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The Ultimate List of Definitions for CPAP Terms

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A sleep apnea diagnosis can bring relief; seemingly unrelated symptoms that range from a sore throat to brain fog and headaches can be traced back to sleep apnea and treated effectively with CPAP therapy. However, you may also find yourself overwhelmed by all the new vocabulary and terminology associated with sleep apnea and its treatment. This guide to CPAP terminology can help you better understand your condition and the therapies that can help.

Sleep Apnea Terms and Definitions

Confused about your doctor’s orders or the results from your sleep study? We’ve arranged sleep apnea and CPAP terms in alphabetical order below with their definitions for easy reference:

AHI (Apnea Hypopnea Index) – Your AHI is a measurement of how many blockages (hypopneas) and times you stop breathing each hour while sleeping. This measurement is typically taken during a sleep study, however, many CPAP machines provide this number to help show how effective your therapy was during the previous night. There are specific thresholds set for a diagnosis of sleep apnea.

APAP/Auto CPAP – APAP stands for “automatic positive airway pressure.” This type of therapy differs from standard CPAP by automatically changing airway pressure throughout the night. The machine automatically adjusts to breathing patterns to deliver the lowest pressure needed at any given time.

BiPAP/BiLevel/VPAPBiLevel therapy, also called variable level therapy, delivers two different levels of air pressure. A higher level is used when you breathe in and a lower level when you breathe out. Some people find that this sort of therapy is more comfortable during sleep.

Central Sleep ApneaCentral Sleep Apnea (CSA) is a type of sleep apnea where breathing stops but airways are not blocked. This type of sleep apnea is caused by an interruption in communication that stops your brain from sending automatic signals to the body to breathe.

CPAP – CPAP stands for “continuous positive airway pressure“. It’s the term for the technology behind your sleep apnea treatment and also refers to the machine itself.

CPAP MaskCPAP masks are used with a CPAP machine to deliver continuous air pressure. There are a range of mask types that include nasal pillows, nasal masks, and full face CPAP masks. You may need to try a few different kinds before settling on the type that is most comfortable for you.

CPAP PressureCPAP pressure refers to the continuous pressure that is asserted by your CPAP machine. Pressure is measured in centimeters of water, which is typically expressed as cmH2O. CPAP pressure should only be adjusted by a medical professional.

Exhalation Reliefexhalation relief is the lowering of pressure during exhalation while using a CPAP machine. All bilevel machines and many standard CPAP machines offer this feature.

Flow Limitation – this refers to events that restrict the flow of air into your upper airway. Typically, this is due to a blockage or obstruction in the airway.

Hypopnea – hypopnea is a partial blockage of your airway that causes shallow breathing. To be considered hypopnea, breathing must be reduced by 50% for 10 seconds or more. Hypopnea is one of the things that health care providers will look for during a sleep study to diagnose sleep apnea.

Mixed Apnea – this type of sleep apnea is characterized by a combination of Obstructive Sleep Apnea and Central Sleep Apnea.

Non-REM Sleep – this sleep cycle is characterized by a lack of eye movement. It is, along with REM sleep, necessary for full and restful sleep.

OSA (Obstructive Sleep Apnea)OSA is one of the three major types of sleep apnea. In this type of sleep apnea, the airway is partially or totally blocked, which interrupts breathing patterns.

Oximeter – an oximeter is a sensor that measures your pulse rate and the amount of oxygen in your blood. It is usually used during a home sleep test.

Periodic Breathing – periodic breathing is an unstable breathing pattern that happens during sleep. You will experience periods of deep breaths that are interspersed with times that breathing is shallow or absent. Periodic breathing is a sign of central sleep apnea.

Polysomnography – polysomnography (PSG) is a test that is used to monitor the quality of your sleep. Your brain activity, eye movements, heart rhythm, and other factors will be measured during the test. The test can help diagnose a sleep disorder.

Pressure Port – this is the part of some CPAP masks where pressure lines or oxygen tubes can connect. It allows pressure to be monitored.

ProventProvent Sleep Therapy is an alternative to CPAP therapy for the treatment of OSA. Provent uses microvalves that are placed over each nostril to create airway pressure each time you exhale. This prevents the airway collapse that is found in Obstructive Sleep Apnea. The devices are disposable and a new one is used each day.

Rainoutrainout is the condensation or water droplets that form in your CPAP mask or tubing. Rainout becomes more likely when your bedroom is too cold at night while you sleep. Rainout can cause issues with CPAP therapy but can be addressed with some simple solutions like a hose cover or heated tube.

Rampramp or ramping is a process that gradually increases the pressure in your CPAP device by small degrees each night. It is used at the beginning of CPAP therapy to allow you to fall asleep before prescribed pressure is reached.

REM Sleep – rapid eye movement (REM) sleep is one of two recurring sleep cycles you experience each night. This stage of sleep is characterized by rapid movements of the eyelids. It is important to get adequate REM sleep.

Respiratory Rate – this is the number of breaths that you take each minute. This is commonly measured during sleep studies.

ResMed ResMed is a manufacturer of CPAP masks and accessories.

Respironics Phillips Respironics is a manufacturer of CPAP machines, CPAP masks, and other accessories.

Sleep ApneaSleep apnea is a condition which causes an individual to stop breathing during sleep. Sleep apnea can have a number of causes. Proper diagnosis and treatment are necessary to ensure healthy oxygen levels and adequate sleep.

Sleep Apnea Test – A sleep apnea test is a type of sleep study where health professionals assess you for symptoms of sleep apnea. Diagnostic equipment measures to record variables that include breathing-related measurements, blood oxygen levels, and other factors.

Sleep-Disordered  Breathing – Sleep-disordered breathing (SDB) is a blanket term that is used to describe conditions that keep a person from breathing properly while they sleep. The term is interchangeable with “sleep apnea.”

Sleep Stages – During sleep, you go through distinct and important stages throughout the night. Each stage has a purpose. You must enter each to have truly adequate and restorative sleep.

Snore Index – Tour snore index is one of the factors measured during a sleep study. It is the strength of the waves of pressure your snoring makes while you are asleep.

Travel CPAP MachineTravel CPAP machines work the same way that home CPAP machines do. They use a lightweight and compact design to make it easier to take them along during travel. The damage from sleep apnea can be cumulative. If your doctor recommends CPAP therapy, it should be used nightly, even when traveling.

Have a question about a term above or need a word defined that is not on the list? Get in touch! You can also sign up for our newsletter for more useful CPAP and sleep apnea information, as well as valuable savings on CPAP equipment.



  • David Repasky

    David Repasky has been using CPAP treatment since 2017 and has first-hand experience with what it's like to live with Sleep Apnea. He brings the patient's perspective to the CPAP.com blog and has received formal training in CPAP machines, masks, and equipment.

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2 Responses

  1. I can’t seem to get an answer all I want to know is my dream mapper has me at 0% periodic breathing is that bad or is it good what should the percentage be

    1. Hi Ruby, my apologies for the delayed response. The lower the percentage of periodic breathing, the better it is for you, so 0, is great!

      I’m not sure what percentage of periodic is acceptable over 0, so I encourage you to speak with your doctor, or sleep therapist for guidance.

      For other questions, or concerns, please feel free to reach us at: 1-800-356-5221.

      Have a great day!

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