CPAP Glossary Page
CPAP & Sleep Apnea Glossary
Plain-language definitions for the terms you'll come across in your diagnosis, your CPAP machine, and your sleep study or sleep report.
A
Adherence also called Compliance
How consistently someone uses their CPAP machine, usually measured using hours of use per night and nights of use. Most modern machines record this information automatically.
AHI Apnea-Hypopnea Index
The average number of apneas and hypopneas recorded per hour of sleep. AHI is one of the primary measurements used to identify and grade the severity of sleep-disordered breathing.
See also: AHI Severity Scale on our Buying GuideAir Filter also Machine Filter
A filter positioned at the air intake of a PAP machine to help reduce dust and other airborne particles entering the device.
Airflow Sensor
A sensor used during a sleep study to detect airflow through the nose and mouth and help identify breathing disturbances.
Airway
The passage through which air travels from the nose and mouth to the lungs. During obstructive sleep apnea, parts of the upper airway can narrow or collapse during sleep.
Anti-Asphyxia Valve AAV
A safety valve built into some CPAP masks that allows room air to enter if normal therapy airflow stops, helping prevent complete blockage of the mask's breathing pathway.
APAP Auto-Adjusting Positive Airway Pressure
A CPAP-style machine that automatically adjusts pressure throughout the night in response to changes in your breathing.
Apnea
A complete pause in breathing lasting at least 10 seconds during sleep.
Arousal
A brief shift in brain activity from sleep toward wakefulness. Arousals may be associated with breathing disturbances, limb movements or other sleep disruptions.
Arousal Index AI
The average number of arousals from sleep per hour of sleep. Arousals can be associated with breathing disturbances, limb movements, noise or other factors and may contribute to fragmented sleep.
ASV Adaptive Servo-Ventilation
A form of non-invasive ventilation that continuously adjusts pressure support in response to a person's breathing pattern. It is used for selected types of central or complex sleep-disordered breathing.
Auto-Trak PAP technology
A technology used in some PAP devices to detect and respond to an individual's breathing pattern. Similar automatic breathing-response technologies may have different names depending on the manufacturer.
AVAPS Average Volume-Assured Pressure Support
A ventilation mode that automatically adjusts pressure support to help maintain a target tidal volume. It is used in certain forms of non-invasive ventilation.
Aerophagia
Swallowing air during CPAP therapy, which can cause bloating, abdominal discomfort or a gassy feeling.
B
Backup Rate Backup Respiratory Rate
A minimum respiratory rate programmed into certain bilevel PAP and ventilatory devices. If spontaneous breathing falls below the set rate, the device can provide supported breaths.
BiPAP Bilevel Positive Airway Pressure
A machine that delivers two pressure levels: a higher pressure during inhalation and a lower pressure during exhalation. It is commonly used when bilevel therapy is prescribed for specific breathing or ventilation needs.
Berlin Questionnaire
A screening questionnaire used to assess the likelihood of obstructive sleep apnea based on factors including snoring, daytime sleepiness, high blood pressure and body weight.
Bolus oxygen therapy
A measured burst of oxygen released by a pulse-dose oxygen concentrator when inhalation is detected.
C
CAI Central Apnea Index
The average number of central apnea events recorded per hour of sleep. Central apneas occur when breathing effort temporarily stops because the normal respiratory drive is reduced or absent.
Cataplexy
A sudden temporary loss of muscle tone, often triggered by strong emotions, that can occur in people with narcolepsy.
Central Apnea
A pause in breathing caused by a temporary reduction or absence of the brain's signal to the muscles responsible for breathing, rather than by a physical blockage of the airway.
Central Sleep Apnea CSA
A type of sleep apnea in which breathing pauses occur because the normal respiratory drive is temporarily reduced or absent. Unlike obstructive sleep apnea, the airway may not be physically blocked during the event.
See also: Types of Sleep ApneaChin EMG Electromyography
Recording of muscle activity from muscles under the chin during polysomnography. Chin EMG helps identify sleep stages and is particularly useful for identifying REM sleep.
Chinstrap
A strap worn around the jaw and head to help reduce mouth opening during sleep, often used with nasal or nasal pillow masks.
Climate Control
An automatic or manual system used with some PAP devices to adjust humidity and temperature for improved comfort during therapy.
