CPAP Glossary Page
CPAP & Sleep Apnea Glossary
Plain-language definitions for the terms you'll come across in your diagnosis, your machine's settings, and your sleep study report.
A
AHI Apnea-Hypopnea Index
The number of breathing pauses (apneas) and partial blockages (hypopneas) per hour of sleep. This single number is what actually defines whether someone has sleep apnea, and how severe it is.
See also: AHI Severity Scale on our Buying GuideApnea
A complete pause in breathing lasting at least 10 seconds during sleep.
APAP Auto-Adjusting Positive Airway Pressure
A CPAP-style machine that continuously adjusts its pressure throughout the night based on your breathing, rather than delivering one fixed pressure all night long.
Adherence also called Compliance
How consistently someone uses their CPAP machine, usually measured in average hours per night and nights per week. Most machines track this automatically.
Auto-Trak ResMed feature name
A ResMed-specific technology that detects your individual breathing pattern and adjusts airflow response accordingly — one of several brand names you'll see for similar auto-adjusting technology.
Aerophagia
Swallowing air during CPAP therapy, which can cause bloating or a gassy feeling. Usually improves by lowering pressure slightly, switching to BiPAP, sleeping on your side, or using a chinstrap to keep the mouth closed.
Anti-Asphyxia Valve AAV
A small safety valve built into some mask elbows, mainly on full-face masks, that opens automatically to let in room air if the machine stops delivering pressure — for example during a power cut. It closes again once therapy air is flowing normally, so you're never fully sealed off from breathing room air.
B
BiPAP Bilevel Positive Airway Pressure
A machine that delivers two separate pressures — a higher one when you inhale, a lower one when you exhale — often more comfortable than a single fixed CPAP pressure, especially at higher settings.
Berlin Questionnaire
A screening questionnaire used to flag someone's likelihood of having obstructive sleep apnea, based on snoring, tiredness, blood pressure, and body weight. Often used alongside or instead of STOP-BANG.
Bolus oxygen therapy
A single "puff" of oxygen released by a pulse dose concentrator right as you inhale, rather than a continuous stream. The size of the bolus (measured in milliliters) increases as the device's dose setting is increased.
C
Central Sleep Apnea (CSA)
A type of sleep apnea where the airway isn't blocked at all — the brain simply stops sending the signal to breathe. Less common than obstructive sleep apnea, and usually not accompanied by loud snoring.
See also: Types of Sleep ApneaComplex Sleep Apnea also called Mixed Sleep Apnea
A combination of obstructive and central sleep apnea occurring in the same person, sometimes only discovered after starting CPAP therapy for what looked like straightforward OSA.
CPAP Continuous Positive Airway Pressure
The most common sleep apnea treatment: a machine that delivers a steady stream of pressurized air through a mask, keeping your airway open all night.
Chinstrap
A strap worn around the jaw and over the top of the head to keep the mouth closed during sleep — commonly used by nasal mask or nasal pillow users who tend to breathe through their mouth, and one of the simplest fixes for aerophagia.
Cushion
The soft part of a mask that actually touches your face and forms the seal — sits inside the harder mask frame. Cushions wear out with regular use and skin oils, so most manufacturers recommend replacing them every few months to maintain a good seal.
COPD Chronic Obstructive Pulmonary Disease
A group of progressive lung conditions that make breathing difficult. COPD is one of the most common reasons someone is prescribed supplemental oxygen therapy, separate from sleep apnea, though the two conditions can co-exist.
Continuous Flow oxygen therapy
An oxygen delivery mode that releases a steady, uninterrupted stream of oxygen at a fixed LPM rate, regardless of your breathing pattern — the traditional method, and generally what's used for oxygen therapy during sleep.
D
Desaturation
A drop in blood oxygen levels, typically caused by a breathing pause. Sleep studies track how often and how far your oxygen levels dip throughout the night.
Data Card also SD Card
The small memory card inside most CPAP machines that records your nightly usage, AHI, and leak rate data — this is what we (or your machine's companion app) read to see how your therapy is actually performing.
Diffuser
A small filter placed at the mask's exhalation port to spread out and quieten the exiting air — mainly a noise-reduction feature for anyone sharing a bed.
Disposable Filter also Ultra-Fine Filter
A thin paper or polyester filter offering finer filtration than a reusable foam filter, but not washable — replace roughly every 30 days, or sooner if it looks discolored. Given local dust conditions in the UAE, we recommend checking weekly rather than waiting the full month.
E
EPR Expiratory Pressure Relief
A comfort feature that slightly lowers pressure right as you exhale, making it feel less like breathing against resistance. Different brands have their own name for a similar feature.
Excessive Daytime Sleepiness (EDS)
Persistent tiredness or drowsiness during the day despite what seems like a full night's sleep — one of the most common symptoms people notice before ever being diagnosed.
Elbow also Swivel
The small angled connector piece that joins your mask to the CPAP tubing, usually able to rotate freely so the hose doesn't drag or twist the mask out of position overnight.
