disorder are able to move their muscles and act out their dreams. The behaviors may include punching, kicking, leaping and running from the bed.

REM Sleep Episode – The REM sleep portion of a NREM-REM sleep cycle. There are typically 4-6 REM sleep episodes during an entire sleep period. Early episodes may be only several minutes in duration. Later REM episodes are usually longer, lasting 20 to 60 minutes.

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

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

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

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

REM Sleep Rebound – A compensatory increase in REM sleep following a reduction of REM Sleep Percent.  An increase in time, frequency and density of REM sleep episodes.

Respiratory disturbance index (RDI) – a record of the number and duration of apnea episodes, both obstructive and central, during each hour of sleep. An RDI of greater than 5 is regarded as abnormal.

Restless Legs Syndrome –  The sleep disorder characterized by tingling, creeping, crawling, or aching sensation in the legs that tends to occur when an individual is not moving. There is an almost irresistible urge to move the legs that relieve the sensations. Inability to remain at rest can result in severe sleep disturbance.

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

S

SCN – an acronym for suprachiasmatic nuclei and sometimes called the endogenous circadian pacemaker; small structures in the brain, sensitive to the presence or absence of light, that coordinate circadian rhythms.

Sedative – also called a sleeping pill or hypnotic; a medication that causes drowsiness, induces sleep onset, and/or maintains sleep.

Selective serotonin reuptake inhibitors – a class of antidepressants that assist nerve impulses along pathways using the neurotransmitter serotonin; effective in treating narcolepsy symptoms. Examples include: Zoloft, Prozac, and Paxil.

Septoplasty – a surgery sometimes used to treat obstructive sleep apnea in which a small incision is made inside a nostril, and the cartilage and bone of the septum is straightened.

Seasonal Affective Disorder (SAD) – A mood disorder occurring in the winter months characterized by diminished energy, hypersomnia, overeating and depressed mood. Exposure to bright light in the morning hours may be effective in alleviating or decreasing symptoms. Symptoms usually diminish with the onset of spring.

Septum – the divider between the two nasal passages; if deviated (crooked), the septum can obstruct the nasal passages.

Serotonin – a neurotransmitter found in brain stem cells and other parts of the central nervous system; in animal studies, the inhibition of the formation of serotonin led to severe insomnia.

Short-term insomnia – temporary sleeplessness that arises because of ongoing stress, a temporary illness, or a traumatic experience.

Sleep – a physical and mental resting state in which a person becomes relatively inactive and unaware of his or her environment.

Sleep Apnea – Cessation of breathing for 10 or more seconds during sleep. There are two basic types of sleep apnea: Obstructive Apnea is caused by a closure of the air passage despite efforts to breathe; Central Apnea is a lack of effort to breathe. Obstructive Sleep Apnea is by far the most common type.

Sleep Debt – The result of recurrent sleep deprivation that occurs over time, when an individual does not obtain a sufficient amount of restorative daily sleep. Sleep debt is like a monetary debt; it must be paid back at some time. The larger the sleep debt, the stronger the tendency to fall asleep. This accumulation of “lost sleep” may contribute to a decreased quality of life, the onset of related health problems, and the increased risk of injury and/or accident. See Sleep Deprivation.

sleep efficiency – the proportion of sleep in the period potentially filled by sleep; that is, the ratio of total sleep time in bed.

sleep hygiene – the practice of achieving and maintaining proper habits to promote good sleep.

Sleep Inertia – Feelings of grogginess and sleepiness that persist up to 20 minutes after waking up. This results in poor performance upon awakening.

Sleep Latency – The length of time it takes to go from full wakefulness to the moment of sleep.

sleep maintenance insomnia – one or more episodes of wakefulness that occur later in the night and may be due to medical illness, primary sleep disorders, or depression.

sleep medicine – the science of the study of sleep and its processes; also refers to the clinical practice of assessing and treating sleep disorders.

sleep paralysis – a brief loss of muscle control that occurs at the onset of sleep or upon awakening; a condition usually associated with narcolepsy. May last from a few seconds to a few minutes. Occurs in one in twenty healthy people but is more common in those with narcolepsy.