Complex Sleep Apnea Treatment-Emergent Central Sleep Apnea
A term historically used when central breathing events become apparent during treatment of obstructive sleep apnea with PAP therapy. Treatment-emergent central sleep apnea is the terminology commonly used in current clinical contexts.
COPD Chronic Obstructive Pulmonary Disease
A group of chronic lung diseases that restrict airflow and make breathing more difficult. COPD and sleep apnea can occur together.
CPAP Continuous Positive Airway Pressure
A common treatment for obstructive sleep apnea in which a machine delivers pressurized air through a mask to help keep the upper airway open during sleep.
CPAP Filter
A replaceable filter used to reduce airborne particles entering a CPAP or PAP machine. Different devices may use disposable, reusable or fine-particle filters.
Continuous Flow oxygen therapy
An oxygen delivery method that provides a continuous stream of oxygen at a prescribed flow rate, generally measured in liters per minute.
Cushion
The soft part of a CPAP mask that contacts the face and creates the seal. Cushions are replaceable components and gradually wear with regular use.
Cycle
The mechanism used by a bilevel PAP or ventilatory device to detect the transition from inhalation to exhalation.
D
Delayed Sleep-Wake Phase Disorder
A circadian rhythm sleep-wake disorder in which a person's natural sleep and wake times occur substantially later than desired or required.
Desaturation
A drop in blood oxygen saturation. During a sleep study, repeated oxygen desaturations may occur alongside breathing disturbances.
Desaturation Index
Another term sometimes used to describe the Oxygen Desaturation Index (ODI), representing the frequency of oxygen desaturation events during a recording.
Diagnostic Sleep Study
A sleep study performed to investigate possible sleep disorders. Depending on the test, it may record breathing, oxygen levels, heart rate, sleep stages, body position, movements and other physiological signals.
Data Card also SD Card
The memory card used in many PAP machines to store therapy information such as usage, pressure, leak and respiratory-event data.
Diffuser
A component used with some CPAP mask vents or accessories to disperse exhaled airflow and potentially reduce perceived noise.
Disposable Filter also Ultra-Fine Filter
A replaceable filter designed to trap smaller airborne particles before air enters the CPAP machine. Replacement intervals vary by manufacturer and environmental conditions.
E
ECG / EKG Electrocardiogram
A recording of the heart's electrical activity. ECG or EKG monitoring during an in-lab sleep study can help track heart rate and rhythm throughout the night.
EEG Electroencephalogram
A recording of electrical brain activity using sensors placed on the scalp. EEG signals are an important part of polysomnography because they help determine whether a person is awake or asleep and identify sleep stages.
Elbow also Swivel
The connector that joins a CPAP mask to the therapy tubing. Many elbows include a swivel connection that allows the tubing to rotate more freely.
EMG Electromyography
A recording of electrical muscle activity. EMG sensors are used during sleep studies to monitor muscle activity and help identify sleep stages and limb movements.
EOG Electrooculogram
A measurement of eye movements recorded during a sleep study. EOG signals help identify REM sleep and assist with sleep-stage scoring.
EPAP Expiratory Positive Airway Pressure
The pressure delivered during exhalation in bilevel PAP therapy. It is generally lower than IPAP.
EPR Expiratory Pressure Relief
A comfort feature available on some PAP machines that reduces pressure slightly during exhalation to make breathing feel more natural.
Epoch
A standardized period of recording used for scoring sleep stages and other events during polysomnography. Sleep studies are commonly scored in 30-second epochs.
Excessive Daytime Sleepiness EDS
Persistent sleepiness or an increased tendency to fall asleep during the daytime despite having an opportunity for sleep. It is a common symptom associated with several sleep disorders.
Exhalation Port also Vent
The openings built into most CPAP masks that intentionally release exhaled air and help prevent carbon dioxide from being rebreathed.
F
Fatigue
A feeling of reduced energy or physical or mental exhaustion. Fatigue is different from sleepiness, although sleep disorders can contribute to both.
FiO₂ Fraction of Inspired Oxygen
The concentration or fraction of oxygen in the gas being inhaled.
Flow Limitation
A reduction or restriction in airflow caused by narrowing of the upper airway. Flow limitation may occur without meeting the criteria for a full apnea or hypopnea.
Flow Limitation Index
A measurement used by some PAP devices to quantify airflow restriction during therapy.
Flow Meter oxygen concentrators
The control and display used on many oxygen concentrators to set and show oxygen flow, usually measured in liters per minute.
