Sleep apnea glossary

How much you actually use your CPAP, as recorded by the machine. The convention requires at least 4 hours a night on average: it is an average, not a minimum for every single night. Usage is checked over at least 2 months for the first renewal, then over at least 9 months.

Air swallowed during CPAP that ends up in your stomach, causing bloating, gas and burping when you wake up. It often means the pressure isn't set right, so talk to your doctor rather than changing the settings yourself.

The number of apneas and hypopneas per hour of sleep, and the main measure of how severe sleep apnea is: 15 to 29 an hour counts as moderate, 30 or more as severe. The Belgian CPAP convention uses a narrower figure, the OAHI, which counts obstructive events only.

A CPAP that adjusts its own pressure through the night, within a minimum and maximum set by your doctor. In Belgium, the convention also allows it to be used at home for titration in some patients.

A brief shift in brain activity toward wakefulness, lasting at least 3 seconds and visible on the EEG. It often comes at the end of an apnea or hypopnea, and the person doesn't remember it. When arousals keep happening, they break up sleep and can leave you tired the next day.

A machine that adjusts its support breath by breath to even out unstable breathing. It is used for some forms of central apnea, Cheyne-Stokes breathing, and central apneas that persist on CPAP. In people with heart failure, an ejection fraction of 45% or less and mainly central apneas, the SERVE-HF trial found higher mortality with ASV, so cardiologists and sleep doctors take this into account.

A heart rhythm disorder in which the upper chambers of the heart beat fast and irregularly. Obstructive sleep apnea is linked to a higher risk of AFib. After catheter ablation, patients with sleep apnea who use CPAP have fewer recurrences in observational studies, but the only randomized trial found no difference.

A sleep apnea screening questionnaire with three categories: snoring, daytime tiredness and sleepiness, and high blood pressure or a BMI over 30. Two or more positive categories point to a high risk. Like any questionnaire, it can flag a risk, but it can't diagnose sleep apnea.

A Belgian status that entitles you to higher reimbursement of health care costs. Under the CPAP convention, patients with BIM status don't pay the €0.25 daily co-payment, so their treatment costs them nothing.

A machine with two pressure levels: higher when you breathe in (IPAP) and lower when you breathe out (EPAP). Doctors may suggest it in particular situations, for example when a high pressure is hard to tolerate.

Weight relative to height: your weight in kilograms divided by your height in meters squared. The WHO defines obesity as a BMI of 30 or more. Excess weight is one of the main risk factors for obstructive sleep apnea. BMI is part of the STOP-BANG questionnaire (over 35) and of the Hoffstein formula.

A Philips feature that lowers the pressure slightly as you start to breathe out. It makes exhaling more comfortable if you feel like you're blowing against the machine.

The recommended first-line treatment for chronic insomnia, ahead of sleeping pills, notably by the 2023 European guideline. It works on the habits and thoughts that keep insomnia going. It can also help people with sleep apnea who struggle with insomnia as well.

A pause in breathing during sleep with no effort to breathe at all: for a moment, the brain stops sending the signal to the breathing muscles. That is what sets it apart from obstructive apnea, where the chest keeps working against a closed throat.

A strap worn around the head and under the chin to keep your mouth closed on CPAP, with a nasal or nasal pillows mask. It cuts down on mouth leaks and on waking up with a dry mouth. The alternative is a full face mask.

Central apneas that appear when someone being treated for obstructive sleep apnea starts CPAP. They affect a minority of patients (3.5% to 20%, depending on the study) and usually clear up within a few weeks to a few months. If they don't, your doctor may suggest adaptive servo-ventilation (ASV).

The number NIHDI gives the CPAP convention in its official documents. It is the same convention, not another scheme: its daily rates are listed under this number in NIHDI circulars.

One of the main treatments for obstructive sleep apnea. A machine blows air at gentle pressure through a mask to keep your throat open while you sleep. In Belgium, the machine is provided by a sleep center under the NIHDI convention.

The convention between NIHDI and the sleep centers that have signed it, covering the diagnosis and treatment of sleep apnea with CPAP or an oral appliance. The center provides the machine, your health insurance fund pays the center directly, and you pay €0.25 a day (€7 to €8 a month). The main conditions: an OAHI of at least 15 per hour on polysomnography (from age 16), then using the machine at least 4 hours a night on average. The first approval lasts 3 months, and each one after that lasts 12 months.

