Sleep Apnea Definitions – A To H

These are a list of common Sleep Apnea terms and definitions with letters starting from I to Q as used in discussions about Sleep Apnea.
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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. Less than 5 = Normal, 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.

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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.

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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 thoughout 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.

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