EPAP Expiratory Positive Airway Pressure
The lower of the two pressures delivered by a BiPAP machine, applied while you exhale. Paired with IPAP (the higher inhale pressure), this is what makes BiPAP feel different from a single fixed CPAP pressure.
Exhalation Port also Vent
Small holes built into most masks that continuously release a little air — this is intentional, not a leak, and exists to flush out exhaled carbon dioxide so you don't rebreathe it.
F
Forehead Support also Forehead Pad
A cushioned pad on full-face masks that rests against the forehead, helping distribute pressure evenly so the mask doesn't dig into the bridge of the nose.
Frame
The hard, structural part of a mask that the soft cushion clips into, and that the headgear and elbow attach to.
Full-Face Mask
A mask that covers both the nose and mouth, sealing around the outer edges of the face. Necessary for mouth breathers, chronic nasal congestion, or higher prescribed pressures.
See also: Choosing a MaskFlow Meter oxygen concentrators
The dial or digital display on an oxygen concentrator that shows and controls how much oxygen is being delivered, measured in LPM. Lets you (and us, when checking your setup) confirm it's actually set to your prescribed dose.
H
Headgear
The strap system — usually Velcro or magnetic-clip fastened — that holds your mask in place against your face overnight. Stretches out with use, so most manufacturers recommend replacing it every 6–9 months.
Hypoallergenic Filter also Bacteria Filter
An extra-fine filter, sometimes fitted as a separate in-line add-on, that blocks not just dust and pollen but viruses and bacteria too — worth considering if you're especially prone to allergies or respiratory sensitivity.
Hypoxemia
Lower-than-normal oxygen levels in the blood. Severe or chronic hypoxemia is one of the main reasons a doctor may prescribe supplemental oxygen therapy via an oxygen concentrator.
Humidifier
A water chamber built into most modern CPAP machines that adds moisture to the air before it reaches you, preventing the dry mouth and scratchy throat that dry, pressurized air can cause — especially relevant given how much air conditioning dries out indoor air here in the UAE.
See also: Climate & Humidity Settings for the UAEHypopnea
A partial blockage of the airway during sleep — breathing continues, but airflow is significantly reduced rather than fully stopped.
HSAT Home Sleep Apnea Test
A simplified sleep study done in your own bed rather than an overnight stay in a sleep lab, using a portable device to track breathing, oxygen levels, and heart rate.
See also: WatchPat One Home Sleep TestI
IPAP Inspiratory Positive Airway Pressure
The higher of the two pressures delivered by a BiPAP machine, applied while you inhale. Set higher than EPAP (the exhale pressure) to keep the airway propped open during the harder work of breathing in.
L
Leak Rate
How much air is escaping around your mask seal rather than reaching your airway as intended — most modern machines display this on-screen or in their app. A consistently high leak rate usually means a mask fit or sizing issue.
LPM Liters Per Minute
The standard unit for measuring continuous-flow oxygen output — home concentrators typically range from 1–10 LPM, portable units usually 1–5 LPM. Your prescribed LPM is set by your doctor based on your blood oxygen needs.
LTOT Long-Term Oxygen Therapy
Oxygen therapy used on an ongoing, daily basis (often many hours a day, sometimes continuously) for chronic conditions like COPD, as opposed to short-term or emergency oxygen use.
Loops
A minimal headgear style that hooks behind the ears rather than wrapping fully around the head — a lighter, less bulky alternative for people who find standard headgear too warm or constricting.
M
Micro-arousal
A very brief, partial waking of the brain — often just a few seconds — that happens at the end of each apnea event so breathing can resume. Too brief to remember, but frequent enough to prevent deep, restorative sleep.
Mask Clips also Headgear Clips
The small clips — either standard plastic clips or magnetic clips — that attach the headgear straps to the mask frame. Magnetic clips make putting the mask on and taking it off faster, but must be avoided by anyone with a pacemaker or other active implant.
Membrane valve membrane
The thin flexible disc inside an anti-asphyxia valve that physically opens and closes to let room air in or seal it out. A membrane that's torn, stuck, or missing means the safety valve won't work properly — worth checking if you notice extra noise or air movement around your elbow.
N
Nasal Mask
A mask that covers just the nose. The most commonly used mask type and usually the first one a clinic recommends trying.
See also: Choosing a MaskNasal Cannula oxygen therapy
The thin tube with two small prongs that rests under the nose to deliver oxygen from a concentrator — the standard delivery method for oxygen therapy, distinct from a CPAP mask.
Nasal Pillow Mask
A minimal mask that seals directly at the nostrils rather than covering the whole nose. Lightest and least visually intrusive option, though less ideal at very high pressures.
O
Obstructive Sleep Apnea (OSA)
The most common form of sleep apnea, caused by the soft tissue at the back of the throat relaxing and collapsing during sleep, physically blocking airflow.
