Sleep & CPAP glossary
Plain-language definitions for the sleep study test, sleep apnea test, and CPAP machine rental terms you'll come across while booking a test or arranging therapy.
All glossary terms
AHI (Apnea-Hypopnea Index)
The average number of apneas and hypopneas you experience per hour of sleep. It's the core number used to grade sleep apnea severity: normal is under 5, mild is 5–14, moderate is 15–29, and severe is 30 or more.
Actigraphy
A wrist-worn motion sensor that estimates sleep and wake patterns over several days or weeks. It's a screening tool, not a substitute for a full sleep study test.
Apnea
A pause in breathing during sleep lasting at least 10 seconds — the core event a sleep apnea test is designed to detect and count.
Arousal
A brief shift toward lighter sleep, often triggered by a breathing event, that fragments your night without a full awakening you'd remember.
BiPAP (Bilevel Positive Airway Pressure)
A therapy device that delivers two pressure levels — higher on inhale, lower on exhale — often prescribed when standard CPAP isn't comfortable or effective enough on its own.
BiLevel Titration
The overnight process of finding a patient's ideal BiPAP inhale and exhale pressure settings, usually during a dedicated titration sleep study.
CPAP (Continuous Positive Airway Pressure)
A machine that delivers steady air pressure through a mask to keep your airway open overnight — the first-line therapy for obstructive sleep apnea.
CPAP Machine Rental
Renting a CPAP device on a flexible monthly plan instead of buying one outright, so you can start therapy quickly without a large upfront cost.
CPAP on Rent
Another way of describing CPAP machine rental — accessing a CPAP device month-to-month, with delivery, setup, and ongoing support included.
CPAP Rent
Shorthand for CPAP machine rental: paying a recurring fee to use a CPAP device rather than purchasing one outright.
CPAP Titration Study
An overnight, sensor-monitored study used to work out the exact CPAP pressure that eliminates a diagnosed patient's breathing events.
Central Sleep Apnea
A form of sleep apnea where the brain temporarily stops signaling the breathing muscles, distinct from the airway blockage seen in obstructive sleep apnea.
Cataplexy
Sudden, brief muscle weakness triggered by strong emotion — a hallmark symptom looked for during a narcolepsy sleep study.
Desaturation
A drop in blood oxygen saturation (SpO2), usually caused by a breathing pause, and one of the key signals scored in every sleep study.
Daytime Sleepiness
Persistent drowsiness during waking hours despite a full night in bed — one of the most common reasons people book a sleep apnea test.
EEG (Electroencephalogram)
Sensors that record brain-wave activity during a polysomnography study, used to identify sleep stages and arousals.
Epworth Sleepiness Scale
A short self-reported questionnaire that scores how likely you are to doze off in everyday situations, often used to help decide whether a sleep study test is worth pursuing.
Full Face Mask
A CPAP or BiPAP mask that covers both the nose and mouth, typically recommended for people who breathe through their mouth during sleep.
Home Sleep Test (HSAT)
An overnight, physician-reviewed sleep apnea test performed in your own bed using a small take-home sensor kit, instead of an overnight stay in a lab.
Hypopnea
A partial reduction in airflow during sleep — less severe than a full apnea, but still significant enough to lower oxygen levels or trigger an arousal.
Humidifier
A heated water chamber attached to a CPAP or BiPAP machine that adds moisture to the airflow, reducing dryness and irritation.
In-Lab Sleep Study
A polysomnography test performed overnight at a sleep clinic under technician supervision, typically reserved for complex or ambiguous cases.
Insomnia
Persistent difficulty falling or staying asleep, which may be investigated alongside — or instead of — a sleep apnea test depending on your symptoms.
Level 3 Home Sleep Test
The clinical classification for a simplified home sleep apnea test that records airflow, effort, oxygen, and heart rate, but not brain waves.
MSLT (Multiple Sleep Latency Test)
A series of scheduled daytime nap opportunities, performed the day after an overnight sleep study, used to help diagnose narcolepsy.
Mask Fit
How well a CPAP or BiPAP mask seals against your face — a poor fit is the most common reason people struggle with therapy.
Narcolepsy
A neurological sleep disorder causing excessive daytime sleepiness and sudden sleep episodes, diagnosed through an overnight sleep study followed by an MSLT.
Nasal Cannula
A small tube with two prongs that rests at the nostrils to measure airflow — one of the core sensors used in a home sleep test.
Obstructive Sleep Apnea (OSA)
The most common form of sleep apnea, caused by throat muscles relaxing and repeatedly blocking the airway during sleep.
Oximetry (Pulse Oximeter)
A fingertip sensor that continuously measures blood oxygen saturation (SpO2) and pulse rate throughout a sleep study.
Polysomnography (PSG)
The comprehensive, multi-sensor recording of breathing, oxygen, heart rate, brain waves, and movement during sleep — the clinical gold-standard sleep study.
Parasomnia
Unusual behaviors during sleep, such as sleepwalking or acting out dreams, typically evaluated with a video-assisted sleep study.
PAP Therapy
The umbrella term for positive airway pressure treatments, including CPAP and BiPAP, prescribed after a sleep apnea diagnosis.
