Common Terms on CPAP, Sleep Apnea and Sleep Study


A-Flex is a technology by Respironics that enhanced the sensation of breathing when using Auto-CPAP pressure.  Pressure assistance and relief is delivered on inhalation (as necessary) as well as exhalation to provide a more natural sensation of breathing while against an auto adjusting positive pressure.

AHI/RAI Scale is a measurement of both the Apnea/Hypopnea Index (QHI) and the Respiratory Arousal Index. If a person has less than 5 events per hour then that person's AHI/RAI would be 0 and that person would not have apnea. 5 -15 events/hour = (mild); 15-30 events/hour = (moderate); >30 events/hour = (severe).

Apnea is the cessation of airflow for 10 seconds or greater.

AHI (Apnea Hypopnea Index) is the number of apneas and hypopneas per hour. Or an index for sleep apnea. 5-20 mild, 21-50 moderate, above 50 severe. Learn more here

Arousal: An interruption of sleep lasting greater than 3 seconds.

Automatic altitude adjustment allows the patient to travel to different altitudes without having the pressure setting adjusted. Because atmospheric pressure changes with altitude, most machines need adjustment in order to provide the correct pressure at a different altitude. see also Manual Altitude Adjustment

AutoPAP machine has a range of low/high pressures, customizable within 4 - 20 cm H2O automatically detected apneas and/or hypopneas events and deliver the right pressure to keeps the upper airway open.


Bi-Level / BiPAP: Positive Pressure Therapy delivered through dual flow of inspiratory pressure and expiratory pressure.

Body Position: Sleeping position 

Brain Waves: Electrical activity studied by electroencephalography (EEG)

Bruxism: Grinding of the teeth.


Cardiac Arrest: Sudden cessation of the heart.

Central apnea: A respiratory episode where there is no airflow and no effort to breathe lasting greater than 10 seconds.

Cheyne-Stokes Respiration (CSR): A periodic breathing pattern observed with an increasing and decreasing in respiratory rate and tidal volume. Usually seen in patients with Congestive Heart Failure (CHF).

Continuous Positive Airway Pressure (CPAP): A positive airway pressure device used to splint the airway open. The primary treatment option to manage obstructive sleep apnea.


EEG/EOG: Comments about sleep stages, brain waves (EEG), or eye movements (EOG)

EKG/ECG: Comments about heart rate, abnormal heart beats, etc.

EMG: Comments about leg movements and or teeth grinding (bruxism).

ENT Physician: A doctor specializing in Ear, Nose and Throat and normally perform surgical repair or reconstruction in these areas.

Epworth Sleepiness Scale: A series of questions to quantify an individuals tendency to feel sleepy during certain situations.

Excessive Daytime Sleepiness (EDS): A subjective description of hypersomnolence in different situations.


Fatigue : Feeling tired.

Flow Limitation: The partial closure and restriction of the upper airway to prevents effective flow of air into the lungs.


Habitual Snorers: Individuals who snore nearly every night.

Humidification: The addition of moisture to CPAP or BiPAP therapy to minimize dryness resulting from the constant airflow delivered during therapy.

Hypertension: High blood pressure

Hypopnea: A respiratory episode where there is partial obstruction of the airway lasting greater than 10 seconds. Also called partial apnea or hypo-apnea.

Hypoventilation: Reduced rate and depth of breathing resulting a low movement of volume of air to the lungs.

Hypoxemia: Reduction of oxygen content in the blood.

Hypoxia: Deficiency of oxygen delivered to the tissues of the body.


Insomnia: A symptom that describes difficulties falling asleep.

Inspiration (Inspiratory Phase): Inhale; part of breathing cycle when breathing in 

Inspiratory Positive Airway Pressure (IPAP): The pressure that is delivered upon inspiration during Bi-level or BiPAP therapy

Invasive: A medical procedure that involves penetrating the skin or a body cavity.


Mixed Sleep Apnea: Sleep disordered breathing characterized by the presence of a central and obstructive apnea.

Multiple Sleep Latency Test (MSLT): An assessment of excessive daytime sleepiness and narcolepsy.


Narcolepsy: Sleep disorder characterized by excessive sleepiness, cataplexy, sleep paralysis, hallucinations, and the abrupt transition from wakefulness into REM sleep.

Nasal Airflow/ Nasal Ventilation: Measuring inspiratory and expiratory airflow.

Non-supine: Sleeping in any position other than on the back.

Non-Invasive: Medical procedure not involves penetrating the skin or a body cavity.

