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

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

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

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

Basic Sleep Cycle - Progression through orderly succession of sleep states and stages. For the healthy adult, the first cycle 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 (BiPAP) - 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)

Central apnea - Absence of airflow and inspiratory effort; apnea caused by irregularity in the brain's control of breathing.

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.

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

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.

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.

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.

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

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

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

Insomnia - Complaint describing difficulty in sleeping.

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

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

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.

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

Nightmare - Unpleasant and/or frightening dream occurring in REM sleep. (Different from a night terror)

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 amount of tissue in the uvula area.

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

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.

Polysomnographic Technologist - Health care professional trained in performing diagnostic sleep studies and has achieved a passing grade on the RPSGT board exam.

RDI - Respiratory Disturbance Index - includes all respiratory events per hour.

REM rebound or recovery - Lengthening and increase in frequency and density of REM periods, which results in an increase in REM percent above base line. REM rebound follows REM deprivation once the inhibitory influence is removed.

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

Sleep architecture - NREM/REM stage and cycle infrastructure of sleep understood from the vantage point of the quantitative relationship of these components to each other.

Sleep 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, and abnormalities in physiological functions during sleep, abnormalities of the biological clock, and sleep disturbances that are induced by factors extrinsic to the sleep process.

Sleep efficiency (SE) - Proportion of sleep in the period potentially filled by sleep - ratio of total sleep time to time in bed.

Sleep 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.

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.

Smart PAP (Smart CPAP) - (Smart [Continuous] Positive Airway Pressure) Medical device used in the treatment of obstructive sleep apnea providing preset levels of continuous airflow, and automatically adjusting to keep the breathing passages open by sensing changes in airway integrity. The air flows from the device through a tube that connects to a nose or face mask.

Somnolence - Prolonged drowsiness or sleepiness.

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

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.