AHI (Apnea-Hypopnea Index)
The number of apneas and hypopneas per hour of sleep. The most widely used measure of sleep apnea severity, but it misses flow limitation and RERAs.
What Is AHI (Apnea-Hypopnea Index)?
The Apnea-Hypopnea Index (AHI) counts the number of complete airflow cessations (apneas) and significant airflow reductions (hypopneas) per hour of sleep. It has been the primary metric in sleep medicine for decades, with severity categorised as: normal (fewer than 5 events per hour), mild (5 to 15), moderate (15 to 30), and severe (above 30).
However, AHI has significant limitations. It treats all events equally regardless of duration or oxygen impact. A 10-second apnea counts the same as a 60-second one. More importantly, AHI completely misses flow limitation and RERAs (Respiratory Effort-Related Arousals), which means a person can have an AHI under 5 while still experiencing significant sleep disruption from partial airway narrowing.
This is why many CPAP users with a "normal" AHI still feel exhausted. Their machine reports success, but the breathing restrictions that actually fragment their sleep go undetected by this single number. AirwayLab exists to fill this gap by analysing the flow waveform data that AHI ignores.
Normal Ranges
How AirwayLab Measures This
AirwayLab reads machine-reported AHI from the STR.edf file on your ResMed SD card. However, AirwayLab is specifically designed to go beyond AHI by computing flow limitation metrics (Glasgow Index, FL Score, NED) that detect the breathing problems AHI misses.
Try it with your dataFrequently Asked Questions
What is a normal AHI on CPAP therapy?
On CPAP therapy, an AHI below 5 events per hour is generally considered well-controlled. However, a normal AHI does not guarantee effective therapy. Flow limitation and RERAs can still fragment sleep without being counted in AHI.
Why am I still tired with a normal AHI?
AHI only counts complete or near-complete airflow reductions. Partial airway narrowing (flow limitation) and Respiratory Effort-Related Arousals (RERAs) can disrupt sleep without triggering an AHI event. Tools like AirwayLab analyse flow waveform data to detect these hidden breathing problems.
How is AHI different from RDI?
AHI counts only apneas and hypopneas. RDI (Respiratory Disturbance Index) also includes RERAs, making it a more comprehensive measure of breathing disruption. A person with an AHI of 3 might have an RDI of 15 if they have frequent RERAs.
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Medical Disclaimer
AirwayLab is not a medical device and is not FDA-cleared or CE-marked. It is provided for educational and informational purposes only. The analysis results should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult qualified healthcare providers regarding your sleep therapy and any changes to PAP settings.