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

sleep onset – the transition from the awake to the sleep state, normally into NREM stage 1 (but in certain conditions, such as infancy and narcolepsy, into REM.) Most polysomnographers accept EEG slowing, reduction and eventual disappearance of alpha activity, presence of EEG vertex spikes and slow rolling eye movements (the components of NREM stage 1) as sufficient for sleep onset; others require appearance of stage 2 wave forms. (See sleep latency, sleep stages.)

sleep onset insomnia – insomnia characterized by a delay in falling asleep, lasting 30 minutes or longer, at the time when one goes to bed; it is most commonly caused by anxiety.

Sleep Paralysis – Sleep paralysis is a common part of REM sleep itself but is a disorder when it strikes outside REM sleep. Usually, people with sleep paralysis are unable to perform voluntary movements either right before they go to sleep or upon waking in the morning. One of the symptoms of narcolepsy, but also experienced by some non-narcoleptic individuals.

Sleep Spindle – A synchronized, rhythmic EEG waveform, with a duration of about ½ second and a frequency of 12 to 14 Hz. Sleep spindles are observed most frequently during stage 2 sleep.

Sleep talking – Talking in sleep that usually occurs in the course of transitory arousals from NREM sleep. Can occur during REM sleep, at which time it represents a motor breakthrough of dream speech. Full consciousness is not achieved and no memory of the event remains. Sleep talking probably carries no psychological or psychiatric significance, and the content should be taken very lightly.

Sleep walking (Somnambulism) – Arising from bed during a period when there is a simultaneous occurrence of incomplete wakefulness and NREM sleep. The eyes are usually open, but appear not to be focusing. If victims do not awaken during the episode, they do not remember the event.  An extremely common phenomenon, occurring in up to 40 percent of children, with a peak incidence at 12 years of age. Sleepwalking typically occurs in the first third of the night during deep NREM sleep (stages 3 and 4).

Sleep-Wake Transition Disorder – Parasomnia disorders that occur during the transition from wakefulness to sleep or from one sleep stage to another. These disorders include rhythmic movement disorders, hypnic jerks (sleep starts), sleep talking, and nocturnal leg cramps.

Slow Wave Sleep (SWS) – synonymous with sleep stages 3 and 4.

Snoring – Sounds made during sleep caused by breathing vibrations in the pharynx. In the diagnosis of obstructive sleep apnea, snoring volume and frequency of occurrence often correlate with the severity of the condition. Snoring noise is recorded in both diagnostic sleep studies and CPAP titration studies.

Soft Palate – The membranous and muscular fold on the roof of the mouth that extends back from the hard palate and partially separates the oral cavity from the pharynx.

somnambulism – see also sleepwalking; a parasomnia characterized by walking or performing other complicated activities while asleep.

somniloquy – (somniloquism) see also sleep talking; a parasomnia characterized by talking during sleep.

somnolence – also called excessive sleepiness or excessive daytime sleepiness; the inability to stay awake during the normal wake period of a sleep-wake cycle. It can be measured by a multiple sleep latency test (MSLT)

somnologist – a specialist in the study of sleep and in the diagnosis and treatment of sleep disorders.

somnoplasty – a non-invasive procedure that uses radio frequency to reduce structures in the mouth in the treatment of snoring and obstructive sleep apnea.

Stage 1 sleep – the brief, dozing stage of non-REM sleep in which a person transitions to very light sleep and can be awakened easily, characterized by low voltage EEG and slow rolling eye movements; 5% of non-REM sleep is spent in Stage 1.

Stage 2 sleep – the stage of consolidated sleep in non-REM sleep characterized by sleep spindles and K-complexes; 45% of non-REM sleep is spent in Stage 2.

Stage 3 sleep – the stage of deeper sleep in non-REM sleep characterized by delta waves interspersed with smaller, faster waves; 12% of non-REM sleep is spent in Stage 3.

