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Apnea index (AI)

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The Apnea Index (AI) is the component of the Apnea Hypopnea Index (AHI) that represents the average number of apnea events that occur during each hour of sleep. Apnea events may be further classified as Obstructive sleep apnea (OSA) or Central sleep apnea (CSA), abbreviated OA and CA respectively.

Unlike the Apnea-Hypopnea Index, the apnea index only counts obstructive apnea (OA) and central apnea (CA) events and does not include hypopneas (H) as part of the equation. AI is derived from the sum of obstructive apnea and central apnea events divided by the number of hours of sleep.


           AI = (OA + CA) ÷ # of hours of sleep

If a person sleeps for 8 hours and experiences 5 OA and 5 CA, then the math will look like this:

           AI = (5 OA + 5 CA) ÷ 8 hours of sleep
                (10) ÷ 8
           AI = 1.25

The apnea index is a useful tool in the characterization of apnea type. By neglecting to consider hypopnea a more preferred approach to treatment can be ascertained as no individual will have exactly the same statistics for apnea events and apnea event types. By examining apnea index one may draw conclusions for the optimization of individual machine settings when other event types are compared.

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