CPAP and Sleep Apnea Glossary

A complete pause in breathing lasting at least 10 seconds during sleep. Apneas are classified as obstructive (airway physically blocked), central (brain fails to signal breathing muscles), or mixed (starts as central, becomes obstructive).

Why it matters: Apneas are the core events your CPAP treats. Your AHI counts how many of these happen per hour. Fewer apneas means your therapy is working.

The number of apneas and hypopneas per hour of sleep. It is the primary metric used to diagnose sleep apnea severity and measure treatment effectiveness. Normal is below 5, mild is 5 to 14, moderate is 15 to 29, and severe is 30 or above.

Why it matters: AHI is the single most important number on your CPAP report. Your doctor uses it to gauge whether your therapy is controlling your sleep apnea. Most insurance requires AHI below 5 on treatment.

A CPAP machine that automatically adjusts pressure throughout the night based on detected breathing events. It operates within a set pressure range (e.g., 6 to 14 cmH2O) rather than delivering a single fixed pressure.

Why it matters: Most modern CPAP machines (like the ResMed AirSense 10/11 AutoSet) use auto-titration. It means your machine is constantly adapting to keep your airway open at the lowest effective pressure, improving comfort.

A device that delivers two different pressure levels: a higher pressure when you inhale (IPAP) and a lower pressure when you exhale (EPAP). Used for patients who need higher pressures or have difficulty exhaling against CPAP pressure.

Why it matters: If standard CPAP feels hard to breathe against, bilevel therapy can be more comfortable. AirCurve machines use bilevel mode. Your SD card data will show both IPAP and EPAP values.

A pause in breathing caused by the brain temporarily failing to send signals to the breathing muscles. Unlike obstructive apneas, the airway is not physically blocked.

Why it matters: Central apneas are not caused by airway collapse, so increasing CPAP pressure will not fix them. If your data shows a high proportion of central events, your doctor may need to adjust your approach.

A cyclical breathing pattern where breathing gradually increases in depth, then decreases, followed by a pause. Often associated with heart failure and central sleep apnea.

Why it matters: CPAP Clarity parses CSR episodes from your SD card data. If CSR appears in your reports, it is important to discuss with your doctor as it may indicate an underlying cardiac condition.

Centimeters of water pressure. The unit used to measure CPAP air pressure. Typical CPAP pressures range from 4 to 20 cmH2O.

Why it matters: When you see pressure values in your CPAP data (like 10.2 cmH2O), this is the force keeping your airway open. Higher is not always better. Your machine finds the lowest pressure that controls your events.

Co-Morbid Insomnia and Sleep Apnea. A condition where a patient has both clinically significant insomnia and obstructive sleep apnea simultaneously. Affects 30 to 50% of OSA patients.

Why it matters: If you have COMISA, treating only the apnea with CPAP may not resolve your sleep problems. Both conditions need to be addressed for the best outcomes.

Meeting the minimum CPAP usage requirements set by insurance providers. The most common standard (Medicare) requires using CPAP for at least 4 hours per night on at least 70% of nights during a consecutive 30-day period within the first 90 days.

Why it matters: Failing compliance can mean losing insurance coverage for your CPAP equipment. Track your usage carefully during the initial compliance period.

A treatment for obstructive sleep apnea that delivers a constant stream of pressurized air through a mask to keep the airway open during sleep. The pressure is measured in centimeters of water (cmH2O).

Why it matters: CPAP is the gold-standard treatment for obstructive sleep apnea. Understanding how it works helps you get the most from your therapy.

A drop in blood oxygen levels (SpO2), typically defined as a decrease of 3% or more from baseline. Desaturations occur when apneas or hypopneas interrupt normal breathing.

Why it matters: Frequent desaturations mean your brain and organs are not getting enough oxygen during sleep. Effective CPAP therapy should minimize these events.

Medical equipment prescribed for long-term use, including CPAP machines, masks, tubing, and accessories. DME suppliers handle insurance billing and equipment delivery.

Why it matters: Your DME supplier is who you contact for replacement masks, tubing, and filters. Understanding the DME process helps you stay on top of supply replacements.

European Data Format. A standard file format for storing physiological signal data. ResMed CPAP machines write detailed session data to SD cards in EDF format.

