CPAP and sleep apnea glossary

Aerophagia is swallowing air, which on CPAP can cause bloating, belching or stomach discomfort in the morning. It is more often reported at higher pressures and in people who breathe through the mouth.

AHI is the number of apneas plus hypopneas per hour. A sleep study measures it per hour of sleep; a CPAP machine estimates it per hour the mask was on. Diagnostic bands for adults are under 5 normal, 5 to under 15 mild, 15 to under 30 moderate, and 30 or more severe.

The AASM is the US professional society for sleep medicine. It publishes the scoring manual that sleep labs use to define apneas, hypopneas, arousals and RERAs, and it accredits sleep centres.

APAP is CPAP that adjusts its pressure through the night within a minimum and maximum your clinician sets. It raises pressure when it detects flow limitation, snoring or apneas, and lowers it when breathing is stable. ResMed calls its algorithm AutoSet.

An apnea is a near-complete stop in breathing. The AASM scores one when airflow falls by 90 percent or more from baseline for at least 10 seconds. Apneas are classed as obstructive, central or mixed by what the breathing effort was doing.

Apple Health is the health data store on iPhone. With your permission, the Apnealytics iPhone and iPad app reads daily summaries such as resting heart rate, HRV, SpO₂, sleep hours and weight and shows them beside your therapy. Only daily summaries leave the device.

An arousal is a brief shift toward wakefulness, seen in a sleep study as a sudden change in brain-wave frequency lasting at least 3 seconds. You usually do not remember it. Arousals can end apneas, hypopneas and RERAs.

ASV is a specialised bilevel therapy for central sleep apnea and Cheyne-Stokes breathing. It varies pressure support breath by breath to stabilise breathing and can deliver backup breaths. It is contraindicated in some people with heart failure with reduced ejection fraction, so it is prescribed only after a cardiac review.

The Berlin questionnaire is a 10-item sleep apnea screener grouped into three categories: snoring and witnessed pauses, daytime sleepiness, and high blood pressure or a BMI over 30. Two or more positive categories means high risk. It was published by Netzer and colleagues in 1999.

Bilevel therapy uses two pressures: a higher one while you breathe in (IPAP) and a lower one while you breathe out (EPAP). The gap between them is pressure support. It is used when someone needs high pressures, struggles to exhale against CPAP, or has certain breathing or lung conditions.

BYOK means you connect your own OpenAI or Anthropic API key to use Ask your data, the feature that lets you chat with your therapy history. Access is read-only and scoped to your own account.

Card-to-Cloud is a ResMed AirView service that lets a clinic or equipment supplier upload the data from a machine's SD card into AirView when the machine has no working modem. It sends data to your provider's system, not to you.

CBT-I is a structured, non-drug treatment for chronic insomnia. It combines sleep scheduling, stimulus control, work on unhelpful thoughts about sleep, and sleep hygiene, usually over four to eight sessions. The American College of Physicians recommends it as first-line treatment for chronic insomnia in adults (2016).

A central apnea is a pause in breathing with no breathing effort: the airway is open, but the brain does not send the signal to breathe. ResMed machines detect it by sending small pressure pulses and checking whether the airway is open, and label it "clear airway".

Cheyne-Stokes respiration is a waxing and waning breathing pattern with central apneas or hypopneas between the crescendo-decrescendo cycles. It is seen most often with heart failure, after a stroke, or at high altitude. Some ResMed machines flag suspected periods of it.

A chin strap is a soft band that holds the jaw closed while you sleep. It is used with nasal masks and nasal pillows to reduce air escaping through the mouth.

cmH₂O is the unit CPAP pressure is measured in: the pressure needed to push a column of water up by one centimetre. One cmH₂O is about 0.98 hectopascals. Most CPAP machines work in a range of 4 to 20 cmH₂O.

COMISA is the term for having both insomnia and obstructive sleep apnea at the same time. It is common, and people with both tend to find CPAP harder to use consistently.

Compliance is whether you use CPAP enough to meet your insurer's rule. Under the US Medicare rule, that means 4 or more hours a night on at least 70 percent of nights (21 of 30) in any consecutive 30-day window within the first 90 days. Many private insurers use similar rules.