Forehead Support also Forehead Pad
A support or cushioned pad found on some CPAP masks that helps stabilize the mask and distribute contact pressure.
Frame
The structural part of a CPAP mask that supports the cushion and connects to components such as the headgear and elbow.
Full-Face Mask
A CPAP mask that covers both the nose and mouth. Full-face masks can be useful for people who breathe through their mouth during sleep or who cannot comfortably maintain nasal breathing.
See also: Choosing a MaskG
Gasping
An abnormal or labored breathing pattern that may occur during respiratory disturbances or awakenings from sleep.
H
Headgear
The strap system that holds a CPAP mask in position during sleep. Headgear can gradually stretch and wear with regular use.
Heated Humidification
The process of adding moisture to PAP airflow using a heated humidifier and water chamber. It can help reduce dryness and irritation for many users.
Heated Tube also Heated Hose
CPAP tubing containing an integrated heating element designed to maintain airflow temperature and help reduce condensation or rainout.
Hypersomnolence
Excessive sleepiness or an increased tendency to fall asleep during the daytime despite apparently adequate sleep opportunity.
Hypoallergenic Filter also Fine Filter
An additional fine filter designed to capture smaller airborne particles such as dust and allergens. The exact filtration performance depends on the specific filter and manufacturer.
Hypopnea
A reduction in airflow during sleep that meets defined scoring criteria for a partial breathing event. Hypopneas are included in the calculation of AHI.
Hypopnea Index HI
The average number of hypopneas recorded per hour of sleep. The hypopnea index contributes to the overall AHI.
Hypoxemia
A lower-than-normal level of oxygen in the blood. Sleep studies and overnight oximetry can help identify periods of reduced oxygen saturation.
Humidifier
A device or integrated water chamber that adds moisture to PAP airflow, helping reduce dryness of the nose, mouth and throat for many users.
See also: Climate & Humidity Settings for the UAEHSAT Home Sleep Apnea Test
A simplified sleep apnea test performed outside a sleep laboratory, often at home, using portable equipment to record signals such as breathing, oxygen saturation and heart rate.
See also: WatchPat One Home Sleep TestI
Idiopathic Hypersomnia
A sleep disorder characterized by excessive daytime sleepiness despite apparently adequate or prolonged sleep. People may also have difficulty becoming fully alert after sleeping.
Inspiratory Time Ti
The amount of time spent during inhalation. Inspiratory time may be monitored or configured on certain bilevel and ventilatory devices.
IPAP Inspiratory Positive Airway Pressure
The pressure delivered during inhalation in bilevel PAP therapy. IPAP is generally higher than EPAP.
iVAPS Intelligent Volume-Assured Pressure Support
A ventilation mode designed to help maintain a target level of ventilation by automatically adjusting pressure support according to changing breathing requirements.
L
Lateral Position
A sleeping position in which a person lies on their side. Sleep studies may record lateral versus supine sleep to identify positional patterns.
Leak Rate
The amount of air escaping from the mask system rather than being intentionally vented. PAP machines may report leak information to help assess mask fit and therapy performance.
LPM Liters Per Minute
The unit commonly used to describe continuous oxygen flow from an oxygen concentrator or other oxygen source.
LTOT Long-Term Oxygen Therapy
Supplemental oxygen therapy prescribed for ongoing use in people with chronic low blood oxygen levels caused by certain medical conditions.
Loops
A minimal headgear design used on some masks that uses straps or loops around the ears or sides of the head.
Lights Off / Lights Out
The recorded time when the sleep study begins and the person is instructed to attempt to sleep.
Lights On
The recorded time when a sleep recording ends and the person is instructed to wake.
M
Maintenance of Wakefulness Test MWT
A daytime test that evaluates a person's ability to remain awake in a quiet environment. It may be used to assess daytime alertness or treatment effectiveness.
Mask Clips also Headgear Clips
The clips or fasteners used to attach CPAP headgear straps to the mask frame. Some masks use magnetic clips while others use conventional clips.
Mask Fit
How well a CPAP mask sits against the face and maintains an effective seal without excessive unintended air leakage.
Mask Frame
The structural portion of a CPAP mask that supports the cushion and connects the mask components.
Mask Liner
A soft fabric or other interface placed between the mask cushion and skin to improve comfort and may help reduce irritation or minor leaks.
