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Category:CPAP Definitions

CPAP Defined

These are common terms that people often need more information about. Articles can be linked to the term definitions which you are now viewing.

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The Terms listed and defined here are those you need for a PSG (Sleep) Study. The terms that follow the list, are varios Sleep Apnea and CPAP terms.

View the original archived CPAP Defined from the CPAPtalk Forum.


Aerophagia is the swallowing of air, whether deliberately (as in to stimulate belching), accidentally, or involuntarily (as a result of anxiety/nervousness). (Note: The correct term for air in the digestive system due to the use of CPAP or ventilators is "gastric insufflation". However, the use of the term "aerophagia" is so ingrained in this forum that it is accepted as correct. When speaking with medical professionals, you should remember to say "gastric insufflation".)

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

An AutoPAP can be set to deliver a range of low/high pressures, customizable within 4 - 20 cm H2O. Learn more here



BR Arousal index: The number of breathing related arousals(apnea, hypopnea, snoring & RERAs) divided by the # hours of sleep.

Bruxism: Grinding of the teeth.


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


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).


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


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

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.


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.

PLMs: Periodic limb movements.

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

Pressure Support The difference between EPAP and IPAP on a bilevel machine.

PS see 'Pressure Support'.

PSGT: Polysomnographic technologist.


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.

ResScan: Software provided by ResMed for use with their various flow generators (cpap machines).

RPSGT: Registered polysomnographic technologist.


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 latency: The first 30 seconds (one `epoch' of recording time) of sleep.

Sleep onset: The first 90 seconds (3 `epochs) of uninterrupted 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.

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

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

Supine: Sleeping on back.


Time in bed: The time in the study from `Lights Out' to `Lights On'.

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

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