Compliance autopilot is the Apnealytics feature that scans your nights, finds a qualifying 30-day window automatically, and drafts a compliance letter. It is part of Pro reports.

CPAP is the standard treatment for obstructive sleep apnea. A machine blows air through a tube and mask at a steady pressure that splints the airway open so it cannot collapse. "CPAP" is also used loosely for the machine itself and for auto-adjusting machines.

CPAP-Check is a mode on some Philips machines, including DreamStation, that starts at a fixed pressure and adjusts it gradually over time within a small range around that pressure, based on your recent breathing.

The cushion is the soft silicone or foam part of the mask that touches your face and makes the seal. Cushions wear out with skin oils and cleaning and are replaced on a schedule, often monthly for nasal and full face cushions.

DATALOG is the folder on a ResMed SD card that holds the detailed night files, with one subfolder per date. Inside are EDF files for high-resolution breathing and pressure, lower-resolution trend signals, events, and oximetry if connected.

A desaturation is a drop in blood oxygen saturation (SpO₂) from your baseline, usually counted when it falls by 3 or 4 percentage points. Breathing events often cause one, with a short delay.

A DME is the company that supplies your CPAP machine, mask and resupplies, often on your insurer's behalf. In the US it is usually the DME that checks your compliance in the first 90 days.

EDF is an open file format for recording physiological signals over time. ResMed machines and many oximeters save their data as.edf files.

EPAP is the lower pressure a bilevel machine delivers while you breathe out. It is the pressure mainly responsible for keeping the airway open against collapse.

EPR is a ResMed comfort setting that lowers pressure slightly as you breathe out, by 1, 2 or 3 cmH₂O. It makes exhaling feel easier without switching to a bilevel machine.

The ESS asks how likely you are to doze in eight everyday situations, each scored 0 to 3, for a total of 0 to 24. A total above 10 is generally read as excessive daytime sleepiness. It was published by Dr Murray Johns in 1991 and is licensed.

Flow limitation is a flattening of the breath's airflow shape as you breathe in: the airway narrows enough to cap airflow without fully closing. ResMed machines report it as an index from 0 to 1.

A full face mask covers both nose and mouth. Traditional designs sit over the bridge of the nose; under-nose (hybrid) designs seal under the nose and around the mouth.

A Heads up alert is a plain-language note on your dashboard when a night is unusual for you, for example "AHI 8.5 — 2.9× your usual ~3.0". It compares the night against your own baseline rather than a fixed number.

Health Connect is Android's on-device health data store. With your permission, the Apnealytics Android app reads daily summaries such as resting heart rate, HRV, SpO₂, sleep hours and weight and shows them beside your therapy.

An HSAT is a simplified sleep study you wear at home, usually recording airflow, breathing effort, oximetry and position. It cannot see sleep stages, so it reports events per hour of recording time (often called REI) rather than per hour of sleep.

HRV is the variation in time between heartbeats. Apple Health reports it as SDNN, in milliseconds; Health Connect may report a different measure. Higher values usually reflect a more relaxed nervous system, but HRV varies widely between people.

A humidifier warms and moistens the air from your CPAP using a small water tank on a heated plate. A heated tube (such as ResMed ClimateLine) is a hose with a built-in wire that keeps the air warm on its way to the mask.

A hypopnea is a partial reduction in breathing. The AASM's recommended rule scores one when airflow falls by at least 30 percent for at least 10 seconds with either a 3 percent oxygen drop or an arousal. An alternative rule, used by US Medicare, requires a 4 percent drop.

The ISI is a seven-item questionnaire about insomnia over the past two weeks, scored 0 to 28. Bands are 0–7 no clinically significant insomnia, 8–14 subthreshold, 15–21 moderate and 22–28 severe. It was developed by Charles Morin and is licensed.

IPAP is the higher pressure a bilevel machine delivers while you breathe in. IPAP minus EPAP equals pressure support.

Large leak is time spent with leak above the manufacturer's threshold, the point where the machine can no longer measure breathing reliably. ResMed reports it as time or percent of the night.