Mask Seal
The contact between the mask cushion and the user's face that helps prevent excessive unintended air leakage during PAP therapy.
Membrane valve membrane
A flexible component inside some mask safety valves that moves to allow room air through when the valve opens.
Micro-arousal
A brief shift from deeper sleep toward lighter sleep or wakefulness. Arousals can be associated with respiratory events, limb movements and other disturbances and may contribute to fragmented sleep.
Minute Ventilation MV
The total volume of air moved into or out of the lungs in one minute. It is calculated from tidal volume and respiratory rate.
Mixed Apnea
An apnea event that contains both central and obstructive characteristics, with a period of absent respiratory effort followed by continued effort against an obstructed airway.
MSLT Multiple Sleep Latency Test
A daytime sleep test that measures how quickly a person falls asleep during a series of scheduled nap opportunities. It is commonly used when evaluating excessive daytime sleepiness and certain disorders such as narcolepsy.
N
N1 Sleep Stage N1
The lightest stage of non-REM sleep and the transition from wakefulness into sleep. N1 normally represents a relatively small portion of total sleep time.
N2 Sleep Stage N2
The second stage of non-REM sleep and usually the largest portion of normal adult sleep. It is deeper than N1 and has characteristic patterns such as sleep spindles and K-complexes.
N3 Sleep Slow-Wave Sleep / Deep Sleep
The deepest stage of non-REM sleep. N3 is associated with slow brain-wave activity and is commonly referred to as deep or slow-wave sleep.
Nasal Cannula oxygen therapy
A lightweight tube with two small prongs positioned near the nostrils to deliver supplemental oxygen from an oxygen source.
Nasal Mask
A CPAP mask that covers the nose and delivers therapy airflow through the nasal passages.
See also: Choosing a MaskNasal Pillow Mask
A minimal CPAP mask that uses small cushions positioned at or around the nostrils, providing less facial coverage than most nasal and full-face masks.
Nasal Pressure Signal
A breathing signal commonly recorded during a sleep study using a nasal cannula or pressure sensor. It helps detect changes in airflow and respiratory events.
NIPPV Non-Invasive Positive Pressure Ventilation
Positive-pressure respiratory support delivered without an invasive airway such as an endotracheal tube.
NIV Non-Invasive Ventilation
Breathing support delivered through a mask or other non-invasive interface rather than an invasive airway.
Nocturnal Hypoxemia
Low blood oxygen levels occurring during sleep. It may be associated with sleep-disordered breathing or other respiratory and medical conditions.
NREM Sleep Non-Rapid Eye Movement Sleep
Sleep consisting of stages N1, N2 and N3. NREM sleep alternates with REM sleep throughout a normal night.
O
OAI Obstructive Apnea Index
The average number of obstructive apnea events recorded per hour of sleep. It is one of the measurements that can be reported separately from the overall AHI.
Obesity Hypoventilation Syndrome OHS
A condition involving obesity and chronic under-ventilation that results in elevated carbon dioxide levels and cannot be explained by another primary cause.
Obstructive Sleep Apnea OSA
The most common form of sleep apnea, caused by repeated narrowing or blockage of the upper airway during sleep, resulting in reduced or interrupted airflow.
See also: Sleep Apnea: What It Is and How Common It IsODI Oxygen Desaturation Index
The average number of oxygen desaturation events recorded per hour. Sleep reports may specify the oxygen drop used to define an event, such as ODI-3% or ODI-4%.
Oral Appliance
A dental device worn during sleep that is designed to modify the position of the jaw or tongue and help maintain a more open upper airway. Oral appliances may be prescribed for selected people with obstructive sleep apnea.
Oximetry
Measurement of blood oxygen saturation, usually using a pulse oximeter placed on a finger. Overnight oximetry can help identify patterns of oxygen desaturation.
Oxygen Concentration also Purity
The percentage of oxygen contained in the gas produced by an oxygen concentrator. The exact output depends on the device, flow setting, operating conditions and manufacturer specifications.
Oxygen Concentrator
A device that takes in room air and concentrates oxygen for delivery to a user through a nasal cannula or other prescribed interface.
Oxygen Conserver
A device or feature that delivers oxygen in response to inhalation rather than continuously, helping conserve the available oxygen supply.
Oxygen Flow
The rate at which oxygen is delivered, generally expressed in liters per minute for continuous-flow oxygen systems.