Physician-Reviewed Report
The clinical summary a qualified sleep physician prepares after scoring your sleep study, explaining your results and recommended next steps.
REM Sleep
The sleep stage associated with vivid dreaming and rapid eye movement. Breathing muscles relax further in REM, so apnea events are often more frequent.
RERA (Respiratory Effort-Related Arousal)
A breathing event that doesn't fully qualify as an apnea or hypopnea but still triggers a brief arousal from sleep.
Sleep Apnea
A disorder marked by repeated pauses or shallow breaths during sleep — the condition a sleep apnea test is designed to detect and grade.
Sleep Apnea Test
An overnight, sensor-based test — done at home or in a lab — that measures breathing, airflow, and oxygen levels to screen for sleep apnea.
Sleep Apnea Treatment
The therapy path recommended after a diagnosis, ranging from CPAP or BiPAP machine rental to oral appliances or lifestyle changes, based on severity.
Sleep Scan
A common everyday term for an overnight sleep study or sleep apnea test that records your breathing, oxygen, and other signals while you sleep.
Sleep Study
The general term for any overnight, sensor-based recording of sleep — from a basic home sleep test to full in-lab polysomnography.
Sleep Study Test
Another way of referring to a sleep study — the overnight, physician-reviewed test used to diagnose sleep apnea and other sleep disorders.
Somnia Scan
An alternate name sometimes used for a sleep study or sleep scan, referring to the overnight recording of breathing and sleep signals.
SpO2
The medical shorthand for blood oxygen saturation — one of the primary readings tracked throughout a sleep study.
Split-Night Study
A single overnight study that combines sleep apnea diagnosis in the first half of the night with CPAP titration in the second half.
Snoring
The sound caused by vibrating tissue in a narrowed airway. Frequent, loud snoring is one of the most common reasons people request a sleep apnea test.
Titration Study
An overnight study, using CPAP or BiPAP, dedicated to finding the exact pressure setting that keeps a diagnosed patient's airway open.
Turnaround Time
The time between returning your home sleep test device and receiving your physician-reviewed report — typically a few days.
UARS (Upper Airway Resistance Syndrome)
A milder form of airway narrowing that causes arousals and daytime sleepiness without meeting the full criteria for sleep apnea.
Video Polysomnography (Video PSG)
A sleep study that adds synchronized infrared video to standard sensors, used to evaluate parasomnias like sleepwalking or REM behavior disorder.
Glossary terms starting with A
AHI (Apnea-Hypopnea Index)
The average number of apneas and hypopneas you experience per hour of sleep. It's the core number used to grade sleep apnea severity: normal is under 5, mild is 5–14, moderate is 15–29, and severe is 30 or more.
Actigraphy
A wrist-worn motion sensor that estimates sleep and wake patterns over several days or weeks. It's a screening tool, not a substitute for a full sleep study test.
Apnea
A pause in breathing during sleep lasting at least 10 seconds — the core event a sleep apnea test is designed to detect and count.
Arousal
A brief shift toward lighter sleep, often triggered by a breathing event, that fragments your night without a full awakening you'd remember.
Glossary terms starting with B
BiPAP (Bilevel Positive Airway Pressure)
A therapy device that delivers two pressure levels — higher on inhale, lower on exhale — often prescribed when standard CPAP isn't comfortable or effective enough on its own.
BiLevel Titration
The overnight process of finding a patient's ideal BiPAP inhale and exhale pressure settings, usually during a dedicated titration sleep study.
Glossary terms starting with C
CPAP (Continuous Positive Airway Pressure)
A machine that delivers steady air pressure through a mask to keep your airway open overnight — the first-line therapy for obstructive sleep apnea.
CPAP Machine Rental
Renting a CPAP device on a flexible monthly plan instead of buying one outright, so you can start therapy quickly without a large upfront cost.
CPAP on Rent
Another way of describing CPAP machine rental — accessing a CPAP device month-to-month, with delivery, setup, and ongoing support included.
CPAP Rent
Shorthand for CPAP machine rental: paying a recurring fee to use a CPAP device rather than purchasing one outright.
CPAP Titration Study
An overnight, sensor-monitored study used to work out the exact CPAP pressure that eliminates a diagnosed patient's breathing events.
Central Sleep Apnea
A form of sleep apnea where the brain temporarily stops signaling the breathing muscles, distinct from the airway blockage seen in obstructive sleep apnea.
Cataplexy
Sudden, brief muscle weakness triggered by strong emotion — a hallmark symptom looked for during a narcolepsy sleep study.
Glossary terms starting with D
Desaturation
A drop in blood oxygen saturation (SpO2), usually caused by a breathing pause, and one of the key signals scored in every sleep study.
Daytime Sleepiness
Persistent drowsiness during waking hours despite a full night in bed — one of the most common reasons people book a sleep apnea test.
Glossary terms starting with E
EEG (Electroencephalogram)
Sensors that record brain-wave activity during a polysomnography study, used to identify sleep stages and arousals.
Epworth Sleepiness Scale
A short self-reported questionnaire that scores how likely you are to doze off in everyday situations, often used to help decide whether a sleep study test is worth pursuing.