Leak rate is the flow of air escaping from the system, in litres per minute. ResMed reports unintentional leak, after subtracting the mask's designed vent flow; Philips reports total leak, including the vent. Apnealytics shows leak P95 for each night.

Mask Analytics groups your nights by the mask you used and shows seal, AHI and usage for each one. It reads which mask you were on from your gear history.

Mask pressure is the pressure measured or estimated at the mask, as opposed to the pressure set on the machine. ResMed records it as a signal in the night's detailed files.

Minute ventilation is the volume of air you breathe in one minute, in litres. It equals tidal volume multiplied by respiratory rate; a resting adult is usually around 5 to 8 L/min.

A mixed apnea starts as a central apnea, with no breathing effort, and ends as an obstructive one, with effort against a closed airway. In a sleep study it is usually counted with obstructive events.

Many recent CPAP machines, including the ResMed AirSense 10 and 11, have a built-in cellular modem that sends nightly summary data to the manufacturer's cloud for your provider and the manufacturer's app. Detailed breath-by-breath data stays on the SD card.

Mouth breathing on CPAP means air escapes through an open mouth, most often with a nasal mask or nasal pillows. It causes dry mouth, noise and high leak.

myAir is ResMed's free app and website for its own machines. It shows a single 0–100 score each night built from usage, mask seal, events and mask on/off, using data sent by the machine's modem.

A nasal mask covers the nose with a triangular cushion, sealing over the bridge or, in cradle designs, under the nose. It does not cover the mouth.

Nasal pillows are small soft cushions that sit at the entrance of the nostrils. They are the most minimal mask type.

The NoSAS score is a sleep apnea screener built from neck size, BMI, snoring, age and sex, scored 0 to 17. A score of 8 or more indicates a higher likelihood of clinically significant sleep-disordered breathing. It was published by Marti-Soler and colleagues in 2016.

The NOSE scale is a five-item questionnaire about nasal blockage over the past month. Each item is scored 0 to 4 and the total is multiplied by 5 to give 0 to 100; higher means worse obstruction. It was published by Stewart and colleagues in 2004.

An obstructive apnea is a pause in airflow of 10 seconds or more while you keep trying to breathe: the airway has collapsed. It is the defining event of obstructive sleep apnea.

ODI is the number of oxygen desaturations per hour. ODI₃ counts drops of 3 percent or more from baseline; ODI₄ counts drops of 4 percent or more, so ODI₄ is always equal to or lower than ODI₃. It needs an oximeter.

OSA is a condition in which the upper airway repeatedly narrows or closes during sleep, causing apneas, hypopneas, oxygen drops and broken sleep. It is diagnosed with a sleep study and graded by AHI.

OSCAR is free, open-source desktop software for Windows, Mac and Linux that reads data from ResMed, Philips, Fisher & Paykel, Löwenstein and other machines. It is detailed and powerful, with a steep learning curve and no phone or cloud version.

An oximeter is a fingertip, ring or wrist sensor that measures blood oxygen saturation (SpO₂) and pulse using light. Overnight models record all night and export a file.

P95 pressure is the pressure your machine stayed at or below for 95 percent of the night. On APAP it describes the top of what you needed, ignoring brief spikes.

The pressure range is the minimum and maximum pressure an APAP or auto-bilevel machine is allowed to use. Your clinician sets it from your sleep study, titration or trial data.

Pressure support is the difference between IPAP and EPAP on a bilevel machine. More pressure support means more help moving air in on each breath.

PSG is a full overnight sleep study in a lab, recording brain waves (EEG), eye movement, muscle tone, heart rhythm, airflow, breathing effort, oxygen and position. A technologist scores it against AASM rules.

Rainout is condensation that forms in the tube or mask when warm, humid air cools on its way to you. You may hear gurgling or feel drops of water.

Ramp starts the night at a lower pressure and raises it to your therapy pressure over a set time, so falling asleep feels easier. ResMed's AutoRamp waits until it detects that you are asleep before rising.

RDI is the number of apneas, hypopneas and RERAs per hour of sleep. It is always equal to or higher than AHI, because it adds RERAs.

