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Sleep Apnea and CPAP Definitions


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

Apnea/Hypopnea index (AHI)

- the number of apneas and hypopneas per hour. 5-15=mild, 15-30=moderate, above 30=severe


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


- 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.

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.


- 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.


– teeth grinding during sleep.


- 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.

Cheyne-Stokes respiration

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

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.


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

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.


- 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.


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

Electrocardiography (EKG)

– a method of measuring the electrical activity of the heart.


- 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).


- 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).

Epworth Sleepiness Scale

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

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.


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

Gastroesphageal Reflux Disease (GERD)

- flow of stomach acid upwards into the esophagus that can cause arousals and disrupt sleep.


- 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.

Inappropriate Sleep Episodes

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


– complaint describing difficulty in sleeping.

Jet Lag

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

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.

Mixed (sleep) apnea

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

Multiple sleep latency test (MSLT)

- a series “nap tests” utilized in the assessment of excessive daytime sleepiness.


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


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


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


- 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.

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.

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.

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%.


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

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.

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.

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.


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

Polysomnographic Technologist

- health care professional trained in performing diagnostic sleep studies.

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%.

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 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.

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.


- surgery on the nasal septum (dividing the nasal passage).


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


- 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 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 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 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 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 paralysis

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

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 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.

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 Transition Disorder

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


- 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.


- walking while asleep.


- prolonged drowsiness or sleepiness.

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.


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


- in pharmacology, refers to the reduced responsiveness to a drug's action as the result of previous continued and/or multiple exposure.


- 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.


- surgical removal of the tonsils.

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.


- 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.