Glossary terms starting with F
Full Face Mask
A CPAP or BiPAP mask that covers both the nose and mouth, typically recommended for people who breathe through their mouth during sleep.
Glossary terms starting with H
Home Sleep Test (HSAT)
An overnight, physician-reviewed sleep apnea test performed in your own bed using a small take-home sensor kit, instead of an overnight stay in a lab.
Hypopnea
A partial reduction in airflow during sleep — less severe than a full apnea, but still significant enough to lower oxygen levels or trigger an arousal.
Humidifier
A heated water chamber attached to a CPAP or BiPAP machine that adds moisture to the airflow, reducing dryness and irritation.
Glossary terms starting with I
In-Lab Sleep Study
A polysomnography test performed overnight at a sleep clinic under technician supervision, typically reserved for complex or ambiguous cases.
Insomnia
Persistent difficulty falling or staying asleep, which may be investigated alongside — or instead of — a sleep apnea test depending on your symptoms.
Glossary terms starting with L
Level 3 Home Sleep Test
The clinical classification for a simplified home sleep apnea test that records airflow, effort, oxygen, and heart rate, but not brain waves.
Glossary terms starting with M
MSLT (Multiple Sleep Latency Test)
A series of scheduled daytime nap opportunities, performed the day after an overnight sleep study, used to help diagnose narcolepsy.
Mask Fit
How well a CPAP or BiPAP mask seals against your face — a poor fit is the most common reason people struggle with therapy.
Glossary terms starting with N
Narcolepsy
A neurological sleep disorder causing excessive daytime sleepiness and sudden sleep episodes, diagnosed through an overnight sleep study followed by an MSLT.
Nasal Cannula
A small tube with two prongs that rests at the nostrils to measure airflow — one of the core sensors used in a home sleep test.
Glossary terms starting with O
Obstructive Sleep Apnea (OSA)
The most common form of sleep apnea, caused by throat muscles relaxing and repeatedly blocking the airway during sleep.
Oximetry (Pulse Oximeter)
A fingertip sensor that continuously measures blood oxygen saturation (SpO2) and pulse rate throughout a sleep study.
Glossary terms starting with P
Polysomnography (PSG)
The comprehensive, multi-sensor recording of breathing, oxygen, heart rate, brain waves, and movement during sleep — the clinical gold-standard sleep study.
Parasomnia
Unusual behaviors during sleep, such as sleepwalking or acting out dreams, typically evaluated with a video-assisted sleep study.
PAP Therapy
The umbrella term for positive airway pressure treatments, including CPAP and BiPAP, prescribed after a sleep apnea diagnosis.
Physician-Reviewed Report
The clinical summary a qualified sleep physician prepares after scoring your sleep study, explaining your results and recommended next steps.
Glossary terms starting with R
REM Sleep
The sleep stage associated with vivid dreaming and rapid eye movement. Breathing muscles relax further in REM, so apnea events are often more frequent.
RERA (Respiratory Effort-Related Arousal)
A breathing event that doesn't fully qualify as an apnea or hypopnea but still triggers a brief arousal from sleep.
Glossary terms starting with S
Sleep Apnea
A disorder marked by repeated pauses or shallow breaths during sleep — the condition a sleep apnea test is designed to detect and grade.
Sleep Apnea Test
An overnight, sensor-based test — done at home or in a lab — that measures breathing, airflow, and oxygen levels to screen for sleep apnea.
Sleep Apnea Treatment
The therapy path recommended after a diagnosis, ranging from CPAP or BiPAP machine rental to oral appliances or lifestyle changes, based on severity.
Sleep Scan
A common everyday term for an overnight sleep study or sleep apnea test that records your breathing, oxygen, and other signals while you sleep.
Sleep Study
The general term for any overnight, sensor-based recording of sleep — from a basic home sleep test to full in-lab polysomnography.
Sleep Study Test
Another way of referring to a sleep study — the overnight, physician-reviewed test used to diagnose sleep apnea and other sleep disorders.
Somnia Scan
An alternate name sometimes used for a sleep study or sleep scan, referring to the overnight recording of breathing and sleep signals.
SpO2
The medical shorthand for blood oxygen saturation — one of the primary readings tracked throughout a sleep study.
Split-Night Study
A single overnight study that combines sleep apnea diagnosis in the first half of the night with CPAP titration in the second half.
Snoring
The sound caused by vibrating tissue in a narrowed airway. Frequent, loud snoring is one of the most common reasons people request a sleep apnea test.
Glossary terms starting with T
Titration Study
An overnight study, using CPAP or BiPAP, dedicated to finding the exact pressure setting that keeps a diagnosed patient's airway open.
Turnaround Time
The time between returning your home sleep test device and receiving your physician-reviewed report — typically a few days.
Glossary terms starting with U
UARS (Upper Airway Resistance Syndrome)
A milder form of airway narrowing that causes arousals and daytime sleepiness without meeting the full criteria for sleep apnea.
Glossary terms starting with V
Video Polysomnography (Video PSG)
A sleep study that adds synchronized infrared video to standard sensors, used to evaluate parasomnias like sleepwalking or REM behavior disorder.