A RERA is a series of breaths lasting at least 10 seconds with increasing effort or flattening of airflow that ends in an arousal, without meeting the rules for an apnea or hypopnea. It is scored in a sleep study.

Residual AHI is the AHI that remains while you are on treatment, as estimated by your CPAP machine. It is not graded with the diagnostic mild, moderate and severe bands; the common target is under 5.

Respiratory rate is the number of breaths per minute. Typical adult values at rest are about 12 to 20. ResMed machines report it from the flow signal, and Apnealytics shows it on the dashboard.

Resting heart rate is your heart rate at rest, usually reported once a day by a watch or ring. Apnealytics reads it from Apple Health or Health Connect.

The SCI is an eight-item questionnaire about sleep over the past month, scored 0 to 32, where higher is better. A score of 16 or less suggests probable insomnia disorder. It was published by Espie and colleagues in 2014.

The SD card is the small memory card in many CPAP machines, including ResMed AirSense, AirCurve and S9, Philips DreamStation and Fisher & Paykel SleepStyle. It stores the full detail of every night. The ResMed AirMini has no SD card.

A share link is a private, read-only web link that shows a clinician your aggregate therapy data. It is tokenized, not indexed by search engines, excludes health identifiers by default, and you can revoke it at any time (Pro).

Sleep efficiency is total sleep time divided by time in bed, as a percentage. Around 85 percent or higher is generally considered good for adults.

Sleep latency is how long it takes to fall asleep after lights out. In a sleep study it is measured from EEG.

The Sleep Score is Apnealytics' 0–100 summary of a CPAP night, built from your AHI, usage hours and leak. The three component scores sit beneath the total so you can see which one moved.

A sleep study is any test that records breathing during sleep to diagnose a sleep disorder. It may be a full in-lab PSG, a home sleep apnea test, or a titration study to set pressure.

Snoring is the sound of vibrating tissue in a narrowed upper airway. On CPAP, some ResMed machines detect it from the flow signal and APAP uses it as a cue to raise pressure.

SpO₂ is the percentage of haemoglobin carrying oxygen, measured with light by a pulse oximeter. Healthy values at rest are usually 95 to 100 percent; brief overnight dips are normal.

STOP-Bang is an eight-question yes/no sleep apnea screener: snoring, tiredness, observed pauses, high blood pressure, BMI over 35, age over 50, neck circumference over 40 cm, and male sex. Scores of 0–2 are low risk, 3–4 intermediate and 5–8 high. It was published by Chung and colleagues in 2008.

STR.edf is the summary file at the top of a ResMed SD card. It holds one record per day with usage, AHI, leak, pressure statistics and settings.

T90 is the time spent with oxygen saturation below 90 percent, shown as minutes or as a percentage of the recording. It needs an oximeter.

TECSA is central sleep apnea that appears or persists once obstructive events are treated with CPAP. In many people it settles over the first weeks to months of therapy.

A therapy score is a single number that summarises a CPAP night. ResMed's myAir score and the Apnealytics Sleep Score are examples, and each is calculated differently.

Tidal volume is the volume of air in a single breath, in millilitres. A resting adult is often around 400 to 600 mL. ResMed machines estimate it from the flow signal.

A titration study is a sleep lab night where a technologist adjusts CPAP or bilevel pressure to find the level that controls your events. A split-night study does diagnosis and titration on the same night.

UARS describes sleep disrupted by repeated RERAs and flow limitation, with an AHI that may be under 5. Current international classification groups it within obstructive sleep apnea rather than as a separate diagnosis.

Usage hours are the time your machine ran with the mask on in a night. Machines sum all on-mask periods between start and stop.

VAuto is ResMed's auto-adjusting bilevel mode on AirCurve VAuto machines. EPAP rises and falls with your needs and IPAP follows it at a set pressure support above.

A waveform is the continuous trace of airflow, pressure or leak through the night, recorded several times a second. ResMed machines save it in the DATALOG folder.

What changed? is the Apnealytics panel that lists settings changes, such as pressure, EPR or mask, and points where your trend shifted. It sits on the dashboard and in History.