Sleep Disorders Glossary 

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

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

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. The average adult needs 7.5-8 hrs of sleep daily.

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. Bi-Level is a benefit for patients with emphysema, morbid obesity, and have neuromuscular disease.

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.

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.

Cheyne-Stokes Respiration - Breathing pattern typified by at least 3 consective cycles of "crescendo-decrescendo" or waxing and waning fluctuations in respiratory rate and tidal volume.

CPAP (Continuous Positive Airway Pressure)- The device used to treat sleep apnea by sending positive airway pressure at a constant, continuous pressure to assist in keeping 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). Different patients require different pressures. The value is determined in a CPAP titration study.

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

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

Electrodes - Small gold, circular devices transmitting biological electrical activity from subject to polygraph.

Epoch - A standard 30 second duration of the sleep recording that is assigned a sleep stage designation.

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

Excessive daytime sleepiness or somnolence (EDS) - Subjects perspective of difficulty in staying awake, accompanied by a strong desire for sleep when the individual is sedentary.

Fatigue - Feeling of tiredness or weariness.

Fibromyalgia - A disease syndrome whose primary symptoms are muscle pain and fatigue.

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

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

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.

Hypopnea - Shallow breathing in which the air flow in and out of the airway is less than half of normal lasting 10 seconds or more. 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.

Insomnia - Difficulty in sleeping.

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

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.

Multiple Sleep Latency Test (MSLT) - A series of "nap tests" utilized in the assessment of excessive daytime sleepiness.

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

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.

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 Enuresis (Bedwetting) - Urinating while asleep.

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.

Obstructive Apnea - Cessation of airflow (at least 10 seconds) in the presence of continued inspiratory effort.  

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 with continued abdominal and thoracic effort.

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.

Periodic Limb Movement Disorder - Also known as periodic leg movements and nocturnal myoclonus. Characterized by periodic episodes of repetitive and highly stereotyped limb movements occurring 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. Legs movements are recorded in a diagnostic and titration study.

Polysomnogram (PSG) - Continuous and simultaneous recording of physiological variables during sleep, i.e., EEG, EOG, EMG, EKG, respiratory air flow, respiratory excursion, lower limb movement, and other electrophysiological variables.

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 20-25% of sleep in adults.

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.

Sleep Apnea - Cessation of breathing for 10 or more seconds during sleep.

Sleep Deprivation - Acute or chronic lack of sufficient sleep.

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-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 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;  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.

Snoring - Noise produced primarily with inspiratory respiration during sleep owing to vibration loose tissure of the soft palate. Many snorers have incomplete obstruction of the upper airway, and may develop obstructive sleep apnea.

Somnambulism - Walking while asleep.

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.

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%.  

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.

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Sleep Patient Stories

Jim Mertens of WQAD-TV shares his personal sleep disorders story in a three-part series. Watch the story here.

Jim Mertens

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