Glossary
Plain-language definitions for every therapy metric and CPAP term CpapDash uses.
AHI
What it is
The Apnea-Hypopnea Index is the average number of breathing interruptions (apneas and hypopneas) per hour of therapy.
Range
On therapy, under 5 events per hour is generally considered well controlled. 5 to 15 is mild, 15 to 30 moderate, above 30 severe.
Why it matters
AHI is the headline measure of how well your therapy is keeping your airway open through the night. A low, steady AHI is the goal.
Blood oxygen (SpO2)
What it is
The percentage of oxygen your blood is carrying, measured by a pulse oximeter if you use one with the app.
Range
Typically 94 to 100 percent. Brief dips happen, but repeated drops below 88 percent are worth noting.
Why it matters
Untreated apneas can pull your oxygen down. Tracking SpO2 alongside AHI shows whether therapy is protecting your oxygen levels.
Central apnea
What it is
A pause in breathing where the brain briefly stops sending the signal to breathe, unlike an obstructive apnea where the airway is physically blocked.
Range
Occasional central events are normal. A rising count over time is what is usually flagged.
Why it matters
Central events are not fixed by increasing pressure the way obstructive events are, so a rising central count is worth raising with your provider rather than adjusting settings yourself.
Compliance
What it is
How consistently you use therapy, typically measured as the percentage of nights with at least 4 hours of use over a 30-day period.
Range
Most insurers require at least 70 percent of nights with 4+ hours to consider therapy "compliant."
Why it matters
Compliance thresholds were built around insurance requirements, not necessarily what is best for you. More hours per night generally means more protection, even above the minimum.
Desaturation
What it is
A temporary drop in blood oxygen level, usually caused by a pause or reduction in breathing.
Range
Brief, shallow dips are common. Repeated drops below 88 percent are worth discussing with your provider.
Why it matters
Desaturations are the direct downstream effect of untreated apneas. Tracking them shows whether therapy is protecting your oxygen, not just reducing event counts.
EPR (Expiratory Pressure Relief)
What it is
A comfort feature on ResMed machines that lowers the pressure slightly when you breathe out, then returns to the prescribed pressure on your next breath in.
Range
A comfort setting, not a measurement. Usually available at levels 1 to 3.
Why it matters
Lower pressure on exhale can make therapy feel less like breathing against resistance, which helps some people tolerate higher prescribed pressures.
Mask leak
What it is
Air escaping around the mask, reported here as the 95th percentile leak: the level your leak stayed under for 95 percent of the night.
Range
Under about 24 L/min is comfortable for most masks. Sustained higher leak usually means a fit or seal issue.
Why it matters
A big leak can drop the pressure actually delivered, blow air in your eyes, and fragment your sleep. Fixing leak often improves both comfort and AHI.
ODI (Oxygen Desaturation Index)
What it is
The average number of times per hour your blood oxygen drops by 3 percent or more from your baseline.
Range
Under 5 events per hour is generally considered normal. ODI often tracks closely with AHI.
Why it matters
ODI shows how often breathing events actually affect your oxygen levels, not just how often the events happen.
Obstructive apnea
What it is
A pause in breathing caused by the airway physically collapsing or blocking, even though your body keeps trying to breathe.
Range
This is the event type CPAP therapy is built to prevent. A well-fitted, well-pressured setup should keep these low.
Why it matters
Pressure holds the airway open against this kind of blockage, which is the core job CPAP therapy does.
Pressure
What it is
The air pressure the machine delivers, in cmH2O. We show the average and the 95th percentile across the night.
Range
Set by your provider, commonly between 4 and 20 cmH2O. Auto machines vary the pressure within a prescribed range.
Why it matters
Enough pressure keeps the airway from collapsing. Watching how it moves helps you and your provider fine tune the settings.
Respiratory rate
What it is
Your average breaths per minute during therapy.
Range
Roughly 12 to 20 breaths per minute at rest for most adults.
Why it matters
Unusual or shifting breathing rates can be a clue to central events or other changes worth mentioning to your provider.
Titration
What it is
The process of finding the right pressure, or pressure range, for your airway, either during a sleep study or automatically by an auto-adjusting machine.
Range
Set initially by a sleep study or your provider, then often fine-tuned automatically over time on an auto machine.
Why it matters
The prescribed pressure is a starting point, not necessarily final. Ongoing titration adjusts it as your needs change.
Usage hours
What it is
How long you wore therapy on a given night.
Range
Aim for your full sleep, 7 or more hours. 4 hours is the common minimum used for compliance, but more is better.
Why it matters
Therapy only helps while you are wearing it. The hours you are off the machine are hours your airway is unprotected.
This is general education, not medical advice. Talk to your provider about your therapy and before changing any settings.
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