Why it matters: EDF files on your SD card contain the detailed pressure, flow, leak, and event data that CPAP Clarity reads. This is the raw data behind your nightly metrics.

A validated 8-question screening tool that measures daytime sleepiness by rating your likelihood of dozing in common situations. Scores range from 0 to 24, with 10 or above suggesting excessive daytime sleepiness.

Why it matters: The ESS helps you and your doctor assess whether your sleep apnea treatment is reducing daytime sleepiness. A persistently high ESS despite good AHI control may suggest other sleep issues.

A ResMed comfort feature that reduces air pressure during exhalation by 1 to 3 cmH2O, making it easier to breathe out against the CPAP pressure. Other manufacturers call this C-Flex (Philips) or Reslex (BMC).

Why it matters: EPR can dramatically improve comfort, especially at higher pressures. If CPAP feels hard to exhale against, increasing your EPR setting (up to 3) is often the first adjustment to try.

A partial narrowing of the airway that restricts airflow without completely blocking it. It appears as a flattened shape on the flow waveform graph and often precedes obstructive events.

Why it matters: High flow limitation means your airway is partially collapsing even though full apneas may not be occurring. Your APAP machine uses flow limitation to decide when to increase pressure.

A CPAP mask that covers both the nose and mouth. Recommended for mouth breathers or people who cannot maintain a seal with nasal masks.

Why it matters: Choosing the right mask type is one of the biggest factors in CPAP comfort and compliance. Full face masks are the best option if you breathe through your mouth during sleep.

A heated water chamber attached to or built into your CPAP machine that adds moisture to the pressurized air. Most modern CPAP machines include an integrated humidifier.

Why it matters: Dry air from CPAP can cause nasal congestion, dry mouth, nosebleeds, and discomfort. Adjusting humidity settings can solve many common CPAP side effects.

A partial reduction in airflow (at least 30%) lasting at least 10 seconds, accompanied by a drop in oxygen saturation or an arousal from sleep. Less severe than a full apnea but still disruptive.

Why it matters: Hypopneas are counted alongside apneas in your AHI. They are more common than full apneas in many patients and contribute significantly to fragmented sleep and daytime fatigue.

A validated 7-question screening tool that measures insomnia severity on a 0 to 28 scale. Categories range from no clinically significant insomnia (0 to 7) to severe (22 to 28).

Why it matters: 30 to 50% of sleep apnea patients also have insomnia. If your CPAP data looks good but you still cannot sleep, the ISI can help quantify the insomnia component.

Inspiratory Positive Airway Pressure. The higher pressure delivered by a bilevel (BiPAP) machine during inhalation.

Why it matters: On bilevel machines, the gap between IPAP and EPAP (called pressure support) determines how much the machine assists your breathing. Your SD card data shows both values.

The amount of air escaping from your CPAP mask, measured in liters per minute (L/min). Includes intentional leak (designed exhaust vents) and unintentional leak (poor mask seal).

Why it matters: High unintentional leak reduces therapy effectiveness because your machine cannot maintain proper pressure. CPAP Clarity shows your leak data so you can identify which nights had seal problems.

The actual air pressure measured at the mask, as opposed to the pressure the machine is generating. Mask pressure may be slightly lower than machine pressure due to tubing resistance.

Why it matters: Your SD card data contains mask pressure readings. This is the pressure actually reaching your airway, which is what matters for therapy effectiveness.

The total volume of air you breathe per minute, calculated as tidal volume multiplied by respiratory rate. Measured in liters per minute.

Why it matters: Changes in minute ventilation can indicate breathing instability. A sudden drop may precede apnea events. Your SD card data may include MV if your machine records it.

An apnea event that starts as a central apnea (no breathing effort) and transitions into an obstructive apnea (effort against a closed airway). Counted in your AHI alongside other apnea types.

Why it matters: Mixed apneas suggest both central and obstructive components. If you see a significant number, discuss with your doctor as it may affect treatment decisions.

ResMed's companion app for AirSense 10 and 11 machines. Provides a simplified daily score (0 to 100) based on usage hours, mask seal, events per hour, and mask on/off events.