See also: Sleep Apnea: What It Is and How Common It IsOximetry
Measurement of blood oxygen saturation, usually via a small sensor clipped to a finger — one of the key readings recorded during a sleep study.
Oral Appliance
A custom-fitted mouthguard-style device, worn during sleep, that repositions the jaw to help keep the airway open — sometimes used for mild OSA or for people who can't tolerate CPAP.
Oxygen Concentrator
A device that draws in ordinary room air and filters out nitrogen, delivering purified oxygen through a nasal cannula or mask — unlike an oxygen tank, it needs no refilling, only electricity. Available as stationary (home) or portable units.
Oxygen Concentration also Purity
The percentage of actual oxygen in the air a concentrator outputs. Medical-grade devices typically deliver 87–96% purity; regular room air, by comparison, is only about 21% oxygen.
Oxygen Conserver
A device or built-in feature that releases oxygen only during inhalation rather than continuously, stretching a limited oxygen supply further — this is essentially what makes pulse dose delivery possible.
P
Polysomnography In-Lab Sleep Study
The most comprehensive sleep test, done overnight in a sleep lab with full monitoring — brain waves, eye movement, breathing, oxygen, and heart rate all recorded at once. The gold standard, usually reserved for more complex cases.
Pressure Titration
The process of finding the exact air pressure setting that best keeps your airway open, either during a lab sleep study or automatically via an APAP machine's own adjustment over several nights.
Pillows Nasal Pillows, mask component
The small, soft silicone or foam inserts that sit directly at the nostrils on a nasal pillow mask, sealing there rather than around the whole nose. Sold as a replaceable part on their own, separate from the full nasal pillow mask assembly.
Pulse Dose also Pulse Flow, oxygen therapy
An oxygen delivery mode that releases a measured "bolus" of oxygen only when it senses you inhaling, rather than a constant stream — common on portable concentrators since it conserves oxygen and battery life. A pulse setting of "2" is not the same as 2 LPM continuous flow; they're different measurement systems entirely.
Port Cap also Port Plug
A small plastic cap that covers the pressure test port on a mask frame — the port a clinician uses to measure your actual delivered pressure during a check-up. Left uncovered, it causes a steady air leak, so make sure it's snapped back in place after any professional pressure check.
R
Ramp Feature
A setting that starts your machine at a lower, gentler pressure and gradually increases it over several minutes, making it easier to fall asleep before full therapy pressure kicks in.
Rainout
Condensation that builds up inside the CPAP tubing, usually when warm humidified air cools down as it travels through a colder tube — common in heavily air-conditioned bedrooms.
See also: Common Issues We See LocallyReusable Filter also Foam Filter
A washable foam filter that traps larger particles like dust and pet dander. Rinse it weekly with warm water, let it fully air dry, and replace it roughly every 6 months — never while still damp.
S
STOP-BANG
A short screening questionnaire used to flag someone's risk of obstructive sleep apnea, based on Snoring, Tiredness, Observed pauses in breathing, blood Pressure, BMI, Age, Neck size, and Gender.
Sleep Architecture
The structure and pattern of sleep stages across a night — how much time is spent in light sleep, deep sleep, and REM sleep, and how that pattern shifts and cycles.
Sleep Latency
How long it takes to fall asleep after lying down. Unusually short sleep latency during the day can be a sign of significant sleep deprivation from conditions like untreated sleep apnea.
Sieve Bed oxygen concentrators
The internal component inside an oxygen concentrator, filled with a mineral called zeolite, that absorbs nitrogen out of ordinary room air so what's left is concentrated oxygen. Most concentrators alternate between two sieve beds so oxygen output stays continuous.
Short Tube
A shorter, often more flexible connector piece — separate from the main CPAP hose — that runs between the mask's elbow and the machine's main tubing on certain mask designs. Not every mask has one; it's mainly a feature on a handful of nasal pillow and full-face styles built for reduced drag near the face.
Swivel
The rotating joint, usually built into the elbow, that lets the tube spin freely without twisting the mask out of position or pulling on your face as you move in your sleep. See also Elbow.
T
Titration Study
A sleep study specifically focused on finding your correct CPAP or BiPAP pressure setting, sometimes done as a second night following an initial diagnostic sleep study.
U
UPPP Uvulopalatopharyngoplasty
A surgical procedure that removes excess tissue from the throat to widen the airway — occasionally considered for OSA when other treatments haven't worked, and typically a later-stage option rather than a first-line treatment.
W
Wide Straps also Comfort Straps
A headgear variant using broader, more padded straps instead of thin elastic — spreads pressure over more surface area, which can reduce marks and irritation, especially for side sleepers or anyone sensitive to standard strap headgear.
Z
Zeolite
The porous, crystal-like mineral packed inside an oxygen concentrator's sieve beds. Its large surface area lets it absorb nitrogen from incoming air very effectively, which is the whole trick behind how a concentrator produces purified oxygen from ordinary room air.
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