How is the Apnea Hypopnea Index (AHI) determined during an at-home sleep test?

✓ Accepted answer

The Apnea Hypopnea Index (AHI) is determined by dividing the total number of apnea and hypopnea events recorded during an at-home sleep test by the total hours of sleep documented, yielding an events-per-hour rate.

• Event Classification: Sensors detect obstructive apneas, typically defined as airflow cessation lasting at least 10 seconds, and hypopneas, which are reductions in airflow of at least 30 percent accompanied by a desaturation of 3–4 percent or greater. Automated algorithms count these distinct events to establish the raw total for the night.
• Duration Calculation: The device calculates total sleep time by identifying periods where respiratory patterns indicate sleep, excluding wakefulness. The AHI divides the event count by this duration; for instance, 30 events over five hours of recorded sleep results in an AHI of 6.
• Severity Grading: Healthcare providers interpret the final number using standard benchmarks, where an AHI of 5 or less is normal, 5–14 indicates mild sleep apnea, 15–29 is moderate, and 30 or more is severe, which often necessitates CPAP therapy.
• Review Process: Following the overnight data collection, a licensed clinician reviews the raw files to verify event quality and adjust for potential measurement errors before finalizing the index and recommending treatment.

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