Oxygen Nadir
The lowest blood oxygen saturation level recorded during a sleep study or overnight oximetry recording. It is commonly reported as the lowest SpO₂ percentage reached during the test.
Oxygen Outlet
The port on an oxygen concentrator through which concentrated oxygen exits the device for delivery to the user.
Oxygen Sensor
A component used by some oxygen concentrators to monitor the oxygen concentration produced by the device.
Oxygen Tubing
Flexible tubing used to deliver oxygen from an oxygen concentrator or other oxygen source to a nasal cannula or other prescribed interface.
P
PAP Positive Airway Pressure
A general term covering therapies such as CPAP, APAP and bilevel PAP that use positive airway pressure to support breathing during sleep.
Periodic Breathing
A repeated pattern of changing breathing intensity that may include periods of deeper breathing alternating with reduced or absent breathing. Some sleep reports and PAP devices record the amount of time spent in periodic breathing.
Periodic Limb Movement Disorder PLMD
A sleep disorder involving repetitive limb movements during sleep that are associated with clinically significant sleep disturbance or daytime impairment.
PLMI Periodic Limb Movement Index
The average number of periodic limb movements recorded per hour of sleep. PLMI is a separate measurement from AHI because it evaluates limb movements rather than breathing events.
PLMS Periodic Limb Movements of Sleep
Repetitive movements of the legs or, less commonly, the arms that occur during sleep. A sleep study can detect and count these movements and determine whether they are associated with arousals.
Polysomnography PSG / In-Lab Sleep Study
A comprehensive overnight sleep study that records multiple physiological signals, which may include brain activity, eye movements, muscle activity, heart rate, breathing, oxygen saturation and body position. It is commonly performed in a sleep laboratory.
Positional Sleep Apnea
Sleep apnea that varies substantially according to body position, particularly between sleeping on the back and sleeping in other positions.
PEEP Positive End-Expiratory Pressure
Pressure maintained in the airway at the end of exhalation. PEEP is commonly used in ventilatory support and is different from the pressure settings used in ordinary CPAP therapy.
Pillows Nasal Pillows, mask component
The small soft cushions used on nasal pillow masks to create a seal around the nostrils. They are commonly available as replaceable mask components.
Port Cap also Port Plug
A small cap used to close a pressure measurement port on certain CPAP masks. If the port is left open, it can create an unintended air leak.
Pressure
The level of positive airway pressure delivered by a PAP machine, generally measured in cmH₂O.
Pressure Range
The minimum and maximum pressure settings available to an auto-adjusting PAP machine.
Pressure Support PS
The difference between inspiratory and expiratory pressure in bilevel ventilation. Pressure support assists breathing during inhalation.
Pressure Titration
The process of determining an appropriate PAP pressure or range of pressures to control breathing disturbances while maintaining comfortable therapy.
Pulse Dose also Pulse Flow, oxygen therapy
An oxygen delivery mode that releases a measured amount of oxygen when inhalation is detected rather than providing a continuous flow. Pulse-dose settings should not be confused with continuous-flow LPM settings.
Portable Oxygen Concentrator POC
A smaller oxygen concentrator designed for mobility and travel. Depending on the model, a portable oxygen concentrator may provide continuous flow, pulse-dose oxygen or both.
PSA Pressure Swing Adsorption
The process used by many oxygen concentrators to separate nitrogen from room air and produce oxygen-enriched gas.
R
Rainout
Condensation that forms inside CPAP tubing when warm humidified air cools. Heated tubing and appropriate humidity settings can help reduce rainout.
See also: Common Issues We See LocallyRamp Feature
A PAP setting that begins therapy at a lower pressure and gradually increases toward the prescribed treatment pressure, making it easier for some users to fall asleep.
RDI Respiratory Disturbance Index
The average number of respiratory disturbances recorded per hour of sleep. Depending on the scoring method, RDI may include apneas, hypopneas and respiratory effort-related arousals (RERAs), so it can be higher than AHI.
REM AHI
The apnea-hypopnea index calculated specifically during periods of REM sleep. Some people experience more breathing disturbances during REM sleep than during other sleep stages.
REM Latency
The amount of time between sleep onset and the first recorded period of REM sleep. It is one of the timing measurements that may appear on a detailed polysomnography report.
