CPAP and sleep apnea glossary

CPAP and Sleep Apnea Glossary

Medical sleep vocabulary can seem confusing. This glossary explains in plain language the terms you will encounter with your doctor, on your CPAP device, or in your insurance documents.

Aerophagia

Swallowing air under pressure during CPAP therapy, causing bloating, gas, and belching. Often signals pressure that is too high. Solutions: reduce pressure (with medical advice), activate EPR/C-Flex, or try BiPAP.

AHI - Apnea-Hypopnea Index

Measures the number of apneas and hypopneas per hour of sleep. The main indicator of sleep apnea severity. Thresholds: < 5 = normal, 5-15 = mild, 15-30 = moderate, > 30 = severe.

AHIO (Belgian equivalent of AHI)

Index d'Apnées-Hypopnées Obstructives - the preferred term in Belgian INAMI nomenclature. Adult INAMI criteria: AHIO ≥ 15/hour. Children (< 16 years): AHIO ≥ 1/hour.

AirView

ResMed's remote monitoring platform allowing providers and physicians to review CPAP data remotely (residual AHI, leaks, usage hours). Integrated into ResMed devices via SIM card or Wi-Fi.

APAP (Auto-CPAP / AutoPAP)

A CPAP variant that automatically adjusts pressure in real time based on detected respiratory events. More comfortable than fixed-pressure CPAP for most patients. Recommended as first-line therapy. See our Auto CPAP devices.

Arousal (micro-arousal)

A brief awakening of the brain (3 to 15 seconds) at the end of an apnoea, which allows breathing to resume. The patient does not remember it, but it is visible on polysomnography. Dozens of arousals per hour fragment sleep and explain daytime tiredness.

ASV (Adaptive Servo-Ventilation)

A sophisticated ventilator that adapts pressure to each breath cycle to stabilize ventilation. Used for complex central apneas, Cheyne-Stokes breathing, and treatment-emergent central apneas resistant to standard CPAP.

Berlin questionnaire

A sleep apnoea screening questionnaire in 3 categories (snoring, sleepiness, hypertension and BMI). A high-risk score in at least 2 of the 3 categories indicates a significant risk of apnoea. Sensitivity around 86 % in its validation study.

BIM (increased reimbursement status)

A Belgian social status granting increased reimbursement from the health insurance fund. Within the INAMI CPAP convention, BIM status removes the patient co-payment entirely, making the convention free of charge.

BiPAP (Bi-Level PAP)

Also called BiLevel or VPAP. A ventilation device with two pressure levels: a higher inspiratory pressure (IPAP) and a lower expiratory pressure (EPAP). Used for intolerance to CPAP back-pressure, central apneas, or respiratory insufficiency.

Central apnoea

A pause in breathing caused by a failure of the brain's command: the brain does not send the signal to breathe. The airway is open but there is no respiratory effort. Unlike obstructive apnoea, no physical obstruction is involved.

cmH₂O (centimeters of water)

Unit of CPAP pressure measurement. 1 cmH₂O is the pressure exerted by a column of water 1 centimetre high. CPAPs typically deliver between 4 and 20 cmH₂O depending on patient needs.

Compliance (adherence)

Actual use of the CPAP device. The Belgian INAMI requires an average of at least 4 hours per night, calculated over the reference period, to keep the convention. It is an average, not an absolute minimum every single night.

CPAP (Continuous Positive Airway Pressure)

The gold-standard treatment for moderate to severe obstructive sleep apnea. A device delivers continuously pressurized air through a mask to keep the airways open during sleep.

CPAP Convention (INAMI/RIZIV Belgium)

The Belgian INAMI convention is not a purchase reimbursement: it provides CPAP equipment through an approved sleep center - the patient never owns the device. Patient cost: €0.25/day. Criteria: AHIO ≥ 15/h, compliance ≥ 4h/night average. More details: CPAP reimbursement in Belgium.

EPAP (Expiratory Positive Airway Pressure)

Pressure applied during expiration in a BiPAP system. Lower than IPAP, it keeps the airways open on exhalation without creating excessive resistance. On a standard CPAP, EPAP equals IPAP: a single constant pressure.

EPR (Expiratory Pressure Relief)

ResMed technology that automatically reduces CPAP pressure during expiration (equivalent to C-Flex by Philips). Improves comfort. Available in 3 levels.

ESS (Epworth Sleepiness Scale)

An 8-question survey measuring daytime sleepiness across daily situations. Score 0-24. Score ≥ 11: excessive daytime sleepiness requiring medical evaluation.

