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The Apnea–Hypopnea Index or Apnoea–Hypopnoea Index (AHI) is an index used to indicate the severity of sleep apnea. It is represented by the number of apnea and hypopnea events per hour of sleep. Apnea is the complete absence of airflow through your nose and mouth. Hypopnea is a partial collapse of your airway, limiting breathing.
A Hypopnea Index (HI) can be calculated by dividing the number of hypopnea events during the sleep period by the number of hours of sleep. The Apnea-Hypopnea Index (AHI) is an index of severity that combines apneas and hypopneas. Combining them both gives an overall severity of sleep apnea including sleep disruptions and desaturations (a low ...
The respiratory disturbance index (RDI)—or respiratory distress Index—is a formula used in reporting polysomnography (sleep study) findings. Like the apnea-hypopnea index (AHI), it reports on respiratory distress events during sleep, but unlike the AHI, it also includes respiratory-effort related arousals (RERAs). [1]
The terms obstructive sleep apnea syndrome (OSAS) or obstructive sleep apnea–hypopnea syndrome (OSAHS) may be used to refer to OSA when it is associated with symptoms during the daytime (e.g. excessive daytime sleepiness, decreased cognitive function).
Obstructive sleep apnea or sleep apnea is defined as either cessation of breathing (apnea) for 10 seconds, or a decrease in normal breathing (hypopnea) with an associated desaturation in oxygen and arousal during sleep that lasts at least 10 seconds. In adults, it is typical to have up to 4.9 events per hour.
In the case of OSA, the outcome that determines disease severity and guides the treatment plan is the apnea-hypopnea index (AHI). [15] This measurement is calculated from totaling all pauses in breathing and periods of shallow breathing lasting greater than 10 seconds and dividing the sum by total hours of recorded sleep.
The most severe of the sleep apneas is obstructive sleep apnea. Apnea is obstructive only when polysomnography reveals a continued inspiratory effort, evidenced by abdominal and thoracic muscle contraction. Sleep apnea is measured by the apnea-hypopnea index (AHI). An AHI is determined with a sleep study.
UARS is diagnosed using the Respiratory Disturbance Index (RDI). A patient is considered to have UARS when they have an Apnea-Hypopnea Index (AHI) less than 5, but an RDI greater than or equal to 5. Unlike the Apnea-Hypopnea Index, the Respiratory Disturbance Index includes Respiratory Effort-related Arousals (RDI = AHI + RERA Index). [13]