REM Sleep Rapid Eye Movement Sleep
A distinct stage of sleep associated with rapid eye movements, characteristic brain activity, vivid dreaming and changes in muscle activity and breathing.
REM Sleep Behavior Disorder RBD
A sleep disorder in which the normal muscle paralysis of REM sleep is reduced or absent, allowing a person to physically act out dreams.
Respiratory Effort Belt
A sensor placed around the chest and/or abdomen during a sleep study to measure respiratory movement and breathing effort.
Respiratory Effort-Related Arousal RERA
A breathing event involving increased respiratory effort and airflow limitation that ends with an arousal from sleep but does not meet the scoring criteria for an apnea or hypopnea.
Respiratory Event Index REI
The average number of respiratory events recorded per hour during a sleep apnea test. REI is commonly reported in home sleep apnea testing, where actual sleep time may not be directly measured.
Respiratory Rate RR
The number of breaths taken per minute. Respiratory rate may be recorded during sleep studies and monitored by some PAP and ventilatory devices.
Reusable Filter also Foam Filter
A washable filter used in some CPAP machines to capture larger airborne particles. Follow the manufacturer's instructions for cleaning and replacement.
Rise Time
The time required for a bilevel device to increase pressure from EPAP toward IPAP during inhalation. Rise-time settings are available on some bilevel and ventilatory devices.
RIP Respiratory Inductance Plethysmography
A method of measuring changes in chest and abdominal movement associated with breathing during a sleep study.
S
S Mode Spontaneous Mode
A bilevel mode in which the device responds to the user's spontaneous inhalation and exhalation rather than using a fixed timed breathing pattern.
Sleep Architecture
The structure and pattern of sleep across a night, including the amount of time spent in N1, N2, N3 and REM sleep and how those stages cycle throughout the night.
Sleep Continuity
How consistently sleep is maintained without repeated awakenings or interruptions.
Sleep Debt
The accumulated difference between the amount of sleep a person needs and the amount of sleep they actually obtain.
Sleep Efficiency
The percentage of the relevant sleep period that was actually spent asleep. It is generally calculated by comparing total sleep time with the amount of time spent in bed or the applicable sleep period.
Sleep Fragmentation
Repeated interruptions or disruptions of sleep that prevent sleep from remaining continuous. Breathing events, arousals, limb movements and environmental factors can contribute to fragmented sleep.
Sleep Hygiene
Habits and environmental practices that support healthy and consistent sleep, such as maintaining a regular sleep schedule and creating a suitable sleep environment.
Sleep Latency
The amount of time it takes to fall asleep after the beginning of the sleep period. It is commonly reported in minutes on sleep-study reports.
Sleep Maintenance Insomnia
Difficulty staying asleep or repeated awakenings during the night.
Sleep Onset Insomnia
Difficulty falling asleep at the beginning of the sleep period.
Sleep Onset Latency SOL / Sleep Latency
The amount of time between the beginning of the sleep period and the first recorded period of sleep. It is one of the standard sleep-timing measurements used in polysomnography.
Sleep Paralysis
A temporary inability to move or speak when falling asleep or waking up. It can occur independently or in association with certain sleep disorders.
Sleep Period Time SPT
The amount of time from sleep onset until final awakening during the sleep period being analyzed.
Sleep-Related Bruxism
Repeated grinding or clenching of the teeth during sleep.
Sleep-Related Hypoventilation
A condition in which breathing during sleep is insufficient to maintain normal ventilation and may result in elevated carbon dioxide levels.
Sleep-Related Hypoxemia
Reduced oxygen levels occurring during sleep that may occur with or without sleep apnea.
Sleep Stage Distribution
The percentage or amount of total sleep spent in each sleep stage, typically reported as N1, N2, N3 and REM.
Sleep Terrors Night Terrors
Episodes of intense fear, screaming or other behaviors arising from sleep, usually during NREM sleep.
Sleep-Wake Cycle
The recurring pattern of sleep and wakefulness across approximately 24 hours, regulated by the body's biological clock and environmental cues.
Shift Work Sleep Disorder
A sleep disorder involving sleep problems or excessive sleepiness associated with work schedules that conflict with the normal sleep-wake cycle.
Sieve Bed oxygen concentrators
An internal component of an oxygen concentrator containing a molecular sieve material that selectively removes nitrogen from incoming air to concentrate oxygen.