The pressure of the air your CPAP delivers, measured in centimeters of water (cmH₂O). It is set during titration. An APAP varies it automatically between two prescribed limits, for example 6 and 14 cmH₂O.

A company the sleep center can hand part of the treatment over to: delivering and setting up the machine, masks, technical follow-up. It works under contract with the center, which remains responsible for your treatment. It is often the one you call about a mask or machine problem.

The 2014 EU directive on driver's licenses that brought obstructive sleep apnea into the medical standards for driving. In Belgium, those standards are set out in Annex 6 of the Royal Decree of March 23, 1998: moderate or severe sleep apnea with daytime sleepiness makes you unfit to drive until effective treatment is in place. Driving anyway is punishable by 8 days to 2 years in prison and a fine of €200 to €2,000, or either one.

A recording of the brain's electrical activity through electrodes placed on the scalp. It is what tells wakefulness apart from the stages of sleep (N1, N2, N3 and REM) and picks up arousals. It is part of polysomnography, but not of respiratory polygraphy.

A ResMed feature that lowers the pressure as you breathe out, so exhaling feels easier. Your CPAP provider turns it on and sets it.

A questionnaire covering 8 everyday situations, each scored from 0 to 3 for your chance of dozing. Totals range from 0 to 24, and a score above 10 indicates excessive daytime sleepiness (Johns and Hocking, 1997).

An abnormal tendency to fall asleep during the day, especially when things are quiet: in a meeting, while reading, as a passenger in a car. It is the most common symptom of sleep apnea, and yet only 15% to 50% of people with sleep apnea report it. The Epworth Sleepiness Scale measures it.

A mask that covers both the nose and the mouth. It suits people who breathe through their mouth or often have a blocked nose, at the cost of a bulkier mask.

The two categories of drivers. Group 1 covers private driving (licenses AM, A, B, B+E, G and so on). Group 2 covers trucks, buses and professional driving such as taxis, ambulances and school transport. For Group 2, fitness to drive is assessed by an accredited medical center, under stricter standards.

A blood test that reflects your average blood sugar over roughly the past three months. In people with type 2 diabetes and sleep apnea, CPAP lowers it by 0.24 points on average (Herth meta-analysis, 11 trials), and more so the longer it is used each night.

A heated water tank, built into the CPAP or added on, that moistens and warms the air. It helps with a dry nose and mouth, congestion and nosebleeds.

CPAP tubing with a built-in heating wire that keeps humidified air warm and prevents condensation (rainout). Most useful in a cool bedroom.

Too much CO₂ in the blood. With a CPAP mask, it can happen if the intentional leak vents are blocked. It causes headaches, confusion and drowsiness, and it can be dangerous.

Breathing that becomes too shallow without stopping completely: airflow drops by at least 30% for at least 10 seconds, along with an oxygen drop of at least 3% or an arousal. These are the AASM rules (2012), which the Belgian convention also uses. Hypopneas count toward the AHI.

Small holes built into the mask that let the air you breathe out, and the CO₂ it carries, escape all the time. Never block them. This is not the same as unintentional leak, which comes from a poorly fitted mask.

The soft part of the mask, usually silicone, that touches your face or nostrils. It has no set lifespan: ResMed advises replacing it when it cracks or tears, or when it no longer seals even though it's properly fitted. A worn cushion leaks.

A hormone your body makes at night to signal that it's time to sleep. In the evening, light, and especially the blue light from screens, slows its production.

An apnea that starts with no effort to breathe, like a central apnea, then turns obstructive: the effort to breathe comes back, but air still can't get through.

A mask that covers only the nose, from the bridge down to just above the upper lip. It sits between the full face mask and the nasal pillows mask.

A minimal mask with two small soft tips that sit at the entrance of your nostrils. It touches your face as little as possible, which helps people who feel closed in by a mask. It is less suitable if you breathe through your mouth.

The measurement around your neck, in centimeters. A thick neck is a risk factor for sleep apnea: STOP-BANG gives a point for a neck over 40 cm. It also goes into the Hoffstein formula, which estimates a starting CPAP pressure.

