Sleep Apnea Glossary

Welcome to this comprehensive glossary on sleep apnea and related equipment.

Whether you’re newly diagnosed, seeking clarity, or a seasoned patient looking to deepen your understanding, this curated list provides clear and concise definitions to guide you through the intricacies of sleep apnea care.

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Adherence refers to the consistency with which a patient uses their sleep apnea treatment. Regular usage increases the effectiveness of the therapy.


Aerophagia is the swallowing of air, sometimes a side effect of CPAP therapy. This can lead to bloating and discomfort in some individuals.


An apnea is a pause in breathing during sleep, lasting at least 10 seconds. It can be caused by blocked airways or a lapse in the brain’s signaling.

Apnea-Hypopnea Index (AHI)

AHI measures sleep apnea severity by calculating the number of apneas and hypopneas per hour. A higher AHI indicates greater sleep disruption.

Auto-Adjusting Positive Airway Pressure (APAP)

APAP machines automatically adjust the air pressure based on the patient’s needs. This differs from standard CPAP machines which maintain a constant pressure.


Bi-level Positive Airway Pressure (BiPAP or BPAP)

BiPAP machines provide two levels of air pressure: one for inhalation and a lower one for exhalation. They are often prescribed for patients who find a constant pressure uncomfortable.


Central Alveolar Hypoventilation

This is a reduced drive to breathe during sleep, which results in elevated carbon dioxide levels. It’s less common than other forms of sleep apnea.

Central Sleep Apnea (CSA)

CSA occurs when the brain fails to send proper signals to the muscles controlling breathing. This is different from OSA, where the airway is physically blocked.


A chinstrap is worn to prevent the mouth from opening during CPAP therapy. This helps improve the effectiveness of nasal masks.

Complex Sleep Apnea Syndrome (CompSA)

CompSA is a condition combining features of both OSA and CSA. Patients with this syndrome often require specialized treatments.

Compliance Monitoring

Compliance monitoring tools track how often and how long a patient uses their CPAP or BiPAP machine. This helps doctors ensure that patients are getting adequate therapy.

Continuous Positive Airway Pressure (CPAP)

CPAP therapy uses mild air pressure to keep airways open and treat sleep apnea. It’s the most common treatment for OSA.


A CPAP mask delivers air pressure from the machine and is worn over the nose, mouth, or both. A proper mask fit is crucial for effective treatment.



Desaturation indicates a decrease in blood oxygen levels. Severe desaturation can be dangerous and is a concern in untreated sleep apnea.


EPAP (Expiratory Positive Airway Pressure)

In bilevel therapy, EPAP is the pressure applied during exhalation. It’s typically lower than the inhalation pressure.

Exhalation Relief

Exhalation relief features reduce the pressure during exhalation, making breathing more comfortable during CPAP therapy.



Filters are found in CPAP/BiPAP machines to purify the air being delivered to the patient. They need regular replacement for optimal performance.

Full Face Mask

A full face mask covers both the nose and mouth. It’s ideal for patients who breathe through their mouths during sleep.


Heated Tubing

Heated tubing warms the air from CPAP/BiPAP machines, which can increase comfort and prevent condensation within the hose.


Humidifiers add moisture to the air delivered by CPAP/BiPAP machines. This helps reduce symptoms like dry mouth and nasal congestion.


Hypercapnia is the presence of elevated carbon dioxide levels in the blood. It can result from inadequate ventilation or respiratory problems.


Hypopnea is a reduction in airflow during sleep that doesn’t result in complete cessation. It leads to a drop in oxygen levels and disrupts sleep.


Hypoxia refers to low oxygen levels in the blood. It’s a concern in untreated sleep apnea as it can lead to other health complications.


Inspiratory Flow Limitation

This refers to reduced airflow during inhalation despite an increase in effort. It can disrupt sleep and lead to daytime fatigue.

IPAP (Inspiratory Positive Airway Pressure)

IPAP is the pressure applied during inhalation in bilevel therapy. It’s typically higher than the exhalation pressure.


Lateral Position

The lateral position involves lying on one’s side. For some individuals, this position can help reduce sleep apnea events.

Leak Rate

Leak rate measures the amount of air that leaks out of the mask during therapy. A high leak rate can compromise the efficacy of the therapy.


Mandibular Advancement Device (MAD)

MAD is an oral appliance that repositions the lower jaw forward to prevent airway obstruction. It’s an alternative to CPAP therapy for some patients.

Mask Fit

Mask fit refers to how well the CPAP mask seals and remains in place on the user’s face. An improper fit can reduce the effectiveness of the therapy.


Nasal Congestion

Nasal congestion is a blocked or stuffy nose which can affect both sleep and the efficacy of CPAP therapy. Some patients require a full face mask to bypass this issue.

Nasal Mask

A nasal mask covers only the nose and delivers air pressure from the machine. It’s one of the most common types of CPAP masks.

Nasal Pillows

Nasal pillows are small, soft prongs that fit into the nostrils. They are an alternative to traditional CPAP masks and are popular for their minimalistic design.

Night Sweats

Night sweats involve excessive sweating during sleep and can sometimes be linked to sleep apnea. They may also have other underlying causes.


Nocturia involves frequent urination at night and can be associated with sleep apnea. It can disrupt sleep and lead to daytime fatigue.


Obstructive Sleep Apnea (OSA)

OSA is the most common type of sleep apnea, caused when throat muscles relax and obstruct the airway. Snoring, choking, and frequent awakenings are common symptoms.


Oximetry measures the oxygen saturation in the blood. It’s a useful tool in diagnosing and monitoring sleep disorders.

Oxygen Desaturation

This is a drop in the level of oxygen in the blood. It often occurs during episodes of apnea or hypopnea.


Polysomnography (PSG)

PSG is a comprehensive sleep study used to diagnose sleep disorders. It monitors various body functions during sleep.

Positional Therapy

Positional therapy involves changing the patient’s sleep position to improve breathing. For some, avoiding the back position reduces sleep apnea events.

Pressure Sores

Pressure sores can develop from a CPAP mask pressing too tightly against the skin. Proper mask fitting can help prevent this issue.


Ramp Feature

The ramp feature allows a machine to start at a lower pressure, gradually increasing to the prescribed pressure. This eases the user into their therapy each night.

RERA (Respiratory Effort Related Arousal)

RERA is a sequence of breathing disturbances leading to arousal from sleep. It’s a sign of disrupted sleep quality.


Sleep Apnea

Sleep apnea is a disorder characterized by repeated pauses in breathing during sleep. It can lead to daytime fatigue, heart problems, and other health complications.

Sleep Fragmentation

Sleep fragmentation involves frequent awakenings or shifts between sleep stages. It’s a common outcome of untreated sleep apnea and results in poor sleep quality.


Snoring involves loud breathing sounds during sleep and is often associated with OSA. While not all snorers have sleep apnea, it’s a common symptom.


Somnolence is characterized by excessive daytime sleepiness. It’s a common symptom in those with sleep apnea and other sleep disorders.

Supine Position

The supine position involves lying on one’s back. Some individuals experience more sleep apnea events in this position.


Tongue Retaining Device

This oral appliance holds the tongue forward to prevent it from blocking the airway. It’s an alternative to CPAP for some patients.


Titration is the process of adjusting the pressure settings on a CPAP or BiPAP machine to find the optimal level for a patient. It’s often done during a sleep study.


Upper Airway Resistance Syndrome (UARS)

UARS is a sleep disorder with symptoms similar to OSA but results from resistance in the upper airway. It can cause significant daytime fatigue.