Snoring Index
A measurement describing the frequency or amount of snoring detected during a sleep study. The exact calculation can vary between sleep laboratories and devices.
SpO₂ Peripheral Oxygen Saturation
A measurement of the percentage of hemoglobin carrying oxygen in the blood, usually measured by a pulse oximeter. Sleep studies commonly record SpO₂ continuously during the night.
Split-Night Study
A sleep study in which the first part of the night is used for diagnostic assessment and, when appropriate, the remaining portion is used for PAP titration.
ST Mode Spontaneous/Timed Mode
A bilevel ventilation mode that can provide spontaneous breathing support while also using a backup rate when necessary.
STOP-BANG
A screening questionnaire used to assess the risk of obstructive sleep apnea. The name comes from Snoring, Tiredness, Observed apneas, high blood Pressure, BMI, Age, Neck circumference and Gender.
Supine AHI
The apnea-hypopnea index measured specifically while sleeping on the back. Some people experience more obstructive breathing events in the supine position.
Supine Position
A sleeping position in which a person lies on their back.
Supine Sleep
Sleep while lying on the back. Body position is commonly recorded during an in-lab sleep study and may help identify positional patterns in sleep apnea.
Swivel
A rotating connector, often incorporated into a CPAP mask elbow, that allows tubing to move more freely without pulling the mask out of position.
T
T90 Time Below 90% Oxygen Saturation
The amount or percentage of recording time spent with blood oxygen saturation below 90%. T90 is commonly reported when evaluating overnight oxygen levels.
TECSA Treatment-Emergent Central Sleep Apnea
Central apneas that emerge or become prominent after PAP treatment is initiated for obstructive sleep apnea.
Thermistor Airflow Sensor
A temperature-sensitive sensor placed near the nose and mouth during some sleep studies to detect airflow by measuring changes in temperature as air moves in and out.
Tidal Volume VT / Vt
The amount of air moved into or out of the lungs with each breath. Tidal volume is an important measurement in ventilatory support.
Timed Mode
A ventilation mode in which breaths are delivered according to a programmed respiratory rate rather than relying entirely on spontaneous breathing.
TIB Time in Bed
The amount of time spent in bed during the sleep period being analyzed. TIB can include periods when a person is awake before falling asleep or after waking.
Titration Study
A sleep study focused on determining appropriate PAP pressure settings to control breathing disturbances while maintaining comfortable therapy.
TRT Total Recording Time
The total length of time a sleep-study device records its available physiological signals. In home sleep apnea testing, TRT may be used when actual sleep time cannot be measured directly.
TST Total Sleep Time
The total amount of time actually spent asleep during the recorded sleep period. TST differs from total recording time because it excludes periods when the person was awake.
Trigger
The mechanism by which a PAP or ventilator detects the beginning of an inhalation.
U
Upper Airway
The part of the respiratory system extending from the nose and mouth through the throat toward the lower airway. Obstruction of the upper airway during sleep is a key feature of obstructive sleep apnea.
Upper Airway Resistance Syndrome UARS
A sleep-related breathing disorder involving increased resistance to airflow through the upper airway, often associated with flow limitation and respiratory effort-related arousals.
UPPP Uvulopalatopharyngoplasty
A surgical procedure that removes or reshapes selected tissues in the throat to enlarge the upper airway. It may be considered for selected people with obstructive sleep apnea.
V
Ventilation
The movement of air into and out of the lungs. Adequate ventilation is necessary to remove carbon dioxide and support normal gas exchange.
Ventilator
A medical device that provides mechanical assistance to support breathing when a person cannot adequately maintain ventilation independently.
Volume-Assured Pressure Support VAPS
A ventilation approach in which pressure support is automatically adjusted to help achieve a target level of ventilation or tidal volume.
VT / Vt Tidal Volume
The amount of air moved into or out of the lungs with each breath.
W
Wake After Sleep Onset WASO
The total amount of time spent awake after initially falling asleep. WASO is an important measurement of sleep continuity and fragmentation on detailed sleep reports.
Wakefulness
A state of being awake and alert, distinguished from the various stages of sleep.
Wide Straps also Comfort Straps
A headgear design using wider straps to distribute pressure over a larger area and potentially reduce pressure points or skin marks.
Z
Zeolite
A mineral used in the molecular sieve beds of many oxygen concentrators. It selectively adsorbs nitrogen from room air, allowing the device to produce concentrated oxygen.
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