The Belgian public body that runs the national health insurance system. For sleep apnea, it is NIHDI that signs the convention with sleep centers and sets its conditions and rates.

Getting up at night to urinate. Sleep apnea can be the cause: in men over 60 with sleep apnea, one study found higher nighttime levels of natriuretic peptide, a hormone that makes the body shed water and salt, and lower levels of antidiuretic hormone.

The number of obstructive apneas and hypopneas per hour, measured by polysomnography. Unlike the AHI, it leaves out central events. It is the legal criterion of the Belgian CPAP convention: at least 15 per hour from age 16; under 16, at least 5 per hour, or an obstructive apnea index (OAI) of at least 1.

Airflow stops for at least 10 seconds (it drops by 90% or more) because the throat closes during sleep, even though the chest and belly keep trying to breathe.

A custom-made dental splint, worn at night, that brings the lower jaw forward to keep the airway open. In Belgium, the convention covers it from age 18 for obstructive sleep apnea with an OAHI of at least 15 per hour, once an ENT specialist and a dental specialist (a dentist, orthodontist or maxillofacial surgeon) have confirmed it is suitable. The device belongs to the patient.

The throat closes again and again during sleep, often with symptoms such as daytime sleepiness, although many people with sleep apnea have none at all. It is called moderate at 15 to 29 events per hour, and severe at 30 or more.

A drop in blood oxygen, often at the end of an apnea or hypopnea, measured on your finger with a pulse oximeter (SpO2). A drop of at least 3% is one of the criteria for scoring a hypopnea, under both the AASM rules and the Belgian convention.

The share of the cost you pay yourself once your health insurance fund has paid its part. Under the CPAP convention, it is €0.25 a day, or €7 to €8 a month. Patients with BIM status don't pay it.

The reference sleep test, done overnight in a sleep laboratory. It records brain activity (EEG), eye movements (EOG), muscle activity (EMG), breathing, oxygen, heart rhythm and body position. In Belgium, it is the test the convention requires for the diagnosis.

A painless way to measure the oxygen in your blood with a clip on your fingertip. In a healthy person, saturation is usually between 95% and 100%.

Water droplets that form in the tubing when humidified air cools on its way to the mask. They gurgle and can splash into the mask. The fix: heated tubing, or a tube shielded from the cold air of the bedroom.

A feature that starts at a low pressure and raises it gradually to your prescribed pressure while you fall asleep. On the ResMed AirSense 11, it can be set from 5 to 45 minutes, or to Auto.

Blood pressure that stays too high despite three medications at the highest tolerated dose, one of them a diuretic, confirmed by readings taken outside the doctor's office. Sleep apnea is found in 60% to 90% of these patients.

A simplified recording of breathing: airflow, chest and belly movement, oxygen and heart rate, but no EEG. It can be done at home. Under the Belgian CPAP convention, however, the diagnosis must be made by polysomnography; polygraphy is used to check a pressure that was set at home.

The sound of the soft tissues of the throat vibrating as the airway narrows during sleep. It can happen on its own or be a sign of obstructive sleep apnea.

The percentage of hemoglobin carrying oxygen, measured with a pulse oximeter. Normal is 95% to 100%. It falls during apneas and hypopneas.

An 8-question yes-or-no screening tool: snoring, tiredness, observed apneas, blood pressure, BMI over 35, age over 50, neck circumference over 40 cm, and male sex. A score of 0 to 2 means low risk, 3 or 4 intermediate, and 5 to 8 high. It was developed in Toronto (Chung, 2008) to screen patients before surgery.

Finding the CPAP pressure that gets rid of your apneas. Your doctor decides how: either a polysomnography night at the center, where the pressure is adjusted in real time, or, for some patients (an OAHI of 30 or more, without certain other conditions), a period at home on an auto-CPAP followed by a check recording. The convention requires it before treatment starts.

Air escaping where it shouldn't: around a poorly fitted mask, through a worn cushion or out of an open mouth. It lowers the pressure you actually receive and can wake you up. On ResMed reports, the alert threshold is 24 L/min at the 95th percentile.

The path air takes between the nose and the windpipe: the nose and nasal passages, the pharynx (throat) and the larynx. In obstructive sleep apnea, it is mainly the pharynx that closes during sleep.