Non-REM or NREM sleep: Approximately 80% of sleep pertaining to stages 1 to 4.

NSR: Normal sinus rhythm. Refers to they way your heart beats.

NPSG: Nocturnal Polysomnogram, or sleep study.

(#)Number of Awakenings: The number of pages scored as wake after sleep onset.


Obstructive apnea: A respiratory episode where there is a complete cessation of airflow, caused by an obstruction in the upper airway and accompanied by a struggle to breathe. To be defined as an obstructive apnea the episode should last 10 seconds or more.

Oximeter: A device that measure the saturation of oxygen in the blood.

Oxygen Desaturation Index (ODI): The number of events the oxygen content of the blood is reduced 4% or more per hour.


Passover Humidifiers are used in conjunction with an xPAP machine to produce cool moisture, which flows from the xPAP, through a chamber filled with cool water, and to the mask. The purpose of a Passover humidifier is to keep the patient’s nasal passage from becoming dry and sore. A Passover humidifier is not plugged in to an electrical outlet and does not have a heater plate.

Periodic Limb Movement Disorder: Also known as periodic leg movements syndrome. A disorder characterized by periodic episodes of repetitive limb movements occuring during sleep that cause arousal in sleep.

PLM arousal index: The total number of periodic limb movements that cause arousals divided by the total number of hours of sleep.

Polysomnogram (PSG):The “gold standard” for evaluating sleep disorders conducting in a sleep laboratory.

PSGT: Polysomnographic technologist.


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; these sensations are relieved by movement.

REM latency: Latency to REM(dreaming) from sleep onset.

RERAs: Respiratory effort related arousals. Episodes that are not apneas or hypopneas, often related to loud snoring, that generally do not cause a decrease in oxygen saturation.

Respiratory: Any specific comments about respiratory events.

Respiratory Disturbance Index (RDI): Pertains to all respiratory related events per hour measured via portable monitor or PSG.

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; these sensations are relieved by movement.

RPSGT: Registered polysomnographic technologist.


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

Sleep Debt: The accumulated amount of lost sleep resulting from chronic sleep deprivation or insufficient sleep time.

Sleep Deprivation: Insufficient sleep time.

Sleep Disorders: Illnesses during sleep that result in poor sleep quality or dysfunctional sleep.

Sleep efficiency: Total sleep time divided by time in bed (expressed a fraction) or Total sleep time divided by time in bed x 100 (expressed as a percentage)

Sleep latencyTime period measured from bedtime to the beginning of actual sleep.

Sleep onsetTransition from wake to sleep.

Sleep stage shifts: The number of incidents of sleep stage changes.

Snoring intensity: Level of snoring loudness determined by the sleep technologist. Ranging in degrees from mild to very loud snoring.

Soft Palate: The tissues at the rear of the oral cavity consisting of muscular fibers enclosed in a mucous membrane; it closes off the nasal cavity from the oral cavity during swallowing or sucking.

Spontaneous arousal index: The number of spontaneous arousals (e.g. arousals not related to respiratory events, limb movements, snoring, etc) multiplied by the number of hours of sleep.

Stages of Sleep Stage 1: The lightest stage of sleep. Transitional stage from wake. top

Stage 1 shifts: The number of times the sleep stage changed to stage 1.

Stage 2: The first true stage of sleep.

Stages 3/4: The deepest, most restorative sleep.

Sleep stage NREM: Major sleep state apart from REMS; comprises sleep stages 1-4.

Stage REM: The dreaming stage; Normally occurs every 60-90 minutes.

Supine: Sleeping on back.


Tidal Volume: Volume of air that passes in and out of the lungs in an ordinary breath.

Titration: Progressive adjustment of CPAP pressure to achieve an optimum pressures setting to effectively manage a person’s obstructive sleep apnea.

Tonsils: A pair of prominent tissue that are located opposite each other in the throat.

Total arousal index: Total number of all arousals multiplied by the number of hours of sleep.

Total # of PLMs: The number of leg movements in sleep that last greater than 0.5 seconds.


Upper Airway: Part of the respiratory anatomy that includes the nose, nostrils, sinus passages, septum, turbinates; the tongue, jaws, hard and soft palate, muscles of the tongue and throat, etc.

Uvula: The small piece of soft tissue that can be seen dangling down from the soft palate over the back of the tongue.

Uvulopalatopharyngoplasty (UPPP): A surgical procedure performed by an ENT specialist as a alternative treatment option to manage obstructive sleep option.




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