Knowledge base
Support & learning library
42 articles and definitions, written for newly diagnosed users and veterans alike. Browse a category or search a term.
22 articles
20 glossary terms
6 categories
Getting started
If you were just diagnosed — start here.
Mask types
Pillow, nasal, full-face, hybrid — when each one wins.
Fit & comfort
Leaks, marks, headgear tension, side-sleeping.
Therapy basics
Pressure, ramp, humidification, EPR.
Buying & insurance
Prescriptions, retailers, replacement schedules.
Reviews & data
How summaries are generated and who submits them.
Glossary
Plain-English definitions of every CPAP term.
- AHI · Apnea-Hypopnea Index
- Average number of apnea or hypopnea events per hour of sleep. Below 5 is normal; 5–15 is mild OSA; 15–30 is moderate; above 30 is severe.
- APAP · Auto-titrating CPAP
- A machine that adjusts pressure breath-by-breath within a prescribed range, rather than holding one fixed pressure all night.
- BiPAP · Bi-level Positive Airway Pressure
- Delivers a higher pressure during inhale and a lower one during exhale. Often prescribed when standard CPAP feels hard to exhale against.
- Cushion
- The silicone or memory-foam piece that contacts your face and forms the seal. Wears out every 1–3 months.
- Deadspace
- The volume of air trapped between cushion and vent. Lower deadspace means CO₂ is flushed more efficiently with each breath.
- EPR · Expiratory Pressure Relief
- A ResMed comfort feature that drops pressure slightly when you exhale. Philips calls their version Flex.
- Frame
- The plastic skeleton that holds the cushion and connects to the headgear. Replaceable as a wear part.
- Full-face mask
- Covers both nose and mouth. Required for mouth breathers or those at high prescribed pressures.
- Headgear
- The fabric straps that hold the mask in place. Should be snug, not tight — over-tightening causes more leaks than it fixes.
- Hose · Tubing / circuit
- Connects the machine to the mask. Heated tubing prevents rainout in cold rooms.
- Hybrid mask
- A mask that seals under the nose (like a pillow) but also covers the mouth. Smaller profile than a true full-face.
- Leak rate
- Liters per minute of unintended airflow escaping the seal. Most machines report this nightly; under 24 L/min is generally fine.
- Mouth breather
- Someone whose mouth opens during sleep. Tends to need full-face masks, hybrid masks, or nasal masks paired with a chin strap.
- Nasal mask
- Covers the nose only, sealing on the bridge and upper lip. The middle ground between pillows and full-face.
- Nasal pillow
- Small silicone inserts that seal at the nostril opening rather than over the nose. Minimal facial contact.
- OSA · Obstructive Sleep Apnea
- The most common form of sleep apnea, caused by the throat tissue collapsing during sleep.
- Ramp
- A comfort feature that starts pressure low and builds to the prescribed level over 5–45 minutes, helping you fall asleep.
- Rainout
- Water condensing in the hose from the heated humidifier. Fixed with heated tubing or a hose cover.
- Titration
- The process of finding the right pressure for you — done in a sleep lab, or automatically by an APAP over the first few weeks.
- Vent
- The intentional holes in the mask that flush exhaled CO₂. Quieter on newer designs but never silent.