Stage 4 sleep – the stage of very deep sleep in non-REM sleep almost exclusively composed of delta waves and the stage in which sleep terrors or sleepwalking may occur; 13% of non-REM sleep is spent in Stage 4.

stimulant – a type of drug, such as Cylert, Ritatlin, and Dexedrine, that stimulates the central nervous system; often used to treat excessive daytime sleepiness.

stimulus control – an effective insomnia technique developed by Dr. Richard Bootzin and colleagues which proposes that an individual has 10 minutes to fall asleep. If sleep is not achieved, the person must get up, go into another room, and return to bed only when sleepy. Also called the 10-minute rule.

suprachiasmatic nuclei – also called the SCN or the endogenous circadian pacemaker; small structures in the brain, sensitive to the presence or absence of light, that coordinate circadian rhythms.

T

Taurine

The 10-Minute Rule – a relaxation and sleeping technique that suggests that an individual who has laid awake in bed for an estimated 10 minutes to get up, go into another room, relax by doing something boring, and then return to bed when sleepy.

Thoracic Excursion – Thoracic (chest) movement, which indicates respiratory effort. This is recorded in diagnostic sleep studies, and is typically measured by the placement of a sensor band around the chest. The sensor band records chest wall movement associated with respiration. This measurement is used in differentiating the type of sleep apnea.

Tidal Volume – The amount of air that passes in and out of the lungs in an ordinary breath. Usually expressed in liters.

Tonsils – masses of lymphoid tissue at the back of both sides of the mouth whose primary function is fighting infection.

Tonsillectomy – surgical removal of the tonsils.

Toothgrinding (Bruxism) – Grinding one’s teeth while asleep. This occurs at some time in approximately 70% of people; most have no noticeable side effects. However, 5% of victims develop symptoms such as tooth wear, jaw pain and headaches. Episodes of grinding are more severe after stressful days

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

Total sleep time – the amount of actual sleep time in a sleep period; equal to total sleep period less movements and awake time. Total sleep time is the total of all REM and NREM sleep in a sleep period.

Tracheostomy – also known as a tracheotomy; a surgical procedure that creates an opening in the windpipe via the neck in order to insert a tube that facilitates breathing. This procedure is reserved for patients with severe sleep apnea.

Transient insomnia – sometimes called adjustment sleep disorder or situational insomnia, it is sleeplessness that lasts a few consecutive nights and is often triggered by stress or excitement

Tricyclic Antidepressants (Antidepressants) – A class of medications most commonly used in the treatment of depression. Tricyclic refers to the three-ring chemical structure. Most tricyclic antidepressants also reduce REM sleep. In sleep disorders, they are used to control cataplexy, hypnagogic hallucinations, and sleep paralysis.

Tryptophan

Turbinate – also called the nasal concha; any of three bones (lowest, middle, and upper) within the nose that are surrounded by soft tissue and form the sides of the nasal cavity.

Turbinate reduction – a surgical procedure used to reduce the size of an enlarged turbinate, which can improve the size of the nasal airway, thereby relieving obstructive sleep apnea.

Tyrosine

Twilight Zone – A slang term that describes 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

Upper Airway Resistance Syndrome – 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. Usually associated with loud snoring. Apneas and hypopneas (see RDI) may be totally absent. Blood oxygen levels can be in the normal range.

U

UPPP – an acronym for uvulopalatopharyngoplasty; the surgical procedure for the removal of the uvula and tightening of loose tissue in the back of the throat.

“urotoxins” – coined by Abel Bouchard in 1886, a term he used to describe toxic agents excreted in the urine during sleep.

uvula – the tissue that hangs down in the back of the throat.

Uvula – Small soft structure hanging from the bottom of the soft palate in the midline above the back of the tongue. It is composed of connective tissue and mucous membrane.

Uvulopalatopharyngoplasty (UPPP) – Surgical treatment for obstructive sleep apnea and snoring. This procedure is designed to open the airway behind the palate. The uvula, tonsils, and excess palatal tissue are removed. The incision is closed with sutures. The procedure is performed under general anesthesia and usually requires a one or two day hospital stay.

Zeitgeber – An environmental time cue that entrain 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.