Why it matters: myAir gives you a quick daily check-in but hides the detailed data. CPAP Clarity reads the same SD card data but shows you everything: full event breakdowns, pressure charts, and detailed metrics.

A CPAP mask that covers only the nose. Available in nasal cradle, nasal pillow, and over-the-nose styles. Generally lighter and less claustrophobic than full face masks.

Why it matters: Nasal masks tend to have better seal characteristics and lower leak rates. If you can breathe through your nose during sleep, they are usually the first choice.

A minimal CPAP mask with small cushions that seal at the nostrils. The lightest and least obtrusive mask type. Popular models include the ResMed AirFit P10 and P30i.

Why it matters: If you feel claustrophobic with larger masks or sleep on your side/stomach, nasal pillows offer the smallest footprint and most freedom of movement.

A pause in breathing caused by physical collapse or blockage of the upper airway, despite ongoing effort to breathe. The most common type of sleep apnea event.

Why it matters: Obstructive apneas are what CPAP is designed to treat. The machine's air pressure acts as a pneumatic splint to keep your airway open.

A sleep disorder characterized by repeated episodes of complete or partial upper airway obstruction during sleep. The most common form of sleep apnea, affecting an estimated 26% of adults aged 30 to 70.

Why it matters: OSA is the condition your CPAP treats. Understanding it helps you understand why consistent therapy matters and what your data means.

Open Source CPAP Analysis Reporter. A free, open-source desktop application for analyzing CPAP data. Supports multiple machine brands and provides detailed waveform-level data.

Why it matters: OSCAR is the most powerful CPAP data tool available but has a steep learning curve. CPAP Clarity provides a simpler web-based alternative that reads the same SD card data.

The number of times per hour that blood oxygen levels drop by 3% or more from baseline. Measured during a sleep study using pulse oximetry.

Why it matters: ODI complements AHI by showing how much your oxygen levels actually dip. A high ODI with a low AHI may indicate that your breathing events, while few, are causing significant oxygen drops.

An overnight sleep study conducted in a lab that records brain waves (EEG), eye movements, muscle activity, heart rhythm, breathing, and blood oxygen. The gold standard for diagnosing sleep disorders.

Why it matters: A PSG provides the most comprehensive sleep evaluation. If you were diagnosed via a home sleep test, a lab PSG may be recommended if your results were inconclusive or if central apnea is suspected.

The difference between IPAP and EPAP on a bilevel machine. For example, if IPAP is 14 and EPAP is 10, pressure support is 4 cmH2O.

Why it matters: Pressure support determines how much extra help you get when breathing in. Higher PS assists ventilation more but can cause air swallowing (aerophagia) if set too high.

Condensation that collects in the CPAP tubing when warm, humidified air cools as it travels from the machine to the mask. Can cause water dripping or gurgling sounds.

Why it matters: Rainout is one of the most common CPAP complaints. Using a heated hose, adjusting humidity, or changing the machine's position relative to your bed usually fixes it.

A comfort feature that starts CPAP pressure low and gradually increases to your prescribed level over a set time (typically 5 to 45 minutes), making it easier to fall asleep.

Why it matters: If falling asleep with full pressure feels uncomfortable, ramp lets you drift off at a lower pressure. Your SD card data shows when ramp ends and full therapy begins.

Respiratory Effort-Related Arousal. A breathing event where increasing effort to breathe causes a brief awakening (arousal) from sleep, without meeting the criteria for an apnea or hypopnea.

Why it matters: RERAs fragment your sleep without showing up in your AHI. If you feel tired despite a low AHI, RERAs or upper airway resistance syndrome (UARS) may be a factor.

Similar to AHI but also includes respiratory effort-related arousals (RERAs) in addition to apneas and hypopneas. RDI is always equal to or greater than AHI.

Why it matters: Some sleep labs report RDI instead of AHI. If your RDI is significantly higher than your AHI, it means you have frequent arousals from subtle breathing disruptions even without full apneas.

The number of breaths per minute. Normal adult respiratory rate during sleep is 12 to 20 breaths per minute.

Why it matters: Unusually high or low respiratory rates in your CPAP data can indicate breathing instability. Consistent rates suggest stable, effective therapy.