Full face mask

A CPAP mask covering the nose AND the mouth. Recommended for mouth breathers or patients with heavy nasal congestion. Fewer mouth leaks. Examples: AirFit F20, AirFit F40.

Heated humidifier

A module built into the CPAP device, or external, that humidifies and warms the delivered air. It reduces nasal dryness, congestion and nosebleeds. Use distilled water only. Strongly recommended for long-term tolerance.

Hypopnea

Partial reduction of airflow (≥ 30%) lasting at least 10 seconds, associated with an oxygen desaturation or arousal. Less severe than a complete apnea but included in the AHI calculation.

INAMI / RIZIV

Institut National d'Assurance Maladie-Invalidité (in Dutch: Rijksinstituut voor Ziekte- en Invaliditeitsverzekering). The Belgian body that runs health social security. It frames the CPAP convention, sets the coverage conditions and oversees the accredited centres.

IPAP (Inspiratory Positive Airway Pressure)

Pressure applied during inspiration in a BiPAP system. Higher than EPAP, it helps keep airways open and facilitates air entry into the lungs.

Leak

Air escaping between the mask and the face, or through the mouth with a nasal mask. It lowers the pressure that actually reaches the airway and distorts the residual AHI reading. It is the first cause of an ineffective treatment.

Mixed apnoea

An apnoea that starts as a central apnoea (no respiratory effort) and then becomes obstructive (airway collapse). It can appear under CPAP therapy in some patients, which is referred to as complex apnoea.

Nasal mask

A CPAP mask covering the nose only, from the bridge of the nose to the upper lip. A compromise between the full face mask and nasal pillows. The most common type. Example: AirFit N20.

Nasal pillows mask

A minimalist CPAP mask made of small cushions that sit at the nostrils. Minimal contact with the face, ideal for claustrophobic users and for beard wearers. Example: AirFit P10.

OAM (Mandibular Advancement Device / MAD)

A custom dental device worn at night that advances the lower jaw to widen the upper airways. Second-line treatment for mild to moderate apnea, or as a CPAP alternative. Prescribed by a dentist specialized in sleep medicine.

Obstructive apnoea

A pause in breathing of at least 10 seconds caused by the collapse of the upper airway, despite continued respiratory effort. It accounts for about 90 % of sleep apnoeas and responds well to CPAP.

OSA (Obstructive Sleep Apnea)

Cessation of breathing for ≥ 10 seconds caused by collapse of the upper airways despite continued respiratory effort. Accounts for ~90% of sleep apnea cases. Effectively treated by CPAP.

OSCAR

Free open-source software for detailed analysis of CPAP data (residual AHI, leaks, pressure histogram, breathing waveform). Compatible with major manufacturers. Widely used by patients wanting to optimize their therapy.

Oxygen desaturation

A drop in blood oxygen level (SpO2) during an apnoea or a hypopnoea. A desaturation of 3 % or more associated with a respiratory event is diagnostically significant.

Patient co-payment (CPAP convention)

The share of the cost left to the patient under the Belgian CPAP convention: 0.25 € per day, or 7.50 € per month. It is waived for BIM beneficiaries.

Polygraphy (ambulatory)

At-home sleep apnea screening test measuring airflow, thoracic movements, SpO2 and heart rate. Sufficient for diagnosis in most cases. Reimbursed by Belgian health insurance.

Polysomnography (PSG)

The gold-standard sleep study conducted in a sleep center. Records EEG (brain activity), EMG (muscles), EOG (eye movements), airflow, respiratory movements, SpO2, and posture. Reimbursed by Belgian health insurance.

Rainout

Condensation forming in the CPAP tube when humidified air cools in transit. Causes gurgling and water droplets in the mask. Solution: heated tubing (ClimateLine, etc.) or tube insulation.

Ramp function

CPAP function that starts at a low pressure (often 4 cmH₂O) and gradually rises to therapeutic pressure during sleep onset (15-30 minutes). Greatly facilitates adaptation.

SpO2 (oxygen saturation)

Non-invasive measurement of blood oxygen saturation via a finger pulse oximeter. Normal value: 95-100%. Repeated drops during sleep indicate significant nocturnal hypoxia.

STOP-BANG

8-question Yes/No sleep apnea screening questionnaire (Snoring, Tired, Observed, Pressure, BMI, Age, Neck, Gender). Score ≥ 3: intermediate risk. Score ≥ 5: high risk. Widely used in pre-operative assessment and in general practice.

Titration

An in-center sleep study to determine optimal CPAP pressure. The patient sleeps with CPAP while a technician adjusts pressure in real time to eliminate all apneas. Required for the INAMI convention.

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