A removable memory card in your CPAP machine that stores detailed therapy data including pressure, airflow, leak, respiratory events, and machine settings. Standard SD or micro-SD depending on the machine model.

Why it matters: Your SD card contains far more data than what myAir or your machine's screen shows. CPAP Clarity reads this raw data to give you detailed analysis.

The percentage of time spent asleep versus time spent in bed. Calculated as total sleep time divided by total time in bed. Normal sleep efficiency is 85% or higher.

Why it matters: Low sleep efficiency means you are spending a lot of time in bed awake. This can indicate insomnia, poor sleep habits, or discomfort from CPAP.

The time it takes to fall asleep after getting into bed and turning off the lights. Normal sleep latency is 10 to 20 minutes.

Why it matters: Falling asleep in under 5 minutes often indicates significant sleep deprivation rather than good sleep. Taking more than 30 minutes may suggest insomnia. CPAP ramp time should account for your typical sleep latency.

A diagnostic test that monitors your body during sleep to detect sleep disorders. Can be conducted in a sleep lab (polysomnography) or at home (home sleep test).

Why it matters: A sleep study is required to diagnose sleep apnea and determine appropriate treatment pressure. Results include your diagnostic AHI, oxygen levels, and sleep staging.

Peripheral oxygen saturation. The percentage of hemoglobin in the blood that is carrying oxygen, measured non-invasively by a pulse oximeter. Normal levels are 95% to 100%.

Why it matters: Sleep apnea causes SpO2 drops during breathing pauses. Monitoring SpO2 with a pulse oximeter can help you and your doctor assess how effectively your CPAP prevents oxygen desaturation.

A validated 8-question screening tool for obstructive sleep apnea risk. Assesses Snoring, Tiredness, Observed apneas, blood Pressure, BMI, Age, Neck circumference, and Gender.

Why it matters: STOP-BANG is one of the most widely used OSA screening tools. A score of 5 or higher indicates high risk and warrants a sleep study.

CPAP Clarity's composite score from 0 to 100 that combines AHI control (40%), usage hours (30%), mask seal quality (20%), and nightly consistency (10%).

Why it matters: The Therapy Score gives you one number to track over time. It weights the factors your doctor cares about most, making it easy to see if your therapy is trending better or worse.

The volume of air moved in and out of the lungs with each breath, measured in milliliters (mL). Normal adult tidal volume during sleep is approximately 300 to 500 mL.

Why it matters: Low tidal volumes may indicate shallow breathing or mask leak. Your SD card data includes tidal volume readings that can help identify breathing pattern issues.

A sleep study specifically designed to determine the optimal CPAP pressure for a patient. May be a full-night study or a split-night study (diagnostic first half, titration second half).

Why it matters: Your prescribed pressure comes from a titration study. If your auto-CPAP consistently settles at a pressure very different from your prescribed range, a new titration may be warranted.

Central apneas that appear or worsen after starting CPAP therapy, despite resolution of obstructive events. Also called complex sleep apnea. Occurs in 5 to 15% of CPAP patients.

Why it matters: If your CPAP data shows increasing central apneas after treatment starts, do not panic. TECSA often resolves within weeks. If it persists, your doctor may consider ASV therapy.

A sleep disorder where the airway narrows enough to cause arousals and fragmented sleep, but not enough to meet the criteria for apneas or hypopneas. Results in a normal AHI but high RDI.

Why it matters: UARS can cause significant daytime sleepiness and fatigue despite a normal AHI. If your AHI is low but you still feel exhausted, UARS may be worth discussing with your doctor.

The amount of time you use your CPAP per night, measured from when the mask is on and pressure is being delivered. Most machines count time at therapeutic pressure, excluding ramp time.

Why it matters: Insurance compliance requires at least 4 hours per night on 70% of nights. But research shows 6 or more hours provides the most benefit. Your SD card data shows exact usage for every night.

ResMed's variable bilevel mode available on AirCurve machines. Automatically adjusts both IPAP and EPAP within set ranges, combining the benefits of auto-titration with bilevel pressure support.

Why it matters: If you use an AirCurve in VAuto mode, your SD card data will show both IPAP and EPAP values. CPAP Clarity calculates the I:E ratio and inspiratory time from this data.